ORGANIC CHEMISTRY INTRODUCTION Organic chemistry = the chemistry of carbon compounds Carbon is not an abundant element in the universe is an essential element of life living organisms: carbon, hydrogen, nitrogen, oxygen trace elements: sulphur, phosphorous, sodium, potassium calcium, iron the unique properties of carbon permits the immense diversity of compounds associated with life. 1828, a German chemist Friedrich Whler : Organic chemistry object refers to: Isolation and purification of natural organic compounds, or those obtained in laboratories. Finding their structure, using different chemical and physical methods. Physico-chemical characterization of organic compounds. All organic compounds contain: without exception, carbon frequently hydrogen. can contain oxygen, nitrogen, halogens, sulfur, phosphorus, and rarely metals. organogenetic elements or organogens (C, H, O, N, S, P, Cl, F, Br, I, metals, etc) - the totality of chemical elements which form the composition of organic compounds hydrocarbons - compounds, formed only of carbon and hydrogen derivatives of hydrocarbons - substituting one or more hydrogen atoms with other type of atoms or groups of atoms K. Schorlemmer has defined organic chemistry as hydrocarbons chemistry and their derivatives. Classification of organic compounds Organic substances are classified according to the functional group they contain. A functional group is the atom or the group of atoms which confers specific physical and chemical properties to the molecules. According to the composition, the functional groups can be: homogenous: multiple bonds (double, triple) carbon carbon heterogeneous: contains or not carbon, and other types of atoms, -X, -OH, C=O, -COOH, etc Structure - the organizational pattern or arrangement of parts that characterizes a thing. Chemists - the manner in which the atoms that compose a molecule of a specific compound are attached (bonded) to one another and oriented in space. This information is usually provided by a structural formula Homogenous functional groups C CC CFunctional Group Formula Class Denomi nation Specific Example IUPAC Denomination Common Denomi nation Alkenes H2C=CH2 Ethene Ethylene Alkynes HCCH Ethyne Acetylene Arenes C6H6 Benzene Benzene Functional groups containing heteroatoms, bounded with simple bonds Functional Group Formula Class Denomi- nation Specific Example IUPAC Denomination Common Denomination halogenated derivatives H3C-I Iodomethane Methyl iodide Alcohols CH3CH2OH Ethanol Ethyl alcohol Ether CH3CH2OCH2CH3 Diethyl ether Ether Amines H3C-NH2 Aminomethane Methyl amine Nitro derivatives H3C-NO2 Nitromethane Thiol H3C-SH Methanethiol Methyl mercaptane Sulfides H3C-S-CH3 Dimethyl sulfide Functional groups with heteroatoms having multiple bonds Functional Group Formula Class Denomi-nation Specific Example IUPAC Denomination Common Denomination Nitrils H3C-CN Ethanenitril Acetonitril Aldehydes H3CCHO Ethanal Acetaldehyde ketones H3CCOCH3 Propanone Acetone Carboxylic acids H3CCOOH Ethanoic acid Acetic acid Esters H3CCO2CH2CH3 Ethyl Ethanoate Ethyl acetate Functional Group Formula Class Denomi-nation Specific Example IUPAC Denomination Common Denomination Acidic halides H3CCOCl Ethanoil chloride Acetyl chloride Amide H3CCON(CH3)2 N,N-Dimethyl-ethane-amide N,N-Dimethylacet-amide Acidic anhydrides (H3CCO)2O Ethanoic anhydride Acetic anhydride Important aspects of structural formulas: Composition: types and numbers of atoms that compose a molecule of a compound. Constitution: manner in which the component atoms of a molecule are bonded to each other. Different compounds having the same composition but different constitutions are called isomers. Configuration: shape of a molecule in three-dimensional space. Isomers differing only in configuration are called stereoisomers. Analytic steps to find the structure of a pure organic compound: Elementary analysis can be: Qualitative: finds the atoms forming the substance; Quantitative: finds the substance composition. Percent formula indicates the mass of each element from 100 grams of substance. It is determined using calculation and the elementary analysis data. If the percent sum is less than 100%, the difference represents the oxygen. Brute formula represents the smallest ratio of whole numbers (integer) between the component atoms of a substance. To find the number of component atoms in 100 grams of substance, the percent of each element is divided with its atomic mass, than the obtained numbers are divided to the smallest value, obtained during the previous operation. Example of brute formula: CH2. Molecular formula indicates the number and type of atoms forming the molecule, and is an integral multiple of brute formula. Example: (CH2)n. Structural formula indicates the atoms arrangement in the molecule; is determined using different physico-chemical methods. A specific molecular formula can represent many structural formulas (see isomerism). An appreciation of the organic compound nature can be done calculating the equivalent unstauration (EU). EU can be calculated for any compound, using the following formula: where: ni represents the atom number of type i (C, H, O, N, X, etc.) v represents the atom valence EU value of a real compound must be an integral, positive number, including zero. Each double bond or saturated cycle reduces with 2 the hydrogen atoms in a molecule, therefore the EU value will increase with one unit. Verifying the molecular formula can be done also by calculating the sum of all covalences of the chemical components in that compound. This number must be an even number. 2) 2 ( 2 += i i v nEUExample of calculation in elementary analysis Percentage formula: 64.6% C, 10.8% H and 24.6% O C: 64.4 g/ 12.001 g/mol = 5.38 atom-gram C : 1.54 = 3.49 H: 10.8 g/ 1.008 g/mol = 10.7 atom-gram H : 1.54 = 6.95 O: 24.6 g/ 16.00 g/mol = 1.54 atom-gram O : 1.54 = 1.00 brute formula : C3.49H6.95O1.00 Since the elements combine only in ratio of integral numbers, the brute formula must be multiplied by 2 Real brute formula : C7H14O2 molecular formula (C7H14O2)x. Molecular Weight = 130 x = 1 molecular formula: C7H14O2 The great number of carbon in compounds is possible because carbon has: the ability to form strong covalent bonds with other carbon atoms, also holds strongly the atoms of other nonmetals. Carbon atoms have the special property to form chains, rings, spheres, and tubes. Chains of carbon atoms can be thousands of atoms long, as in polyethylene Chemical bonds in organic chemistry high number of organic compounds > 9 millions carbon is present in all these compounds. carbon has unique properties, determined by the electronic structure: It has 4 electrons on the last layer, being in the middle of the second period, group 14 (IV< A) the most marked tendency in the period to form stabile octet configuration by sharing electrons - forms covalences. It can form 4 covalent bonds to each other (with itself) or to other organogenic elements. It is the only chemical element that forms, practically, an infinite number of covalent bonds to each other, generating carbon atom chains. It can form different chain arrangements, linear, branched, and cyclic. It can form: - sigma, simple covalent bonds; - double covalent bonds (containing a sigma and a pi bond); - triple covalent bonds (containing a sigma and two pi bonds). In some organic compounds, covalent-coordinative