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ORGANIC CHEMISTRY
1.1 Functional Groups
are used to identify compounds but also to explain properties like solubility, melting & boiling points, etc.
there are many different functional groups but they contain one of 3 main components
i.e.
Carbon-Carbon Bonds
C-C single bonds are strong covalent bonds and are not very reactive
C=C and CΞC are more reactive and their 2nd and 3rd bonds are more easily broken
this allows these parts of a compound to be the sites where reactions occur
Single Bonds Between C & more Electronegative Bonds
where there is an unequal attraction of the electrons the bond is polar e.g. between C and a more electronegative atom
the C atom becomes more +ve and the O,N or halogen atom is more –ve
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an increase in polarity increases intermolecular forces which in turn increases the melting & boiling points
O-H and N-H bonds form bonds with special properties and they can form H-bonds with other OH groups, they increase intermolecular attractions but also enables these molecules to dissolve in polar solutes & solvents
“like dissolves like”
Double Bonded Carbon & Oxygen
this double covalent bond has 4 electrons being shared with ALL 4 electrons being more strongly attracted to the O atom
this bond is very polar with an accompanying increase in melting & boiling points and increased solubility in polar solvents
1.2 Hydrocarbons
alkanes- single C-C bonds, if all C’s have H’s attached, molecules
are called saturated hydrocarbons alkenes- have one or more C=C double bonds alkynes- have one or more CΞC triple bonds
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alkenes & alkynes are called unsaturated hydrocarbons because they have fewer than the maximum possible number of H atoms
can form either a straight chain or a cyclic (ring) structure
hydrocarbons which are attached to the main structure are called alkyl groups and are named according to the number of carbons
a 4th group are the aromatic hydrocarbons which have a unique ring structure
simplest is benzene and all others are derivatives of benzene
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Note: When naming propyl & butyl groups we have to consider how these groups attach onto the parent chain
i.e. when an alkyl group has 3 or more C atoms the group can attach either at an end C atom or at a middle C atom (see Fig.4 & 5)
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Aromatic Hydrocarbons
benzene ring usually considered to be the parent chain and attached alkyl groups are the branches
if a methyl group is attached, the molecule is called methylbenzene and we don’t need to assign a number
when we have 2 or more alkyl groups attached we need to use numbers (again numbering so that we have the lowest numbers)
Note: a) also known as ortho- or o-diethylbenzene b) also known as meta- or m-diethylenebenzene c) also known as para- or p-diethylenebenzene
when an aromatic molecule is too difficult to name sometimes we would consider the benzene ring as the attached branch and not the parent molecule
when the benzene ring is the attached branch it is called a phenyl group
(see Fig. 9 on page 20)2-phenylbutane or s-butylbenzene
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Physical Properties of Hydrocarbons
essentially nonpolar because they are made of C & H, atoms with similar electronegativities
main intermolecular forces are Van der Waals forces (electrons of one molecule with the nucleus of another)
because these forces are weak, molecules are easily separable from one another
small molecules have fewer electrons and weaker Van der Waal forces and therefore have lower boiling & melting points when compared to larger molecules
due to low polarity hydrocarbons generally have low solubility in polar solvents, like water
however, they will be good solvents for other nonpolar molecules
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1.3 Reactions of Hydrocarbons
alkanes because of their C-C bonds are relatively unreactive due to their being difficult to break
they do participate in combustion reactions, making them useful as fuels
although C-C bonds are difficult to break, the hydrogen atoms can be substituted by halogens in substitution reactions i.e. with F2, Br2, or Cl2
the product is referred to as a halogenated alkane, which are referred to as an organic family called alkyl halides
as the reaction above proceeds the concentration of bromoethane increases and bromine will react again to form 1,2-dibromoethane
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Reactions of Alkenes & Alkynes
both exhibit greater reactivity than alkanes i.e. if reacted with Br2 the reaction will be fast and will occur at room temperature
both undergo a characteristic reaction called an addition reaction, where atoms are added to the molecule with no loss of H atoms
addition reactions can involve halogens, H, hydrogen halides,and water, given the right conditions
Examples:
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common prefixes for functional groups include;
when molecules consisting of 2 identical atoms (H2) are added to a double bond only 1 possible product is formed, i.e a H atom gets added to each side of the double bond
but when molecules of a non-identical atom is added, 2 different products may form e.g.
