Ch5 Organic Chemistry

transcript

CHAPTER 5: ORGANIC CHEMISTRY

5.1 Alkanes

5.2 Alkenes

5.3 Aromatic Hydrocarbons

5.4 Alcohols

5.5 Haloalkanes (Alkyl Halides)

5.6 Carbonyl Compounds

5.7 Carboxylic Acids

What Is Organic Chemistry?

Organic chemistry is a branch of chemistry that focuses on compounds that contain carbon

• except CO, CO2, carbonates, and carbides

Even though organic compounds only contain a few elements, the unique ways carbon atoms can attach together to form molecules leads to millions of different organic compounds

Tro: Chemistry: A Molecular Approach, 2/e

What’s So Special About Carbon?

Carbon atoms can do some unique things that other atoms cannot Carbon can bond to as many as four other atoms Bonds to carbon are very strong and nonreactive Carbon atoms can attach together in long chains Carbon atoms can attach together to form rings Carbon atoms can form single, double, or triple bonds

What’s Special About Organic Compounds?

Organic compounds tend to be molecular

Mainly composed of just six nonmetallic elements• C, H, O, N, S, and P

Compounds found in all three states• solids, liquids, and gases• solids tend to have low melting points

Solubility in water varies depending on which of the other elements are attached to C and how many there are• CH3OH is miscible with water; C10H21OH is insoluble

Carbon Bonding

Carbon forms four bonds When C has four single bonds, the

shape is tetrahedral When C has one triple + one single

or two double bonds, the shape is linear

When C has two single + one double bond, the shape is trigonal planar

Hydrocarbons Hydrocarbons contain only C and H

• aliphatic or aromatic Insoluble in water

• no polar bonds to attract water molecules Aliphatic hydrocarbons

• saturated or unsaturated aliphatics• saturated = alkanes, unsaturated = alkenes or alkynes

• may be chains or rings• chains may be straight or branched

Aromatic hydrocarbons

alkanes

Alkanes

Saturated hydrocarbons (Aliphatic) • Hydrocarbons – Contain only C and H atoms.• Saturated – Only single bonds. • Aliphatic – “Fat” like. • Can be acyclic (no rings) or cyclic

(cycloalkanes).

Table 5.1 Numerical Roots for Carbon Chains and Branches

Number of C atomsRoots

PREFIX + ROOT + SUFFIX

Physical Properties of n–Alkanes

Physical Properties of Alkanes

Alkanes• Solubility – “Like dissolves like” • Alkanes are nonpolar, hydrophobic• They are soluble in nonpolar solvents and

insoluble in water.

Ways of depicting an alkane.

Formulas Molecular formulas : shows what kinds

of atoms are in the molecule, but not how they are bonded together

Structural formulas shows the bonding pattern in the molecule

AlkanesMethane, CH4

Ethane, CH3CH3

AlkanesPropane, CH3CH2CH3

Butane, CH3CH2CH2CH3

Condensed Structural Formulas

Elements listed in order• central atom with attached atoms

Follow normal bonding patterns• shows position of multiple bonds

() used to indicate more than one identical group attached to same previous central atom• unless () group listed first in which case

attached to next central atom

Example – Write the structural and condensed formula for the straight chain alkane C8H18

Connect the C atoms in a row• Carbon backbone

Add H to complete four bonds on each C.• middle C gets 2 Hs • end C gets 3 Hs

The condensed formula has the H attached to each C written directly after it

Alkanes

Pentane, CH3CH2CH2CH2CH3

Hexane, CH3CH2CH2CH2CH2CH3

Heptane, CH3CH2CH2CH2CH2CH2CH3

Octane, CH3CH2CH2CH2CH2CH2CH2CH3

Nonane, CH3CH2CH2CH2CH2CH2CH2CH2CH3

Decane, CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Carbon Skeleton Formulas

Each angle, and beginning and end, represents a C atom H omitted on C

• included on functional groups Multiple bonds indicated

• double line is double bond, triple line is triple bond

Isomerism

Isomerism – The phenomenon whereby certain chemical compounds have structures that are different although the compounds possess the same elemental composition.