bonds can appear. These are formed by sharing of the two electrons in the bond, given only by one atom. CHHHNHHH Cl CHHHNHHH : + +Cl-Carbon atoms chains Chains are classified function of their structure, as: Saturated chains: linear, carbon atoms are bounded consecutively, in line: CH3-CH2-CH3 branched, carbon atoms are bounded as branches of the base chain (the longest one): CH3-CH-CH3 CH3 cyclic, carbon atoms are bounded by simple covalent bonds, forming a closed chain (a cycle): CH2-CH2 CH2-CH2 Unsaturated chains: linear, carbon atoms are bounded consecutively, in line: CH2=CH2-CH3, CHCH branched, carbon atoms are bounded also as branches of the base chain (the longest one): CH3-CH-CH=CH2 CH3 cyclic, carbon atoms are bounded by simple or double, covalent bonds, forming a closed chain (a cycle): CH2-CH2 CH=CH Aromatic chains: mononuclear polynuclear Types of carbon atoms When discussing structural formula, it is often useful to distinguish different groups of carbon atoms by their structural characteristics. A nular carbon (o) is one that is not bonded to any other carbon atom. H2C=O, H3C-NH2, HCOOH, etc. A primary carbon (10, p) is one that is bonded to no more than one other carbon atom, with a single, sigma, covalent bond. H3Cp-CpH3 A secondary carbon (20, s) is bonded to two other carbon atoms by sigma covalent bonds, or to one carbon atom with a double (sigma + pi) covalent bond. H3C-CsH2-CH3, H2Cs=CsH2 A tertiary carbon (30, t) is bonded to three other carbon atoms by sigma covalent bonds, or to one carbon atom with a double (sigma + pi) covalent bond and to another carbon atom with a single bond; or is bonded to a single carbon atom with a triple covalent bond (one sigma and two pi). H3C-CtH-CH3, HCtCtH, CH2=CtH-CH3 CH3 A quaternary carbon (40, q) is bonded to four other carbon atoms by sigma covalent bonds; or to other two carbon atoms with double bonds; or to three carbon atoms, with a double covalent bond and two single covalent bonds; or with a triple covalent to one carbon atom and with one single bond to another carbon atom. CH3 H3C-Cq-CH3, HCCq-CH3, CH2=Cq=CH2 CH3 Isomerism In most cases a molecular formula does not uniquely represent a single compound. Different compounds having the same molecular formula, but a different spatial arrangement are called isomers There are two main classes of isomers: constitutional isomers and stereoisomers. Constitutional isomers have the same number and type of atoms but which are sequentially connected differently. This isomerism type excludes any rearrangement that is due to the molecule rotation as a whole, or of a single peculiar bond. Example: molecular formula C2H6O ethanol CH3CH2OH dimethylether CH3OCH3 But the following a and b structures are not isomers, they represents one and the same substance - butane - with a practically infinite representation ways of free rotation around a single bond. C H3CH2CH2CH3C H3CH2CH2CH3a bStructural (constitutional) isomerism types 1. Chain (skeleton) isomerism - appears doe to the branching possibilities of carbon chains. There are 2 isomers of butane with the formula C4H10: butane and isobutane. Pentane C5H12 presents 3 chain isomers: n-pentane, 2-methyl-butane (isopentane) and 2,2-dimethyl-propane (neopentane). C H3CH2CH2CH3C H3CHCH3CH3C H3CH2CH2CH2CH2C H3C CH3CH3CH3C H3CH2CHCH3CH32. Position isomerism - the carbon skeleton of the compound remains unmodified, but the functional groups change their bond position to the carbon skeleton. For example, the molecular formula C3H7Br has 2 position isomers: 1-bromo-propane and 2-bromo-propane. Butanol, with the molecular formula C4H9OH, has 2 position isomers: 1-butanol and 2-butanol, but also 2 chain isomers, so that the total isomers number is 4. C H3CH2CH2Br C H3CHCH3BrC H3CH2CH2CH2OHC H3CHCH2CH3OHC H3CH2CHCH3OHC H3C CH3CH3OH Position isomers are found, also in the benzene case. For example, the molecular formula C7H8Cl presents 4 isomers of benzene nucleus: 3. Functional isomerism - is found to the compounds, which contain different functional groups, so they belong to different classes of compounds. For example, the molecular formula C3H6O corresponds to propanal (an aldehyde), propanone (a ketone) or 2- propenol (a monounsaturated alcohol of propene) CH2Cl CH3ClCH3ClCH3ClC H3CH2COHC H3COCH3C H2CHCH2OH4. Tautomerism - constitutional type of isomerism - a rapid and facile interconvertion of one form into the other -tautomerides isomers differ in the position of one hydrogen atom. cyclic form linear form at glucose - due to the possibility of the aldehyde group in the molecule to react with a hydroxyl group in the same molecule, forming a cycle. In solution, a chemical equilibrium is established between the tautomeric forms. The concentration ration at equilibrium depends of factors as temperature, solvent nature, pH, etc. The tautomeric reaction is catalyzed by bases (by deprotonation reactions with delocalized anions formation), or acids (by protonation reactions or delocalized cation formation). Keto-enol tautomerism (a compound that contains a ketone group C=O is in equilibrium with the enol form that has a hydroxyl group attached to a carbon atom implied in a double bond C=C) Keto-enol tautomerism is important in biochemistry to explain the high transfer capacity of the phosphate group of phosphoelolpyruvate, the enol, instable form, which passes by dephosphorylation in the keto, stable form. COCHC COHketone enol C H3COCOOH C H2COHCOOHpyruvic acid enolpyruvic acid Amide-imide tautomerism amide imide acetamide acetimide Lactam-lactim tautomerism appears in heterocycles, ie in the nitrogen bases guanine, thymine and cytosine CONHC NOHC H3CONH2C H3COHNHNHNNH2ONNNH2OHCytosine - lactam form cytosine - lactim form 5. Stereoisomerism type Carbon atoms are secventionally connected in the same way but their spatial arrangement differs. Stereoisomers are divided in: conformational isomers, which are interconvert by the rotation around a single bond, and configurational isomers to which the simple interconvertion is not possible Configurational isomerism contains enantiomers and diastereoisomers HCH3CH3Hconformational isomersHCH3CH2CH3BrHCH3BrCH3CH2configurational izomers asymmetric carbon : a carbon atom that is bonded to four different atoms or groups and which loses all symmetry chiral configuration This type of configurational stereoisomerism is termed enantiomorphism, and the non-identical, mirror-image pair of stereoisomers that result are called enantiomers pairs of enantiomers their physical and chemical properties are largely identical HCH3CH3CH2BrHBrCH2CH3C H3** chiral compound perturb plane-polarized light in opposite ways. This perturbation is unique to chiral molecules, and has been termed optical activity. The instrument called a polarimeter, shown in the diagram below, can determine the plane of polarization One enantiomer will rotate polarized light in a clockwise direction, termed dextrorotatory or (+), and its mirror-image partner in a counter-clockwise manner, termed levorotatory or (). Specific Rotation where l = cell length in dm, c = concentration in g/ml D is the 589 nm light from a sodium lamp Compounds that rotate the plane of polarized light are termed optically active. A 50:50 mixture of enantiomers has no observable optical activity. Such mixtures are called racemates or racemic mixtures, and are designated (). 