experiments have shown that only one main product is formed which leads us to Markovnikov’s Rule….”the rich get richer”
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(see sample problem on page 26)
Reactions of Aromatic Hydrocarbons
although aromatic hydrocarbons are unsaturated, they do not undergo addition reactions except under extreme conditions
they do undergo substitution reactions and in fact the H atoms are more easily replaced than in alkanes
the reactivity of aromatic hydrocarbons are in between the alkanes & alkenes
Examples:
in reaction (b) further reaction of bromobenzene with Br2 results in substitution of another Br, resulting in 3 possible isomers of dibromobenzene
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i.e.
relatively low reactivity of benzene indicates that benzene is fairly stable and that the bonds in benzene are different than in the double & triple bonds in alkenes & alkynes
in another substitution reaction, benzene reacts with nitric acid in the presence of sulphuric acid to form nitrobenzene
benzene can also react with alkyl halides (R-X) in the presence of an aluminum halide catalyst (AlX3) ; alkyl group attaches to the benzene displacing an H atom on the ring
these products can undergo further reactions where one can design and synthesize compounds where the desired groups are attached in specific positions on the ring
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(see sample problem on page 29)
1.4 Organic Halides
organic halides are hydrocarbons with attached halogen atoms
e.g. Freon (chlorofluorocarbons), Teflon (polytetrafluoroethene), etc.
Naming Organic Halides
consider the halogen atom as an attachment on the parent chain
halogen name is shortened to its root namei.e. Fl=fluoro-, Cl=chloro-, etc.
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Properties of Organic Halides
halogens are more electronegative so the organic halide molecules are more polar i.e. C-halogen bonds polarity > C-H bonds
therefore the intermolecular forces are stronger with halide containing molecules and they have higher boiling points and being more polar can dissolve in polar solvents
compounds may contain 1,2, or 3 halogens per molecule the more halogen atoms per molecule, the more polar the
molecule, the higher the boiling point etc.
Read the Cost of Air Conditioning on page 34.Preparing Organic Halides
can be produced by halogenation reactions
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similarly, if we wanted to produce a halide of a benzene ring, we would arrange a substitution reaction with a halogen
Preparing Alkenes from Alkyl Halides: Elimination Reactions
alkyl halides can eliminate a H atom and a halogen atom from adjacent C atoms resulting in the formation of a double bond and therefore an alkane in an elimination reaction
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1.5 Alcohols and Ethers
structurally similar except that alcohols have the general form R-O-H and ethers have the general form R-O-R, where R represents alkyl groups
properties are generally due to the polar OH groups and other non-polar groups
Alcohols
Naming Alcohols
IUPAC rules say that any R-OH should end with the suffix “–ol” which is added to the parent chain i.e. methane with an OH is called methanol
an alcohol with 2 carbons is called ethanol and so on….. when an alcohol has more than 2 C’s or OH groups we
number the C atoms to locate the OH groups the 2 isotopes of C3H7OH are;
2-propanol is also known as isopropanol, i-propanol or isopropyl
alcohol
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1°, 2° and 3° Alcohols
can also be classified by the type of C where the –OH is attached
since C can form 4 bonds, the C atom can be attached to 1, 2 or 3
alkyl groups resulting in 1°, 2° and 3° alcohols example 1-propanol is a primary alcohol, 2-propanol is a secondary alcohol, while 2-methyl-2-propanol is a tertiary alcohol
important for predicting reactions because the reactions are determined by the availability of H atoms or alkyl groups in key positions
Polyalcohols
alcohols containing more than 1 OH group are called polyalcohols
the suffixes –diol and –triol are added to the entire alkane name to indicate the number of OH groups
e.g. 1,2-ethanediol (ethylene glycol) found in antifreeze
the OH groups can also be considered as an added group to a