Isomers – Two or more chemical substances having the same elementary composition and molecular weight but differing in structure.

Structural isomers are isomers are also called Constitutional isomers

Isomerism

Consider C4H10

These structures are constitutional isomers

H HH H

Normal Butane Isobutane

Rotation about a Bond Is Not Isomerism

Possible Structural Isomers of Alkanes

fill in the H to give each carbon four bonds

Example 20.1: Write the structural formula and carbon skeleton formula for the 5 structural isomers of C6H14

Alkyl Groups

Names and Formulas of Alkyl Groups:

Formula Name Formula Name

CH3- methyl CH3CH2CH2CH2- butyl

CH3CH2- ethyl (CH3)2CHCH2- isobutyl

CH3CH2CH2- propyl CH3CH2CH(CH3)- sec-butyl

(CH3)2CH- isopropyl (CH3)3C- tert-butyl

AlkanesNames and Formulas of Alkyl Groups:

Primary (1o) carbon

Secondary (2o) carbon

Tertiary (3o) carbon

IUPAC Rules for Naming Alkanes Select the longest continuous chain of carbon

atoms as the parent compound. Number the carbon atoms in the parent carbon

chain starting from the end closest to the first carbon atom that has an alkyl or other group.

Name the alkyl group and designate the position on the parent carbon chain by a number.

When the same alkyl group branch chain occurs more than once, indicate this repetition by a prefix (di-, tri-, tetra-, and so forth).

When several different alkyl groups are attached to the parent compound, list them in alphabetical order.

Example 1

CH2 CH

CH3CH2CH3parent alkane

alkyl group

3-methylpentane

CH2 CH

alkyl group

3-methylpentane

Example 1

CH2 CH

alkyl group

3-methylpentane

Example 1

CH2 CH

alkyl group

2-methylpentane

Example 2

1 2 3 4CH3 CH CH CH3

CH3 CH3

2,3-dimethylbutane

CH3 CH2 C CH3

2,2-dimethylbutane

Example 2

CH3 CH3

2,3-dimethylbutane

CH3 CH2 C CH3

2,2-dimethylbutane

Example 2

CH3 CH3

2,3-dimethylbutane

CH3 CH2 C CH3

2,2-dimethylbutane

Example 2

CH3 CH3

2,3-dimethylbutane

CH3 CH2 C CH3

2,2-dimethylbutane

Example 3

CH3 CH CH2 CH CH CH CH3

2,3,4,6-tetramethylheptane

Example 3

Note: Number the chain so that the substituents get the lowest possible numbers.

Example 3

Note: Number the chain so that the substituents get the lowest possible numbers.

Example 4

CH3 CH CH2 CH2 CH3

CH2 CH312

3 4 5 6

3-methylhexane

Examples

Caution: Be careful to choose the longest chain as the parent alkane.

CH3 CH CH2 CH2 CH3

CH2 CH312

3 4 5 6

3-methylhexane

Examples

Caution: Be careful to choose the longest chain as the parent alkane.

CH3 CH CH2 CH2 CH3

CH2 CH312

3 4 5 6

3-methylhexane

Examples

123456CH3 CH2 CH2 CH2 C CH CH CH3

CH3CH3

CH2 CH3

3-chloro-4-ethyl-2,4-dimethyloctane

Examples

CH3CH3

CH2 CH3

Example 4

Note: Substituents are listed in alphabetical order.