1. resolution separation of racemate into its component enantiomers. 2. racemization transformation of a pure enantiomer into its racemate. The existence of a symmetry plan cancels the optical isomerism, for example the presence of two identical substituents bonded to the same carbon atom. mezo - form Configurational stereoisomers which are not found in an enantiomeric relationship (optical isomers) are called diastereoisomers Diastereoisomers which are not chiral and do not contain stereogenic centers are called geometric isomers (cys/trans). These isomers appear doe to a restriction of the free rotation around of a bond. CCH3O H BrC O H BrCH3 Free rotation alt the level of a single bond The presence of a double bond block the free rotation around that bond, and two position isomers appear: one cys (the identical substituents are on the same part of the double bond) and trans (identical substituents are on one side and the other side of the double bond). C CO HO HBrBrOHOHC CO HO HBrOHBrOHC CClBrBrClC CClBrClBrtranscisIzomers Constitutional Izomers Stereoizomers Conformational Izomers Configurational Izomers Diastereoizomers Enatiomers cis-trans Izomers Diastereoizomers with stereogenic center Reaction mechanisms in organic chemistry Reaction mechanism - pathway followed by a chemical process with the intermediary chemical species (which cannot be isolated) that appear during the transformation of reactants into products. Classification: Electrophilic addition Electrophilic substitution Nucleophilic addition Nucleophilic substitution Radicalic substitution Radicalic addition Elimination Electrophilic addition Electrophile - the chemical specie that presents affinity for negative charges (molecular regions with electron excess). Electrophile species realize chemical bonds by accepting a pair of electrons. Examples: H+, CH3+, Cl+ etc. Alkenes give electrophilic addition with halogens, halogen hydride, water, etc. Example: the addition of hydrobromic acid to ethene, which has the following steps: 1st Step. Braking of the H-Br bond ions H+ and Br-: 2nd Step. The ion H+ (an electrophile) is attracted by the t electronic cloud of the double bond in the ethene accepts a pair of electrons. 3rd Step. The hydrogen ion binds to ethene and a carbocation results: 4th Step. The already formed carbocation has the tendency to attract the bromide ion, formed in the first step; finally the addition product results: bromoethane. CH2= CH2 + H-Br CH3- CH2- Br Electrophilic substitution Substitution reaction presumes the replacing of an atom or a group of atoms in a molecule with another atom or group. The electrophilic substitution reactions are characteristic to the systems that contain benzene nuclei. Examples of that type of substitution are halogenation, alkylation, acylation, nitration, sulfonation of benzene. Example: the nitration mechanism of benzene 1st Step. The reaction between sulfuric acid and nitric acid, at 50C, forms the electrophilic ion NO2+: H2SO4 + HNO3 HSO4- + NO2+ + H2O 2nd Step. Two of the delocalized electrons of benzene are attracted to the electrophilic specie, forming a bond. The resulting specie has a complete positive charge and a delocalization of the t electrons. 3rd Step. The resulted system formed in step 3 has the tendency to accept a pair of electrons from the negative ion, resulted during step 1. Nitrobenzene is formed: Nucleophilic addition It is an addition reaction, characteristic to aldehydes and ketones; it presumes an initial attack of a nucleophilic specie. A nucleophilic specie - negative charged ion, which has affinity for a molecular region with electron deficit (positive charge). Examples: HO-, CN- etc. Example: acetaldehyde reaction with hydrocyanic acid is a typical example of nucleophilic addition: 1st Step. Heterolytic braking of the bond H-CN to form the nucleophile CN-: HCN H+ + CN- 2nd Step. Cyanide ion attacks the carbon atom of the aldehyde group, which is positive due to the vicinity of the electronegative oxygen atom. The double bond C=O is transformed in a single one by the movement of the electron pair to the oxygen atom. 3rd Step. The chemical specie, formed as a result of the nucleophilic attack and rearrangement of electrons that form the double bond, is an anion: 4th Step. The negatively charged oxygen atom attracts the hydrogen positive ion, which forms a bond with the oxygen, by accepting the pair of electrons. 5th. Step. Finally, a new molecule results that has two functional groups: nitrile and hydroxyl. Nucleophilic substitution Nucleophilic substitution mechanism: Halogen derivatives of alkanes hydrolyze in an alkaline medium (sodium hydroxide solution) to form an alcohol. Example is the hydrolysis of ethyl chloride. 1st Step. The hydroxyl ion attacks the carbon atom situated in the closed vicinity of chlorine. (Carbon atom has a partially positive charge due to the electron attracting effect of chlorine atom 2nd Step. An intermediary, with double function, is formed: 3rd Step. The bond C-Cl is broken and ethanol is formed. + Cl- Cl- + Na+ NaCl Radicalic substitution implies the attack of free radicals, formed in a hemolytic braking. A simple example is the alkanes reaction with halogens in the presence of UV radiation. Example: radicalic chlorination of methane 1st Step. The initiating step the Cl-Cl bond is broken due to the UV radiation to form two chlorine free radicals: Cl + Cl 2nd Step. Propagation step a free radical reacts with a molecule to form a new radical and a new molecule. 3rd Step. Termination step Two free radicals react to form a molecule. Radicalic addition It is an addition reaction that implies radicalic species. For example: polymerization of ethene (ethylene) to form polyethylene: nCH2=CH2 [-CH2-CH2-]n The reaction takes place at 200C and 2000 atm, in the presence of small quantities of initiators, capable to form free radicals in the given conditions. 1st Step. Initiating step free radical species (RCH2-CH2) are formed in the reaction between an ethene molecule and the free radical R, formed from the initiator. 2nd Step. Propagation step corresponds to the following reaction: RCH2-CH2 + CH2=CH2 RCH2-CH2-CH2-CH2 3rd Step. Termination step - Two radical species react to form a non-radicalic compound. For example: RCH2-CH2-CH2-CH2 + CH2-CH2-CH2-CH2R RCH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2R HYDROCARBONS combinations of carbon with hydrogen. all organic compounds can deriver from hydrocarbons by replacing of hydrogen atoms with other elements or groups of atoms. Besides, carbon monoxide and carbon dioxide are inorganic substances, even if they can be considered as derivatives of methane. Carbon has the almost unique property to combine with itself, forming linear, branched and cyclic chains. Hydrocarbons formulas are obtained by saturation the rest of the valences with hydrogen atoms. Example: CH4 CH3 CH3 CH3 CH2 CH3 Methane Ethane Propane The hydrocarbons with > 3 carbon atoms structural (chain) isomers - linear (straight) - branched chains; The higher the number of carbon in the molecule the higher is the number of chain isomers that are possible to exist. The maximum number of hydrogen atoms that can be bonded to n carbon atoms is 2n + 2. saturated hydrocarbons have the general formula CnH2n+2 Alkanes all carbon atoms are sp3 hybridized Cycloalkanes that have the chain closed in a ring or circle CnH2n. unsaturated