parent chain and has the prefix –hydroxy
i.e. 1,2,3-propanetriol is also called 1,2,3-trihydroxypropane
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Cyclic Alcohols
cyclic compounds with OH groups attached are called cyclic alcohols
many compounds are known by their common names which end in –ol i.e. menthol, cholesterol
aromatic compounds with attached OH groups compose the aromatic alcohol group
simplest in this group is hydroxybenzene or phenol phenol is a colourless solid, slightly soluble in water
(due to OH group), used in industrial preparation of plastics, drugs, dyes & weedkillers
when naming cyclic or aromatic alcohols the OH group may be considered as a group attached to the parent ring
i.e. phenol is also named hydroxybenzene a benzene ring with 2 adjacent OH groups would be
named 1,2-dihydroxybenzene
(see sample problems and examples on pages 40 & 41)
Properties of Alcohols
boiling points of alcohols are higher than those of their parent alkanes due to their OH groups which make them more polar and gives them the capability of forming H bonds
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simple alcohols are also more soluble in water for the same reason
in longer alcohols the hydrocarbon portion is nonpolar making them good solvents for nonpolar molecular compounds, as well
Reactions Involving Alcohols
a) Hydration Reactions
many alcohols are prepared by addition reactions of water to unsaturated hydrocarbons
this type of addition reaction is called a hydration reaction (using Markovnikov’s rule)
b) Combustion of Alcohols
c) Elimination Reactions
reverse of a hydration reaction under certain conditions alcohols decompose to produce
alkenes and water this reaction is catalyzed by concentrated sulphuric acid called a dehydration reaction
(see sample problems on pages 43 & 44)
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EthersProperties of Ethers
structure similar to water H-O-H and alcohols R-O-H only in ethers, structure is R-O-R (where R=alkyl groups)
alkyl groups may be identical or different there are no OH bonds in ethers so they do not form
hydrogen bonds C-O bonds are polar and the v-shape of the C-O-C group
make ether molecules more polar than hydrocarbons intermolecular attractions between ether molecules are
stronger than hydrocarbons but weaker than those in alcohols, which is seen in Table 2 by looking at the boiling points
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ethers are good solvents for organic reactions because they mix readily with both polar and non-polar substances
C-O bonds are polar so ethers can dissolve polar substances while their alkyl groups allow them to dissolve non-polar substances
C-O bonds are hard to break, making ethers unreactive another property of a good solvent
Naming Ethers
named by adding –oxy to the prefix of the smaller hydrocarbon group and joining it to the alkane name of the larger hydrocarbon group
example:CH3-O-C2H5 is methoxyethane NOT ethoxymethane
names are sometimes derived from the 2 alkyl groups followed be the word ether
example: methoxyethane would be methyl ethyl ether
when the 2 alkyl groups are the same di- is used i.e. ethoxyethane is diethyl ether
Preparing Ethers from Alcohols: Condensation Reactions
ethers are formed when 2 alcohols react eliminating a molecule of water
this type of reaction where water is released is called a condensation reaction
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(see sample problem on page 47)
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Aldehydes & Ketones
aldehydes and ketones are closely related in that they both contain a carbonyl group (C=O)
in ketones, the carbonyl group is attached to 2 alkyl groups and no H groups
in aldehydes, the carbonyl group is attached to at least 1 H atom and is also attached to either another H atom or an alkyl group
i.e. in ketones the C=O is in the middle and in aldehydes the C=O is at the end of the carbon chain
Naming Aldehydes & Ketones
aldehydes are named by taking the parent alkane name, dropping the e and adding the suffix -al
the simplest aldehydes is HCHO, has only 1 C and therefore the parent chain name is methane and as an aldehyde the name becomes methanal (formaldehyde)
2 carbon aldehyde would be named ethanal (acetaldehyde),etc.