CH3CH3

CH2 CH3

Draw the Compounds

3-ethylpentane

2,2,4-trimethylpentane

Draw the Compounds

3-ethylpentane

CH3 CH2 CH2 CH2 CH3

1 2 3 4 5

CH2 CH3

Draw the Compounds

3-ethylpentane

1 2 3 4 5CH2 CH3CH3 CH2 CH

CH2 CH3

Draw the Compounds

3-ethylpentane

1 2 3 4 5CH2 CH3CH3 CH2 CH

CH2 CH3

CH3 CH2 CH2 CH2 CH3

CH3 CH3

1 2 3 4 5

Draw the Compounds

3-ethylpentane

1 2 3 4 5CH2 CH3CH3 CH2 CH

CH2 CH3

CH2 CH2 CH3

1 2 3 4 5

Naming of Cycloalkanes

H2C CH2

CH2H2C CH2

H2C CH2

CH2H2C CH2

Cyclopropane

Cycloalkanes

H2C CH2

CH2H2C CH2

Cyclopropane

Methylcyclohexane

Cycloalkanes

H2C CH2

CH2H2C CH2

Cyclopropane

Methylcyclohexane

(CH2)5CH3

H2C CHCH2

CH2CH2CH2CH2CH2CH3

1-Cyclobutylhexane

Hexylcyclobutane

Cycloalkanes

1-Ethyl-2-methylcyclohexane

CH2H2C CH

Name the Following Compounds

Methylcyclopropane 1,1-Dimethylcyclohexane

1,2-Dimethylcyclopentane 3-Cyclopropylpentane

Geometric Isomerism in Cycloalkanes

Geometric isomers have the same molecular formula but a different orientation in space that cannot be overcome by rotation around a bond.

1,2-Dimethylcyclopentane:

H3C CH3

1,2-dimethylcyclopentane

cis-1,2-dimethylcyclopentane trans-1,2-dimethylcyclopentane

Geometric isomers have the same molecular formula and the same order of attachment but a different orientation in space that cannot be overcome by rotation around a bond.

H3C CH3

1,2-dimethylcyclopentane

cis-1,2-dimethylcyclopentane trans-1,2-dimethylcyclopentane

Name the following compounds:

CH3H3C

Geometric Isomerism in CycloalkanesName the following compounds:

CH3H3C

trans-1,2-dimethylcyclopropanecis-1-tert-butyl-4-methylcyclohexane

Reactions of Hydrocarbons

All hydrocarbons undergo combustion

Combustion of butane

2 CH3CH2CH2CH3(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)

Alkane Reactions

Substitution Reaction

• replace H with a halogen atom

• initiated by addition of energy in the form of heat or ultraviolet light

• to start breaking bonds

• generally get multiple products with multiple substitutions through chain reactions

Chlorination of Methane Methane reacts with chlorine in the presence of heat or

light to produce a mixture of products through a sequence of substitution reactions in which the H atoms are successively replaced by Cl atoms.

CH4 + Cl2 heat or light CH3Cl + HCl

CH2Cl2 + HCl

CH3Cl , chloromethane Cl2

CH2Cl2 , dichloromethane CHCl3 + HCl

CHCl3 , trichloromethane Cl2

CCl4 , tetracloromethane CCl4 + HCl

Free Radical Substitution

The breaking of a covalent bond so that each atom retains one of the shared electrons will produce two free radicals.

Free radicals are very reactive. They are intermediates in reaction mechanism.

The substitution reactions of alkanes follow the free radical mechanism, which involved three major steps:

1. Initiation: Initial production of free radicals

2. Propagation: Free radicals attack molecules to produce another free radical

3. Termination: Two free radicals combine to form a molecule

Mechanism of Free Radical substitution1. Chlorination of methane starts with the production of Cl free radicals (Cl

atoms)

Cl2 hv Cl∙ + Cl∙

2. The Cl free radical attacks the CH4 molecule to give a methyl free radical, CH3∙ and HCl.

CH4 + Cl∙ CH3∙ + HCl

The methyl free radical reacts with Cl2 to give chloromethane.

CH3∙ + Cl2 CH3Cl + Cl∙

Subsequent reactions produce various alkyl free radicals which lead to the formation of the other substitution products.