hydrocarbons - carbons bound by double bonds and they have a hybridization sp2 alkenes triple bonds hybridization sp alkynes aromatic hydrocarbons - benzene. homologue series - the series of organic compounds that have the same general formula and form of the chain, and the consecutive terms differ by a methylene group (-CH2-) Two consecutive compounds in a homologue series are called homologue terms. Saturated non-cyclic hydrocarbons alkanes general formula CnH2n+2. contain only simple, sigma bonds (C-C C-H) are also called paraffines (from Latin: parum affinis = low affinity). natural gases contain hydrocarbons with C1 C4 atoms and crude oil (petroleum) contains a mixture of liquid hydrocarbons (alkanes, cycloalkanes and aromatic compounds) and other organic compounds with sulfur, nitrogen, oxygen. Petrol (gasoline) is a mixture of alkanes and isoalkanes, especially with 8 carbon atoms. Nomenclature The first four terms of the homologue series of alkanes have specific names: methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10). superior terms suffix ane is added to the Greek name of the number of carbon atoms in the molecule (see next table). normal alkanes have straight chain isoalkanes have branched chain No of C atoms Denomination Molecular formula Structural formula 1 Methane CH4 CH4 2 Ethane C2H6 CH3CH3 3 Propane C3H8 CH3CH2CH3 4 Butane C4H10 CH3CH2CH2CH3 5 Pentane C5H12 CH3CH2CH2CH2CH3 6 Hexane C6H14 CH3(CH2)4CH3 7 Heptane C7H16 CH3(CH2)5CH3 8 Octane C8H18 CH3(CH2)6CH3 9 Nonane C9H20 CH3(CH2)7CH3 10 Decane C10H22 CH3(CH2)8CH3 12 Dodecane C12H26 CH3(CH2)10CH3 20 Eicosane C20H42 CH3(CH2)18CH3 A radical is obtained by the removing of one or more hydrogen atoms from the alkane molecule. The radical has an unpaired electron at the carbon atom that has lost the hydrogen. The symbol of the radical is obtained by adding a dot (CH3), but usually the valence line is used (CH3). The name of the radical depends on the number of lost hydrogen atoms from one - or two -carbon atoms. The monovalence radicals: suffix ane yl (alkyl). The divalence radicals: suffix ane ene if the two hydrogen atoms are removed from two different carbon atoms; suffix ane yliden when the two hydrogen atoms are removed from the same carbon atom The trivalence radicals: ane ine. CH3 CH3CH2 CH2 CH2CH2 CH methyl ethyl methyliden ethandiyl methylydine (methylene) (ethylene) (methine) The denomination of the isoalkane is done indicating the position of the substituents and the name of the respective radical, in the alphabetic order. Physical properties the bonds C-C and C-H are non-polar molecules are hydrophobic. Only weak attraction forces, van der Waals, manifest between molecules. Function of their molecular masses, and due to the weak attraction forces: the inferior alkanes (C1-C4) are gaseous, the alkanes having 5 to 17 carbon atoms are liquids, and the ones having more than 18 carbon atoms are solid at room temperature. The melting and boiling points increase in the homologue series with the increase in the number of carbon atoms in the molecule, and are greater at the normal (straight) alkanes than the isoalkanes with the same number of carbons 6 5 4 3 2 1 1 2 3 4 5 6 7 CH3-CH-CH2-CH-CH-CH3 CH3-CH-CH2-CH-CH2-CH-CH3 I I I I I I CH2CH3 CH3CH3 CH3 CH3 C2H5 2,3,5-trimethylhexane 6-ethyl-2,4-dimethylheptane Example: The boiling point of: pentane CH3-CH2-CH2-CH2-CH3 -b.p. 36.1C neopentane - b.p. 9.4C CH3 I CH3 C CH3 I CH3 Alkanes can be dissolved in: hydrocarbons from other classes and in halogenated compounds, but are insoluble in water and in the inferior alcohols. The alkanes density is lower, comparing with water (they float on water). Chemical properties low chemical reactivity, especially toward the ionic reagents (bases, weak mineral acids) due to the absence of the functional groups in their molecules. The chemical reactions of alkanes are: Substitution reactions: dehydrogenation or oxidation: CH bonds are broken. Isomerisation reactions, thermal decomposition CC bonds are broken burning Different derivatives can be obtained from alkanes, as alkenes, alkynes, alcohols, aldehydes, halogenated derivatives, hydrogen cyanide, etc. Isomerisation reactions - alkanes isoalkanes. Example: normal hexane 3-methylpentane. Oxidation reactions - function of conditions alcohols, aldehydes (ketones) or carboxylic acids. a. Methane oxidation to methanol; p = 130 200 atm and t = 300-400C. b. Methane oxidation to formaldehyde; t = 600C and catalysts nitrogen oxides. CH3 - (CH2)4 - CH3 50-100AlCl3, AlBr3oCCH3 - CH2 - CH - CH2 -CH3 ICH3methanol OH CH O 1/2 CH3C 400 - 300 atm, 200 - 1302 4 + de formaldehy O H O CH O CH2 2C 600 - 400 NO, 2 4 + + c. Isoalkanes oxidation is easier than the alkanes one. Isobutane is oxidized even with potassium permanganate (oxidation of the tertiary carbon). d. Alkanes combustion (burning) can be done with oxygen or air, at high temperature. Carbon dioxide and water result. The reaction is highly exothermic. CH3CCH3HCH3+ [O] KMnO4CH3CH3CH3OHCisobuthanolQ O 2H CO 2O CH2 2 2 4 + + +Thermal decomposition of alkanes t > 300C; C-C and C-H bonds are broken. - cracking - when CC bonds are broken an alkane and an alkene - dehydrogenation - braking of the CH bonds alkenes Substitution reactions replacement of one or more hydrogen atoms with atoms or groups from the reactant. - halogenation - hydrogen replacement with a halogen atom (Cl, Br), - Alkane chlorination takes place in the light (radiation) presence or at high temperatures (t > 500C). CH4 + Cl2 CH3Cl + HCl Chloromethane Chlorinated derivatives, used in medicine as anesthetics, are trichloromethane (chloroform CHCl3) ethyl chloride (CH3CH2Cl). ethene ethane CH CH CH - CH CH - CH - CH - CH2 2 3 3 3 2 2 3 = + butene CH - CH CH - CH CH - CH - CH - CH3 3 3 2 2 3 2H + = Alkenes Definition. Nomenclature Alkenes = olefins - are acyclic hydrocarbons that contain simple bonds CC and CH and only one double bond between two carbon atoms. general formula - CnH2n. The double bond (unsaturation) determines the chemical properties. It is formed of an type bond (very stable) and a type bond, with a much lower stability. Alkenes denomination - suffix ane in the alkane name ene (ethane ethene, propane propene, butane butene, etc.) An older denomination replaces suffix ene with ylene (ethene ethylene, propene propylene). In the case of a branched chain, the denomination follows the same rules as for alkanes. The longest chain chosen for the root name must include both carbon atoms of the double bond. If more than one double bond is present the compound is named as a diene, triene or equivalent prefix indicating the number of double bonds and each double bond is assigned a locator number. CH2 = CH2 CH2 = CH CH3 H2C = CH CH2 CH3 H3C CH = CH CH3 ethene propene 1-butene 2-butene Physical properties similar physical properties as alkanes. lower boiling points than the corresponding alkanes and higher densities. First terms of the alkenes series are gaseous, the middle terms are liquids and the superior ones are solids. water insoluble, but soluble in organic solvents. Chemical properties addition, oxidation, polymerization and substitution at the carbon atom in the allyl position Alkenes have a chemical reactivity higher than the alkanes. The alkenes characteristic reactions are: Addition to the double bond C C Substitution of hydrogen atoms in the allyl position. C