ketones are named by replacing the e ending of the alkane with
-one the simplest ketone is propanone, CH3COCH3 (acetone)
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if a ketone has 5 or more carbons in the carbon chain containing the carbonyl group than we need to specify the location of the carbonyl group
Example: in 2-pentanone the carbonyl group is the second carbon in the chain
(see the sample problem on pages 50 & 51)
Properties of Aldehydes & Ketones
aldehydes & ketones have lower boiling point’s than analogous alcohols and are less soluble in water as they don’t have OH groups and don’t participate in H bonding
C=O is a strongly polar group so that they are both more soluble in water than are hydrocarbons
Are good solvents because they will mix with both polar and non-polar substances
Preparing Aldehydes and Ketones from Alcohols: Oxidation Reactions
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oxidation reaction in organic chemistry implies a gain of oxygen or a loss of hydrogen
in the following reactions oxygen is supplied by compounds called oxidizing agents like H2O2 (hydrogen peroxide), K2Cr2O7 (potassium dichromate) and KMnO4 (potassium permanganate)
the (O) removes 2 H atoms, one from the OH and the other from the “R” group resulting in the formation of a C=O group + an H2O
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From Aldehydes & Ketones to Alcohols: Hydrogenation Reactions
the carbonyl group can undergo an addition reaction with H but not other reactants
high heat, pressure and a catalyst are needed for this hydrogenation reaction
the reaction adds H to the C=O which results in an OH group which produces an alcohol
Note: due to the type of groups attached to the carbonyl C atom, aldehydes always produce primary alcohols while ketones always produce secondary alcohols
(see sample problems on pages 55 & 56)
Carboxylic Acids & Esters
organic acids have a carboxyl functional group –COOH and are called carboxylic acids
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like inorganic acids, carboxylic acids can react with OH containing compounds to form an organic “salt” called an ester
Carboxylic Acids
are generally weak acids, are found in citrus fruits, crab apples, rhubarb, and other foods known by their sour tangy taste
carboxylic acids also have distinct odours that can be used in law enforcement
Naming Carboxylic Acids
the carboxyl group -COOH combines the C=O and OH groups that we are familiar with already
IUPAC name is formed by taking the name of the alkane or alkene with the same number of C atoms as the longest chain in the acid
(don’t forget to include the C in the –COOH group) the ending –e in alkane or alkene is changed to –oic and
adding the word acid
Examples:
methane….methanoic acid (HCOOH)methanoic acid is commonly called formic acid ethane…ethanoic acid (CH3COOH) commonly called acetic acid (makes vinegar taste sour)
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simplest aromatic acid is phenylmethanoic acid (benzoic acid)
some acids contain multiple COOH groups i.e. oxalic acid
(2 COOH groups bonded to each other)
when naming acids with multiple COOH groups, use –dioic acid when COOH’s are at each end of the parent chaine.g HOOC-CH2-COOH is propanedioic acid
when more COOH groups are present the COOH groups can be named as groups on the parent chain and are not counted as part of the parent chain
(see sample problem on page 60)
Properties of Carboxylic Acids
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due to C=O and OH groups in carboxyl groups these molecules are polar and can form hydrogen bonds with each other and water molecules
smaller acids have similar solubility to alcohols but larger ones are relatively insoluble
carboxylic acids have the properties of acids and can react organic “bases” to form “salts”
due to intermolecular attractions between the carboxyl functional groups the melting points are higher than their corresponding hydrocarbons
Preparing Carboxylic Acids
when an alcohol is mildly oxidized an aldehyde is produced and further oxidation results in the formation of a carboxylic acidi.e.
(O) in these reactions is supplied by an oxidizing agent
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using an oxidizing agent that changes colour is that basis of the breathalyser test
(see sample problems on pages 62-63)
From Carboxylic Acids to Organic “Salts”: Esterification
carboxylic acids can react in neutralization reactions in reactions with alcohols (where the alcohol acts as an
organic base) this reaction forms an ester and water
Esters
responsible for the colours and odours of plants (table 2 p. 64&65)
generally have the structure of
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Naming and Preparing Esters
name has 2 parts first part from the alkyl group from the alcohol used and
the second part is from the acid the second part also changes its suffix from –oic to –oate
e.g.