3. Reaction stops when free radicals combine

CH3∙ + Cl∙ CH3Cl

CH3∙ + CH3∙ CH3CH3 (by product)

Unsaturated Hydrocarbons

Unsaturated hydrocarbons have one or more C=C double bonds or CC triple bonds

Unsaturated aliphatic hydrocarbons that contain C=C are called alkenes• the general formula of a monounsaturated chain alkene is

Unsaturated aliphatic hydrocarbons that contain CC are called alkynes• the general formula of an alkyne with one triple bond is

CnH2n−2

Alkenes

Also known as olefins Aliphatic, unsaturated

• C=C double bonds Formula for one double bond = CnH2n

• subtract 2 H from alkane for each double bond Trigonal shape around C

• flat Polyunsaturated = many double bonds

Naming Alkenes and Alkynes

Change suffix on main name from -ane to -ene for base name of alkene, or to -yne for the base name of the alkyne

Number chain from end closest to multiple bond Number in front of main name indicates first

carbon of multiple bond

Alkenes

ethene = ethylene propene = propylene

produced by ripening fruit

used to make polyethylene used to make polypropylene74

Nomenclature of Alkenes

Find the longest carbon chain. Number the carbons such that the functional

group, here the double bond, gets the lowest possible number.

Substituents are cited before the parent longest chain, along with a number indicating its position at the chain.

2-buteneHigh electron density

Low electron density

Electrostatic map showshigh electron densityat double bond

5-methyl-3-heptene

6 5 43

2-methyl-3-hexene

H3CCH3

6 5 43

Name the Alkene

1. Find the longest, continuous C chain that contains the double bond and use it to determine the base name

Because the longest chain with the double bond has6 C the base name is hexene

2. Identify the substituent branches

Name the Alkene

there are 2 substituentsone is a 1 C chain, called methyl

the other one is a 2 C chain, called ethyl

b) then assign numbers to each substituent based on the number of the main chain C it is attached to

Name the Alkene

3. number the chain and substituents

a) determine the end closest to the double bond

• if double bond equidistant from both ends, number from end closest to the substituents

Name the Alkene

4. Write the name in the following ordera. substituent number of first alphabetical substituent –

substituent name of first alphabetical substituent – use prefixes to indicate multiple identical substituents

b. repeat for other substituentsc. number of first C in double bond – name of main chain

3–ethyl– 4–methyl– 2–hexene

Practice – Name the following

3,4-dimethyl-3-hexene

3 4 5 6

Physical Properties of Alkenes

Geometric Isomerism Because the rotation around a double bond is highly restricted,

you will have different molecules if groups have different spatial orientation about the double bond

This is often called cis–trans isomerism When groups on the doubly bonded carbons are cis, they are on

the same side of the double bond When groups on the doubly bonded carbons are trans, they are

on opposite sides

cis/trans Isomers

All substituents are on one side of bond

All substituents are on different sides

of bond

cis trans

Cis-Trans Isomerism

The cis and trans isomers are different molecules with different properties.

cis/trans Isomers

cis-2-pentene

cis/trans Isomers

7 trans-3-heptene

cis/trans IsomersThe main chain determines cis/trans in the name

cis-3-methyl-2-hexene

H3C CH31

6trans-3-methyl-2-hexene

This compound is cisbut the two methylgroups are … trans to each other.

This compound is transbut the two methylgroups are … cis to each other.

NOTE: For more than two substituents, the cis/trans system cannot be used

Reactions of Alkenes

Alkenes are relatively more reactive than alkanes.The electron-rich double bond is the ‘active site’ or the functional group of the molecule .

Organic Functional Groups

ClassFunctional Group

Example

Alkene C C

H3C CH2Limonene

Reactions of Alkenes

Addition ReactionsAn addition reaction is a reaction in which an unsaturated molecule becomes saturated by the addition of a molecule across a multiple bond.