CCH2additionsubstitutionAddition reactions the bond is broken aturated compound are synthesized. a. Halogen addition to alkenes forms dihalogenated saturated compounds. It is an easy reaction for chlorine and bromine, in a gaseous or liquid medium. For iodine, the reaction takes place only in the presence of light. CH3 CH2 CH CH2 + Cl2 CH2 CH CH2 CH3 1-butene I I Cl Cl 1,2-dichlorbutane b. Hydrogen addition gives alkanes. c. Hydracids addition forms monohalogenated derivatives (monohalogeno alkanes): CH2 = CH2 + HCl CH3 CH2Cl Ethene ethyl chloride Addition takes place differently: unoriented for symmetric alkenes and oriented for the asymmetric ones: The Markovnikov : during the hydracids addition to the asymmetric alkenes, the halogen atom binds to the hydrogen poorer carbon atom implied in the double bond propane propene CH - CH - CH H CH CH - CH3 2 3atm 200 C, 200 - 80 divizate, fin Pd Pt, Ni,2 2 3 + = d. Water addition to alkenes forms alcohols. The real reactant is hydronium ion H3O+, formed during the reaction between the acidic catalyst and water: CH3 CH = CH2 + H OSO3H CH3 CH CH3 , O SO3H isopropyl sulfate CH3 CH CH3 + H OH CH3 CH CH3 + H2SO4 , , O SO3H OH isopropylic alcohol Oxidation reaction to alkenes can be different, according to the oxidant. a. mild oxidation (oxidizing agent is potassium permanganate, in a weak basic medium), the double bond is broken. A diol results: b. strong oxidation (example with potassium permanganate in sulfuric acid medium), acids or ketones are formed, function of the alkenes structure. The reaction can be used to find the double bond position in the carbon chain. ol etylenglyc (glycol) ethandiol ethene(OH) CH - (OH) CH O H [O] CH CH2 2CO Na , KMnO2 2 23 2 4 + + =CH3CH3C CH CH3 3[O] CH3CH3COCH3COOH + +2-methyl-2-buteneacetone acetic acid CH3CHCH CH3+ 4[O] 2 CH3COOH2-butene acetic acid CH3CH3CH3CH3C+ 2[O]CH3CH3CO 2 C2,3-dimethylbutene acetone Polymerization reaction represents the chemical process in which a high number of unsaturated compound are bond to each other, forming a macromolecule. - The initial compound is denominated monomer, and the final product, polymer. - Monomers can be alkenes or their derivatives, generally denominated vinyl monomers. - Polymers are solid substances, with plastic properties (plastomers) or elastic (elastomers). n CH2 = CH ( CH2 CH )n I I CH3 CH3 polypropylene Alkynes - acyclic hydrocarbons that contain a triple bond between 2 C - General formula is: CnH2n-2. - contain in their molecule carbon atoms in two hybridization states: sp (carbon atoms of the triple bond one bond is and the other two are ) and sp3 (the rest of them). No. of C Denomination Molecular Formula Structural Formula 2 Acetylene (ethyne) C2H2 HC CH 3 Propyne (methylacetylene) C3H4 CH3 C CH 4 1-butyne (ethylacetylene) C4H6 CH3 CH2 C CH 5 1-pentyne C5H8 CH3 CH2 CH2 C CH 6 1-hexyne C6H10 CH3 CH2 CH2 CH2 C CH Denomination : suffix ane yne (ethane ethyne, propane propyne, butane butyne, etc.) The most important alkyne is acetylene. Physical Properties aggregation state depends on the carbon atom number, the first three terms of this homologous series being gaseous. water solubility is much higher than the alkanes and alkenes, due to the polarization of the bond CH. Alkynes solubility increases a lot with pressure. Chemical Properties unsaturated hydrocarbons, containing a triple bond stronger unsaturated character than that given by the double bond. Acetylene participates to: addition reactions, dimerisation (to form vinylacetylene), trimerisation (forming aromatic compounds), oxidation (to form acids oxalic acid) and substitution. Addition reaction a. Hydrogen addition alkanes or alkynes. Pb poisoned Pt HC CH + H2 -----------------------> CH2 = CH2 acetylene ethene Ni HC CH + 2 H2 -----------------------> CH3 CH3 acetylene ethane b. Halogens addition. Bromine and chlorine give an easy addition to acetylene. methane tetrabromo - 1,1,2,2 hene dibromomet - 2 1, acetyleneCHBr - HC Br CHBr BrHC Br CH HC2 2Br22 = + +c. Acids addition (inorganic or organic) to acetylene is easily realized lower unsaturation grade (triple bond becomes double bond, the type being vinyl monomers. - Hydrochloric acid addition: - Acetic acid addition: - Hydrogen cyanide addition chloride vinyl CHCl CH HCl CH CH2170 , HgCl2= + Cacetate vinyl CH - CO - O - CH CH COOH - CH CH CH3 2C 200 , COO) Zn(CH32 3= + il acrylonitr CHCN CH HCN CH CH280 Cl, NH Cl Cu4 2 2= + + C d. Water addition to acetylene (Kucerov reaction) acetaldehyde Vinyl alcohol (instable intermediary compound) tautomerizes to form acetaldehyde. Substitution reactions Hydrogen atoms, bounded to a carbon atom that belongs to a triple bond, has a weak acidic character. acetylene is more acidic than ethene or ethane. The hydrogen atom can be easily given to a strong base. A class of substances is formed, denominated acetylides. de acetaldehy alcohol vinyl O CH - CH OH] - CH [CH O H CH HC3 2 2 = = + acetylide disodium H Na C C Na 2Na CH HCacetylide monosodium H 1/2 Na C HC Na CH HC2- - C 2002- C 150+ + + + + ++Dimerization reaction. One acetylene molecule is added to another one and an enyne compound is formed (vinylacetylene). HCl can be added to vinylacetylene to form chloroprene (monomer in the synthetic rubber synthesis) CH2=CH-CCH + HCl CH2=CH-C=CH2 Cl Trimerisation reaction. Acetylene trimerisation forms a benzene ring. The reaction can take place thermically or catalytically (with complexes of transition metal as catalyzers). acetylene vinyl CH C - CH C H CH HC CH HC2C 100 - 80 Cl, NH , CuCl4 2 = + CHHC600-800oCbenzene3Aromatic hydrocarbons (arene) Definition. Classification aromatic hydrocarbons or arene - hydrocarbons, which have as basic structurally unit the benzene ring, ArH. Aromatic hydrocarbon radicals are denominated aryl radicals Ar-. The characteristic compound of this series is benzene C6H6. Classification (following the benzene ring numbers in the molecule): Mononucleus, example: benzene, toluene, xylene: CH3CH3CH3benzentoluene xylenee - Polynucleus - with isolated nucleus (difenyl) - with condensed nucleus (naphthalene, anthracene, phenanthrene) Physical properties The aggregation state of aromatic hydrocarbons is liquid for the mononucleus ones and solid for the polynucleus ones. water insoluble but soluble in different organic solvents. Their density is lower than waters but higher than the other hydrocarbons. Benzene and toluene are used as solvents. Naphthalene sublimates. DifenylNaphthaleneAnthracenePhenanthreneChemical properties Aromatic hydrocarbons give substitution reactions, additions and oxidations to the nucleus or to the side chains. Even benzene looks like an unsaturated compound, the electrons form a common cloud which belongs equally to the 6 carbon atoms, which become equivalents as chemical reactivity. benzene gives easier substitution reactions than addition ones, having an aromatic character. Reactions of the aromatic nucleus a. Substitution reactions, characteristic to benzene a. Friedel-Crafts alkylation b. Friedel-Crafts acylation + CH3CH2ClAlCl3 + HClCH2CH3ethylbenzeneethyl chloride+ CH3 - CO - ClAlCl3C OCH3acetyl chloridefenyl-methyl-ketone+ HCl+ HONO2H2SO4+ H2ONO2nitric acid nitrobenzene+ Cl2FeCl3Cl+ HClmonochlorbenzene+ HOSO3HSO3H+ H2Obenzene-sulphonic acidc. Nitration reaction d. Halogenationreaction e. Sulfonation reaction - Substituent orientation on the benzene nucleus. The