the general formula can be written as RCOOR1
RCO from the carboxylic acid while the OR1 comes from the alcohol
i.e. for an ester the acid is the first part drawn but is the 2nd part of the name
(see sample problem on p. 65&66)Properties of Esters
compared to a carboxylic the functional group is similar but is missing the OH group
i.e. the –OH is replaced by an –OR group therefore esters are less polar, less soluble in water and
have lower melting and boiling points than their parent acids
acidity of carboxylic acids is from the H on the OH group, esters missing the OH group are not acidic
Reactions of Esters: Hydrolysis
when an ester is treated with an acid or base, it will split into its acid and alcohol components
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this type of reaction is called hydrolysis
saponification is a reaction where an ester is hydrolyzed basis of soap making where fats and oils (esters of long chain acids) are heated with a strong base which causes a hydrolysis reaction and the sodium salts of the acids are “soap”
Amines and Amides
these are compounds that contain nitrogen, as well as, carbon, hydrogen, oxygen, etc.
amines are like NH3 with 1,2, or 3 of its H’s replaced with alkyl groups and are classified as 1°, 2° or 3°
amines are organic bases and can react with carboxylic acids to form nitrogen-containing (nitrogenous) organic salts called “amides”
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amides have the functional group –CON, which can be found in proteins, etc.
Amines
when once living things break down to form amines which have an unpleasant odour e.g. smell of rotting fish due to a mixture of amines
decomposing animal tissue produce amines called putrescine and cadaverine
Naming Amines
can be named in 2 ways;1. as a nitrogen derivative of an alkane (IUPAC way)
e.g. CH3NH2 would be aminomethane or2. as an alkyl derivative of ammonia e.g.
methylamine
Examples:
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if there are 2 amino groups, they are called diamines so IUPAC name for cadaverine is 1,5-diaminopentane
a shortcut is to use N to show the substituted groups on the N atom of the amino group i.e see last 2 molecules above
an alternative naming system is where the name implies a derivative of ammonia
see 2° amine above, which has 2 alkyl groups on the N atom, a methyl and a butyl which is given the name butylmethylamine
see 3° amine above, which has 3 methyl groups around the central N atom, which is given the name trimetylamine
(see sample problems on page 71)
Properties of Amines
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amines have higher boiling points and melting points than hydrocarbons of the same size and smaller amines are soluble in water due to N-C and N-H both of which are polar
when N-H bonds are present, hydrogen bonding can occur with water which explains the high solubility of amines in water
N-H bonds are less polar than O-H so amines will boil at lower temperature
Preparing Amines
can be prepared by reaction of ammonia (a weak base) with an alkyl halide
this reaction if left to continue can produce a mixture of 1°, 2°, 3° amines i.e.
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these 3 components can be separated by fractional distillation due to their different boiling points
Amides
similar to esters but here we have a N atom replacing the O atom
the amide functional group consists of a carboxyl group attached to an N atom
Naming and Preparing Amides
carboxylic acids react with ammonia or with 1° and 2° amines (organic bases) to produce amides (organic salts)
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both of these reactions are condensation reactions and water is formed
again, the amide functional group is carbonyl group attached to a N atom
N makes 2 more bonds to either H atoms or alkyl groups
tertiary amines will not undergo the above reaction which needs a H atom on the amine
note the similarity between the synthesis of an ester and the synthesis of an amide from a primary amine below
naming amides is similar to naming esters esters end in –oate while amides end in –amide name of an amide is made up of 2 parts:
1. first part from the amine in the example above the amine is methylamine
so name begins with methyl 2. second part comes from the name of the acid in the example above butanoic acid…oic is
dropped and amide is added…butanamide the name therefore is methyl butanamide, as with esters
the name is separated into 2 words when there are 1 or more alkyl groups attached to the N
atom in the amide linkage we use the letter N to clarify the location of the group i.e.
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(see sample problem on page 75)
Properties of Amides
amides are weak bases, insoluble in water low molecular weight amides are slightly soluble in water
because of the hydrogen bonding taking place between the amides` polar N-H bonds and the water molecules
amides whose N atoms are bonded to 2 H atoms have higher melting and boiling points than amides that have more attached alkyl groups
explained by increased hydrogen bonding
Reactions of Amides
like esters, amides can be hydrolyzed in acidic or basic conditions to produce a carboxylic acid and an amine
reverse of formation reactions of amides
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(See sample problem on page 77)
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