Addition reaction to a double bond:

C C + X Y C C

Types of Addition Reactions

Note: For some alkenes, heat or light may be required.

1. Catalytic Hydrogenation: Alkenes and hydrogen react in the presence of a catalystto form alkanes.

C2H4 + H2 Ni C2H6

2(a) Addition of Halogen in inert solventHalogens dissolved in an inert solvent such as carbon tetrachloride, react readily with alkenes at room temperature and even in the dark.

CH3 CH CH2 + Br2 inert solvent CH3CHBrCH2Br propene bromine 1,2-dibromopropane

Addition Reactions

2(b) Addition of Halogen in waterChlorine or bromine dissolved water reacts with alkene to produce halohydrin as the major product.

CH3 CH CH2 + Br2 water CH3CH(OH)CH2Br + CH3CHBrCH2Br

propene bromine bromohydrin 1,2-dibromopropane (major product) (minor product)

Note: In both reactions 2(a) and 2(b), the red-brown colour of the bromine solution will disappeared.In reaction 2(b), bromine water contains HBr and HOBr.

Br2(aq) + H2O(l) ⇄ HBr(aq) + HOBr(aq)

Addition Reactions

3. Addition of Halogen halides

Addition reaction of alkenes with hydrogen halides (HX) form haloalkanes (alkyl halides) Relative reactivity of HX towards alkenes increases in the order of HF < HCl < HBr < HI

CH2 CH2 + HBr CH3CH2Br ethene hydrogen bromoethane

bromide

Reactions of AlkenesAddition of HBr to Alkenes

HBr(aq)

CH3 HBr(aq)H2C C

Predicting Major and Minor Addition Products:

The Markovnikov’s rule

When an HX molecule is added to an unsymmetrical alkene,the X atom attaches itself to the C atom (of the double bond)which is more alkylated (having less H atoms), while the H atombonds to the adjacent C atom with larger number of H atoms (already bonded to it).

When an HX molecule is added to an unsymmetrical alkene, two possible products can be formed:

CH3CH CH2 + HBr CH3CHBrCH3 + CH3CH2CH2Br

propene 2-bromopropane 1-bromopropane

(major product) (minor product)

Electrophile and Nucleophile

An electrophile is a species (ion or molecule) which attacks electron-rich site of organic molecules such as double bonds.Electrophiles are Lewis acids (either positive ions or molecules with electron-deficient atom) Examples: HCl , H3O+

A nucleophile is a species (ion or molecule) which attacks electron-poor carbon atom of organic molecule, by donating electron-pair to the atom.Nucleophiles are Lewis bases, containing lone pair of electronsExamples: CH3NH2 H2OHO Cl

Reaction Mechanism: Electrophilic Addition

Hydrogen bromide is a strong acid and formshydronium ions, H3O+, and bromide, Br–, when dissolved in water.

electrophile

HBr + H2O Br + H3O

H3O+ is positively charged, thus it is electron deficient. It is electrophilic (electron-loving)

Reaction mechanism: Electrophilic attack

The hydronium ion reacts with the C=C bond,producing an electrophilic carbocation

Carbocation

H3CCH2C

+ + H2O

Note: Another carbocation CH3CH2CH(CH3)C⁺H2 is also formed, but it is less stable.

Reaction mechanism:

Br– is rich in electrons. It is nucleophilic. Br– seeks for the electron-poor carbocation. The two species, electrophile and nucleophile, combineand form a new compound, 2-bromo-2-methylpropane

+ Br H2C

Note: Reaction of Br– with the other carbocation CH3CH2CH(CH3)C⁺H2 will produce the minor product, 1-bromo-2-methylpropane. This is the minor product as predicted by the Markovnikov’s rule.

2-bromo-2-methylpropane (Major product)

Electrophilic Addition: Summary of Mechanism

Step 1 reaches a carbocation “intermediate.” One new bond is formed.

Step 2 completes the reaction by forming a secondbond. Again, it is the interplay between positively charged (electrophilic) and negatively charged (nucleophilic) species.