first substituent of benzene nucleus enters randomly in any position of the benzene ring. If a benzene ring has already a substituent, the substitution reaction is oriented, the position of the second substituent being determined by the preexisting substituent, which can be: First order substituent orients the new substituent on the positions ortho (2) and para (4): halogens, -OH, -NH2, -CH3, -C2H5, -N(CH3)2 Second order substituent -NO2, -COOH, -CHO, -SO3H, -CN, which orients the new substituent in the meta (3) position: 2 + 2 H2O+ 2HONO2CH3CH3CH3NO2NO2toluene o-nitrotoluene p-nitrotoluene+NO2+Cl2AlCl3NO2Cl+ HClnitrobenzene m-chloro-nitrobenzene Naphthalene substitution takes place similarly to the benzene one. First substituent will prefer the more reactive position. + HONO2H2SO4-H2O+HONO2-H2Onitrobenzene m-dinitro-benzene 1,3,5-trinitrobenzeneNO2NO2NO2NO2NO2O2No o o o ||||+ HONO2 H2SO4NO2+ H2Oo nitronaphthaleneb. Addition reactions. Benzene can add: hydrogen (at 250C in the platinum presence, forming cyclohexane), chlorine (at light, forming hexachlorcyclohexane). Polynucleus arenes give easier addition reactions. Hydrogen addition Chlorine addition C H2C H2CH2CH2CH2CH2+ 3H2 cyclohexanet + 3Cl2ClHHClHClHClHClHClhexachlorcyclohexanehvc. Oxidation reactions. The aromatic ring is relatively stable to oxidation Benzene can be oxidized with air in the presence of vanadium pentoxide, at 450C, forming maleic anhydride. Naphthalene (with an aromatic character weaker than benzenes) is oxidized in milder conditions (at 360C, with air and vanadium pentoxide), forming phthalic anhydride. HC - COOHHC - COOH9/2 O2-2CO2 -H2O-H2OHCHCCOOOCmaleic acid maleic anhydride+ 9/2 O2Vn2O5, 360oC-2CO2-H2OCOOHCOOH-H2OCCOOOphthalic anhydride phthalic acid Anthracene is oxidized with oxidizing agents or air ant catalysts, only the middle air being affected. Side chain reactions. The saturated alkyl side chain gives saturated hydrocarbon characteristic reactions. Hydrogen atoms, found at the carbon atom bounded directly to the benzene ring (benzyl position) are more reactive than the chain. Halogenation (Cl2, Br2) in the light presence or at high temperature. + 3 [O]CC+ H2OOOanthraquinone+ Cl2+ HClCH3CH2 - Clbenzyl chloride Oxidation (in strong conditions, with oxidizing agents like potassium permanganate or potassium dichromate at warm). CH3COOHtolueneacid benzoic3[O]benzoic acidFUNCTIONAL DERIVATIVES Halogenated compounds Definition. Nomenclature contain in molecule one or more halogen atoms as functional group. are derivatives of hydrocarbons by replacing hydrogen atoms with halogen atoms. (F, Cl, Br, I). According to the halogen atom number, they are mono- and polyhalogenated. Denomination - adding the halogen name as prefix to the hydrocarbon name : - halide of the hydrocarbon residue: CH3Cl monochloro-methane, methyl-chloride CH2=CH-Cl monochloro-ethene, vinyl-chloride CH3-CH2-CH2-Cl 1-chloropropane, propyl-chloride CH3 CH CH3 2-chloropropane (isopropyl chloride) | Cl If two halogen atoms are found at the same carbon atom, they are called geminals, those found in the positions 1, 2 are called vicinals. Br | CH3 C CH3 Br CH2 CH2 Br | Br 2,2-dibromopropane 1,2-dibromoethane geminal vicinal Physical Properties The saturated halogenated compounds, having a low carbon number, are gaseous at room temperature, the other are liquid or solid. are water insoluble, but soluble in majority of organic solvents. Their density is higher than water density. Chemical Properties According to the substitution reaction: normal reactive compounds (derivatives of alkanes), increase reactivity compounds (with an alyl or benzyl halogen) and low reactivity compounds (halogen bounded to a vinyl or aromatic carbon). Substitution Reaction Hydrolysis Reaction forms, function of the halogenated derivative type, different classes of compounds: alcohols, in the monohalogenated comp. carbonyl compounds, in the case of geminal dihalogenated comp. organic acids, in the case of geminal trihalogenated comp. ethanol e chlorethan NaCl OH - CH - CH Cl - CH - CH2 3HOH NaOH,2 3 + + aldehyde benzoic chloride benzyliden2NaCl O CH - H C CHCl - H C5 6HOH 2NaOH,2 5 6 + = +ion acetate thane trichloroe3NaCl COO - CH CCl - CH-3HOH NaOH, 3 3 3 + + Reaction with alkaline cyanides (sodium or potassium) nitriles, permitting to form a new carbon-carbon bond (reaction to increase the chain) Reaction with magnesium takes place in anhydrous ether medium organomagnesium compounds (Grignard reagents). Reaction with ammonia aliphatic halogenated compounds react with ammonia at high pressure to form amines. le acetonitri NaI CN - CH NaCN I CH3 3 + +bromide magnesium fenyl MgBr - H C Mg Br - H C5 6 5 6 +e methylamin Cl NH NH - CH 2NH Cl - CH4 2 3 3 3 + + Friedel-Crafts Reaction it is based on the aliphatic halogenated compounds property to react with arenes in the presence of anhydrous aluminum chloride. Hydracids elimination reaction Halogenated derivatives are treated with strong bases in alcoholic medium alkenes are formed. toluen HCl CH - H C Cl CH H C3 5 6AlCl3 6 63+ +ethene HCl CH CH Cl - CH - CH2 2alcoolic KOH2 3 + = Hydroxylic compounds Alcohols Definition have the functional group hydroxyl (-OH). can be considered as water derivatives in which one hydrogen atom has been replaced with an organic radical (R OH). Nomenclature Prefix hydroxy or suffix ol is added to the basic hydrocarbon denomination (hydrocarbon radical name + alcohol) CH3 OH methanol, methyl alcohol, hydroxymethane CH3 CH2 OH ethanol, ethyl alcohol, hydroxyethane Classification - following three criteria: the nature of the organic radical to which the OH is bounded: saturated alcohols (alcohols): CH3 CH2 OH (ethyl alcohol) unsaturated alcohols (enols): CH2 = CH OH (vinyl alcohol) aromatic alcohols: C6H5 CH2 OH (benzyl alcohol) the number of the functional groups: monohydric alcohols: CH3 CH2 OH (ethyl alcohol) di (poly)hydric alcohols: CH2 CH2 I I OH OH 1,2-ethanediol (glycol) CH2 CH2 CH I I I OH OH OH glycerol carbon atom nature to which the functional group is bounded: primary alcohols: CH3 OH secondary alcohols: - isopropyl alcohol tertiary alcohols: - tertbutyl alcohol CH3CH3OH CH3CCH3CH3CH OHPhysical Properties Inferior alcohols are liquid substances with very high boiling points, considering their molecular weight. Superior terms are solid. Alcohols have lower densities than waters, but superior than the corresponding hydrocarbons. The inferior alcohols are very soluble in water. Solubility increases with the hydroxyl group number. Chemical Properties specific to the hydroxyl group, which has a higher reactivity to the inferior terms of the series. 1. Reaction with alkaline metals alkoxides or alcoholates (alkaline hydroxyls): Alcohols have a weak acid character, their reaction with metals being used as a reducing system. ethoxide sodium H 1/2 Na O - CH - CH Na OH - CH - CH2-2 3 2 3 + + +2. Esterification reaction inorganic esters (reaction with mineral acids): CH3 OH + HOPO3H2 CH3 OPO3H2 + H2O methanol methyl phosphate organic esters (reaction with carboxylic acids) : CH3 COOH + HO CH2 CH3 CH3 COO CH2 CH3 + H2O acetic acid ethanol ethyl acetate 3. Water elimination from alcohols takes place in two modalities, function of working conditions: Intramolecular elimination of water (at warm, in the presence of sulfuric acid) forms alkenes: CH3 CH CH3 CH3 CH = CH2 + H2O I propene OH isopropanol Intermolecular elimination of water, forming an ether, (sulfuric acid is in low quantities): CH3CH2OH + HOCH2CH3 CH3CH2OCH2CH3 + H2O diethyl ether 4. Alcohol oxidation reaction primary alcohols aldehydes, secondary alcohols ketones. Tertiary alcohols are resistant to a mild oxidation, but a strong one forms many acids, with the chain braking. a. Mild oxidation of a primary alcohol: b. Strong oxidation (with potassium permanganate + sulfuric acid solution): CH3CH2CH2OHK2Cr2O7H2SO4CH3CH2COHpropanolpropanalCH3CH2CH2OH CH3CH2COOHpropionic acid c. Mild oxidation of a secondary alcohol d. Strong oxidation of a secondary alcohol C2H5C2H5CHOHC2H5C2H5CO3-pentanoldiethylketoneC2H5C2H5CH OHCH3CH2COOH CH3COOHpropionic acidacetic acid+Thiols (mercaptans) monosubstituted organic derivatives of hydrogen sulfide H2S, formula RSH for thiols and ArSH for thiophenols. Comparing with alcohols, they have lower boiling points (sulfur does not form hydrogen bonds), but have a stronger acid character, reacting with bases. The group SH, called thiol is found in biochemistry in homocysteine or cysteine. It can form sulfur bridges by oxidation, a very important process for the conformational organization of proteins, or for realization of reducing systems as cysteine cystine. SHCH2H2NCHCOOHSHCH2H2N CH COOHS S- 2HH2NCH2CH COOHCH2H2N CH COOH+cysteinecystine SH groups can be oxidized to form important derivatives as sulfine or sulfate. SH SO2-SO32-SO42-oxidation oxidation oxidationthiol sulfinate derivative sulfine sulfatederivative derivative sulfatePhenols Definition contain in molecule one or more hydroxyl groups (-OH) bound directly to a carbon atom, which belongs to the aromatic nucleus. Classification According the OH group numbers, phenols are: a. Monohydric phenols (monophenols) b. Polyhydric phenols (polyphenols) OHCH3OHOHphenolcresol o-naphtolOHHOOHOHOHOHOHresorcinol hydroquinonepyrogallolPhysical properties Phenols are solid substances, with low water solubility (the monohydric ones), easily soluble in alcohol, benzene, etc. Chemical properties Phenol chemical properties are a consequence of the reciprocal interactions between the functional group OH and the aryl radical: the acid character of OH group is increased (liberation of H ion); the substitution reactions, specific to the aromatic hydrocarbons. 1. Reaction with alkaline bases it puts in evidence the weak acid character of phenols. Salts phenoxides (phenolates). Phenols (being weak acids) can be liberated from their salts if a carboxylic acid is added to the salt solution. C6H5 - OH + NaOHC6H5 - ONa + H2Osodium phenolate2. Substitution reaction to the aromatic nucleus takes place on the ortho and para position, the OH group being a first order substituent. Phenol halogenation Phenol nitration 22 Br2-2HBrOHOHBrBro-Br-phenol p-Br-phenol++OH2OH+ 2HONO2- 2H2OOHOHNO2NO2+o-nitro-phenolp-nitro-phenol 2,4,6-Trinitrophenol (picric acid) is obtained when concentrated nitric acid is used, at high temperatures. Phenol sulfonation forms, at room temperature, o-phenol-sulfonic acid, but at 100C p-phenolsulfonic acid is obtained. OHNO2NO2O2NOH+ H2SO425oCOHSO3H+ H2OOH+ H2SO4100oCOHSO3H+ H2O3. Hydrogen addition reaction is catalytically realized (Ni) at high pressure and temperature. Cyclohexanol is formed. C6H5 OH + 3H2 C6H11-OH cyclohexanol Amines Definition. Nomenclature organic substances which contain in their molecule one or more amino functional groups: NH2, -NH, or NC=O), bound to an organic radical and a H atom aldehydes (R-CH=O), bound to two organic radicals ketones (R2C=O). The name of aldehydes is formed: By adding the suffix al to the name of the saturated hydrocarbon, having the same number of carbon atoms; By adding the name aldehyde before the name of the corresponding acid; By adding the suffix aldehyde to the root of the name of the corresponding acid. OC H3H- Ethanal - acetic aldehyde, - acetaldehyde The names of ketones are formed: - By adding the suffix one to the name of the saturated hydrocarbon, having the same number of carbon atoms; - By the name of the two radicals bound to the carbonyl group, followed by the name ketone. - Some time the trivial names are still used. OC H3C H3- Propanone, - dimethylketone, - acetone Physical properties - The first term of the aldehyde series (formaldehyde) is gaseous. - The rest of the terms and the ketones are liquid or solid substances, in normal conditions. - The inferior terms of both series are water soluble, - the solubility decreases with the increase of the molecular weight. Chemical properties The characteristic reactions of the carbonyl compounds are: the reactions of the carbonyl group and the reactions of the o-position (carbon 2) 1. Nucleophilic addition: - the carbonyl group is polarized; the electrons of the double bond are more attracted by the oxygen atom (more electronegative than the carbon atom). carbon atom has a partially positive charge and is a center for the attack of a nucleophilic agent. a. The addition of water hydrates (twin - geminal diols), which are instable and spontaneously eliminate water to regenerate the carbonyl compound: OC H3C H3C H3C H3OHOH+ H2O acetone propane-2,2-diol b. The addition of alcohols, acetals (from aldehydes) or ketals (from ketones). acetaldehyde + ethanol diethyl acetal of acetaldehyde c. Addition of hydrogen cyanide cyanohydrins (hydroxynitriles) OC H3HC H3HOC2H5OC2H5O H C2H5+ 2OC H3C H3OH C H3C H3CN+ HCNacetone acetone cyanohydrin 2. Aldol and croton condensation: - The condensation of the carbonyl group with the C-H group of a molecule having an active methylene. - That kind of group (with active methylene) is present in compounds with an acidifying group (>C=O, -COOR, -NO2) in the o-position of the C-H group. C1O C5COHH C18CHOHCOC26C27CO+aldol condensation-H2O croton condensation(carbonylic compound, o,| unsaturated)C OC H3C H3CHHHCHO CHCHOHC H3CHOCHCHC H3CHO+aldol-H2O aldehida crotonicacrotonaldehyde 3. Condensation with amines Carbonyl compounds react with ammonia or amines resulting imines or substituted imines (Schiff bases) amine aldehyde substituted imine 4. Reactions of oxidation and reduction: a. Oxidation with the formation of carboxylic acids, in the presence of KMnO4, CrO3: R-CH=O + [O] R-COOH b. Autooxidation with the formation of peracids: c. Reduction of carbonyl group to form primary alcohols (from aldehydes) or secondary alcohols (from ketones): R CHOR COO O H+ O2R CHOCH2OH+ [H] 2RR2C OR2CHOH+ [H] 2Carboxylic acids Definition. General formula found in a large variety and quantity in nature. contain the functional group carboxyl (COOH) general formula: R-COOH Under the influence of the carbonyl group, the hydrogen in the hydroxyl group is weakly bound to the oxygen atom. Therefore, carboxylic acids have a higher tendency to release protons (H+) than the corresponding alcohols, manifesting a stronger acidity. Under the influence of the hydroxyl group, carboxylic acids do not manifest the aldehyde or ketone character, determined by the presence of the carbonyl group. Nomenclature The scientific denomination o carboxylic acids is realized adding the suffix oic to the name of the hydrocarbon having the same carbon atoms number. H-COOH metanoic acid - formic acid CH3 COOH ethanoic acid - acetic acid CH3 CH2 COOH propanoic acid - propionic acid CH3 CH2 CH2 COOH butanoic acid - butyric acid CH2 = CH COOH propenoic acid acrilic acid CH3 CH2 