Overall Mechanism of Electrophilic Addition

Summarizing our reaction, we realize it is a 2-step mechanism

HBr + H2O Br + H3O

STEP 1

STEP 2

H3CCH2C

+ + H2O

+ Br H2C

Addition Reactions

4. Addition with acidified water (H3O+) : Hydration of alkenes

Addition of H and OH groups from a water molecule to a double bond will produce an alcohol. The reaction is facilitated by using an acid as a catalyst.

CH3CH CH2 + H2O H2SO4 CH3CH(OH)CH3

2-propanol

Hydration of alkenes using concentrated H2SO4 followed by hydrolysis, would give the same results.

Unsaturation Tests for Alkenes

Alkenes or unsaturated organic compounds may be identified using simple lab tests

1. Br2 in inert solvent or dilute bromine water are yellow brown in colour. The solution is decolorised when added to an alkene (See: Addition reactions with halogens)

2. Reaction with cold, dilute, alkaline KMnO4 (Baeyer’s test)Alkenes are oxidised readily by the Baeyer’s reagent. The purple colour of the KMnO4 solution disappears, and a brown precipitate of Mn(IV) oxide appears. The organic product is a diol. CH3(CH2)6CHCH2 KMnO4 (aq), OH⁻ CH3(CH2)6CH(OH)CH2OH

1-nonene a diol

Unsaturation Tests for Alkenes

3. Reaction of Alkenes with hot, acidified KMnO4

Vigorous oxidation of alkenes results in the cleavage ofthe double bonds producing ketones, carboxylic acids or CO2

CH3CH CHCH2 CH3 KMnO4/H+

CH3COOH + CH3CH2COOH

carboxylic acids

In this reaction, the KMnO4 solution is decolourised. By identifying the products, the position of the double bond in the alkene can be determined.

Alkynes

Aliphatic, unsaturated CC triple bond Formula for one triple bond = CnH2n−2

• subtract 4 H from alkane for each triple bond

Linear shape Internal alkynes have both triple bond carbons

attached to C Terminal alkynes have one carbon attached to H

Alkynes

both used in welding torches

Name the Alkyne

1. Find the longest, continuous C chain that contains the triple bond and use it to determine the base name

Because the longest chain with the triple bond has 7 C the base name is heptyne

2. Identify the substituent branches

Name the Alkyne

there are 2 substituentsone is a 1 C chain, called methylthe other one is called isopropyl

Name the Alkyne

1234567

3. number the chain and substituents

a. determine the end closest to the triple bond if triple bond equidistant from both ends, number from

end closest to the substituents

b. then assign numbers to each substituent based on the number of the main chain C it is attached to.

Name the Alkyne

4. write the name in the following ordera) substituent number of first alphabetical substituent –

substituent name of first alphabetical substituent – use prefixes to indicate multiple identical substituents

b) repeat for other substituentsc) number of first C in triple bond – name of main chain

4–isopropyl–6–methyl–2–heptyne

1234567

Practice – Name the Following

3,3-dimethyl-1-pentyne

Examples of Naming Alkynes

Examples of Naming Alkenes

Alkyne Reactions:

Hydrogenation = adding H2

• alkene or alkyne + H2 → alkane

• generally requires a catalyst

Halogenation = adding X2

Hydrohalogenation = adding HX• HX is polar

• when adding a polar reagent to a double or triple bond, the positive part attaches to the carbon with the most H’s

Alkynes undergo many reactions similar to alkenes:

Alkynes: Reactions

C CH3C CH3

Alkynes are electron-rich molecules, thus also electrophilic addition takes place.

2-butyne vinyl-carbocation

Alkynes: Reactions

After the addition of the nucleophile we obtain an alkenethat still can be attacked by an electrophile.

Alkynes: Reactions

CH3 HBr

Formation of a second carbocation

Alkynes: Reactions

Both nucleophiles end up on the same carbon.