CH2 CH2 COOH pentanoic acid - valeric acid In the case of carboxylic acids having more than one carboxyl group, their number is indicated with the prefix di-; tri-; etc. HOOC - COOH ethanedioic (oxalic) acid The position of the COOH groups is indicated using Arab numbers. HOOC CH2 COOH 1,3-propanedioic (malonic acid) HOOC(CH2)2COOH 1,4-butanedioic acid (succinic acid) HOOC(CH2)3COOH 1,5-pentanedioic (glutaric acid) HOOC(CH2)4COOH 1,6-hexanedioic (adipic acid) Classification according to the radical nature: saturated acids CH3 CH2 COOH propanoic acid unsaturated acids CH2 = CH COOH acrylic acid aromatic acids C6H5 COOH benzoic acid according to the COOH groups number: monocarboxylic acids CH3 COOH acetic acid - polycarboxylic acids HOOC COOH oxalic acid COOHCOOHCOOHCOOHortho-phtalic acid terephtalic acid Fatty acids (FA) - are components of lipids. > 70 FA (most majority having an even carbon atoms number, linear chain; there are, also, fatty acids with an odd carbon atoms number, with a branched chain, cyclic, etc. FA classification: saturated fatty acids unsaturated fatty acids (mono- and polyunsaturated) hydroxylated fatty acids cyclic fatty acids A. Saturated fatty acids: - linear chain - general formula: CH3-(CH2)n-COOH, n = 2 30 - the most frequently found: stearic acid (18C), palmitic acid (16C), miristic acid (14C) Fatty acid denomination Carbon atom number Structure Melting point C Usual Systematic Butyric n-butaneoic 4 CH3 (CH2)2 - COOH - 8,0 Capronic n-hexaneoic 6 CH3 (CH2)4 - COOH - 1.5 Caprilic n-octaneoic 8 CH3 (CH2)6 - COOH +16,5 Caprinic n-decaneoic 10 CH3 (CH2)8 - COOH +31,0 Lauric n-dodecaneoic 12 CH3 (CH2)10 - COOH +44,0 Miristic n-tetradecaneoic 14 CH3 (CH2)12- COOH +53,8 Palmitic n-hexadecaneoic 16 CH3 (CH2)14- COOH +62,5 Stearic n-octadecaneoic 18 CH3 (CH2)16 - COOH +69,6 Arahidic n-eicosaneoic 20 CH3 (CH2)18 - COOH +71,6 Behenic n-docosaneoic 22 CH3 (CH2)20 - COOH +80,3 Lignoceric n-tetracosaneoic 24 CH3 (CH2)22 - COOH +84,5 B. Unsaturated fatty acids monounsaturated (with a single double bond) Cn:m example: oleic acid (C18:9) found mostly in vegetals; the cis form is liquid, the trans form is denominated elaidic acid (solid; synthetic product); palmitoleic acid (C16:9) CC(CH2)7CH3(CH2)7COOHHHCC(CH2)7CH3(CH2)7COOHHHoleic acid elaidic acid polyunsaturated (with many, isolated double bonds) Example: linoleic acid (C18:9,12); linolenic acid (C18:9,12,15); arahidonic acid (C20:5,8,11,14) they cannot be synthesized by human organisms, their intake being indispensable (ESSENTIAL FATTY ACIDS) Their deficiency produces retarded development, hair loosing, reproduction troubles. They are basic components of cellular and mitochondria membranes. They are prostaglandins precursors. 18 13 12 11 10 9 1 CH3 - (CH2)4 CH = CH CH2 CH= CH (CH2)7 COOH e6 linoleic acid CH3 CH2 CH = CH - CH2 - CH=CH - CH2 - CH=CH - (CH2)7 COOH e3 linolenic acid CH3 (CH2)4 (CH=CH CH2)3 CH = CH (CH2)3 COOH e6 arahidonic acid C. Hydroxylated fatty acids They are rare and contain a functional secondary hydroxyl group (- OH) in the saturated or unsaturated chain. Example: cerebronic acid (24C), hydroxynervonic acid (24C + a double-bond) are found in cerebrozides Physical properties Saturated, acyclic, monocarboxylic acids - liquid (the inferior terms) and solid (superior terms). The inferior terms are water soluble, but solubility decreases as the molecular weight increases. The superior terms are soluble only in organic solvents. Polycarboxylic acids are solid. Their water solubility is much higher to the odd carbons number terms comparing with even carbon numbers terms, and decreases with the molecular weight. CH3 (CH2)21CHCOOHOHCH3 (CH2)7CH COOHOHCH CH(CH2)12cerebronic acid hydroxynervonic acid Chemical properties Organic acids are the final products of many oxidizing reactions and have some chemical stability. 1. Common properties with inorganic acids (ionization in water solution, reaction with active metals, with basic oxides, with bases, etc.). a. Carboxylic acids are weak acids b. Synthesis of carboxylic acid salts: With hydroxides CH3 COOH + NaOH CH3 COO-Na+ + H2O sodium acetate with basic oxides 2CH3COOH + K2O 2CH3COO-K+ + H2O with active metals 2CH3COOH + 2Na 2CH3COO-Na+ + H2 CH3 - COOH + H2O CH3 - COO- + H3O +acetic acidacetate ion 2. Characteristic reactions of carboxylic acids anhydrides, esters, amides, nitriles, halides. a. Reaction with ammonia Ammonium salts, which dehydrate partially, at warm, forming amides. Total dehydration, in phosphorus pentaoxide presence, forms nitriles. acetate ammonium acid aceticCOONH - CH NH COOH - CH4 3 3 3 +CH3 - COONH4 partial dehydrationtoC, -H2OCH3 - CO - NH2acetamideCH3 - COONH4total dehydrationP2O5, -H2OCH3 - CNacetonitrileb. Reaction with amines forms an amidic bond: CH3 COOH + CH3 NH2 CH3 CO NH CH3 + H2O N-methyl-acetamide These types of bonds are found in complex lipids (sphingolipids). c. Reaction with alcohols (esterification) takes place in acid catalysis esters. d. Obtaining of carboxylic acid anhydrides CH3 - COOH + C2H5 - OH CH3 - CO - OC2H5 + H2Oethyl acetateCH3 - COOH + HOOC - CH3CH3 -COCH3 - COOacetic anhydrideCH3 - COOH + HOOC - C6H5CH3 -COC6H5 - COOmixt anyidrideacetic - benzoic Carboxylic acid derivatives have a common property: they regenerate by hydrolysis the carboxyl group 1. Ester hydrolysis in acidic medium: 2. Acid anhydride hydrolysis: 3. Amide hydrolysis: 4. Nitrile hydrolysis CH3-CN + 2H2O CH3-COOH + NH3 CH3 - CO - OC2H5 + H2O H+CH3 - COOH + C2H5 - OH acetic acid ethanol ethyl acetatelCH3 - COCH3 - COO+ H2O2 CH3 - COOHacetic anhydride acetic acidC6H5 - CO - NH2 + H2OtoCC6H5 - COOH + NH3benzamide benzoic acidOrganic derivatives of phosphorus The most spread phosphorus combinations are: esters of phosphoric, diphosphoric and triphosphoric acids. Phosphoric acid H3PO4 - weak acid - It has three ionization steps, the first one being the easiest one. - The main phosphoric acid combinations are phosphates, (esters) obtained from the combination with an alcohol. POOHOH HOOOCH2OHOHOHOHOHOHOHOHCH2OHO POOHOH+H2O+ H3PO4glucose glucose-1-phosphate Polyphosphoric acids are obtained by condensation of phosphoric acid molecules. 2H3PO4 H4P2O7 + H2O Three phosphoric acid molecules form triphosphoric acid HO - P - O - P - OHO OOH OHpyrophosphoric acid HO - P - O - P - O - P - OHO OOH OHOOH Polyphosphoric acids are parts of molecules rich in energy, type XTP, where X represents a purine or pyrimidine nucleozide These molecules are macroergic, which means they store a high quantity of energy as phosphate anhydride bonds. This energy can be easily liberated when the bond is hydrolyzed. NONNNNH2OH OHCH2HO - P ~ O - P ~ O - P ~ OOH OH OHO O OAdenosine triphosphate ATP Heterocycles A. Contain one or more heteroatoms in their cycles. For example: cyclic esters of glycine, cyclic anhydrides of dicarboxylic acids, cyclic secondary amines, monosaccharides. These compounds do not behave chemically very differently from the acyclic compounds with a similar structure. B. Heterocyclic combinations, poor in hydrogen, which are more similar to benzene, having an aromatic character. The main heteroatoms found in heterocyclic combinations with an aromatic character are nitrogen, oxygen, sulfur. NC HC HCHCHCHOC HCHCHCHSC HCHCHCHNHC HCHCHCHNHC HN CHCHNHCHCHCHC HC HCHOC HC HCHCHCH2NC HNCHCHCH NNNNNOpyridinefuran thiofenpyrolimidasolindol pyranphenoxasinepyrimidinepurine