Aromatic Compounds

An aromatic compound is a compound that contains a benzene ring in its molecule.Aromatic hydrocarbons are also called arenes

The Structure of benzene (C6H6)

Derivatives of benzene: Other compounds have the benzene ring with other groups substituted for some of the Hydrogens

Aromatic Hydrocarbons

Aromatic hydrocarbons contain a ring structure that seems to have C=C, but doesn’t behave that way

The most prevalent example is benzene.• C6H6

• Other compounds have the benzene ring with other groups substituted for some of the Hydrogens

Naming Monosubstituted Benzene Derivatives

halogen substituent

Names of a common derivatives

Naming Benzene as a Substituent

When the benzene ring is not the base name, it is called a phenyl group

Naming Disubstituted Benzene Derivatives

Number the ring starting at attachment for first substituent, then move toward second

• order substituents alphabetically

• use “di” if both substituents are the same

Practice – Name the Following

1-chloro-4-fluorobenzene 1,3-dibromobenzeneor meta-dibromobenzene

or m-dibromobenzene

Polycyclic Aromatic Hydrocarbons

Contain multiple benzene rings fused together

• fusing = sharing a common bond

Alcohols

Aliphatic, hydroxy compounds• Contain hydroxy functional groups (—OH)

General formula = CnH2n + 1OH (n ≥ 1)

Considered as derivatives of alkanes with H atoms replacedby OH groups.

R—H R—OHalkane alcohol

Functional Groups Other organic compounds are hydrocarbons in which

functional groups have been substituted for hydrogens A functional group is a group of atoms that show a

characteristic influence on the properties of the molecule• generally, the reactions that a compound will perform are

determined by what functional groups it has

• because the kind of hydrocarbon chain is irrelevant to the reactions, it may be indicated by the general symbol R

CH3—OH

R group functional group

Alcohols R—OH Ethanol = CH3CH2OH

• grain alcohol = fermentation of sugars in grains

• alcoholic beverages• proof number = 2x percentage of alcohol

• gasohol Isopropyl alcohol = (CH3)2CHOH

• 2-propanol• rubbing alcohol• poisonous

Methanol = CH3OH• wood alcohol = thermolysis of wood• paint solvent• poisonous

Naming Alcohols

Identify main chain containing OH group Number main chain C atoms from end closest to

the OH group Give base name ol ending and place number of C

on chain where OH is attached in front Name all substituents present and write the lowest

possible numbers List substituents in alphabetical order

Naming Alcohols

CH3CH2CH2CH2CHCH2OH

CH2CH2CH3C

Give the IUPAC name of the alcohol:

Naming Alcohols

CH3CH2CH2CH2CHCH2OH

CH2CH2CH3

1 2 3 4 5

1 2 3 4 5 6

Determine longest chain with OHBlue chain is longer; however,Red chain contains OH

Naming Alcohols

CH3CH2CH2CH2CHCH2OH

CH2CH2CH3

123456

Determine longest chain with OHBlue chain is longer; however,Red chain contains OH

Name: 2-propyl-1-hexanol

Notice that numbering starts at alcohol group

Classification of alcohols

Based on the number of alkyl groups (R) bonded to the C atom that carries the -OH group, alcohols are classified into three types:

Primary, Secondary, and Tertiary

CH2 OHR CH OHR

R'C OHR

R10 20 30

Reactions of Alcohols

Nucleophilic substitution: 1. Reaction with H ─X

CH3─OH + HCl CH3Cl + H2O

2. Reaction with PCl3

CH3─ CH2OH CH3─ CH2ClPCl3

Cl⁻ acts as a nucleophile, replacing –OH group

Note: Conversion of an alcohol to a haloalkane can also be done by using PCl5 or SOCl2 (thionyl chloride) instead of PCl3

I + H2O

cyclohexanol iodocyclohexane

Cl + H2O

1-propanol 1-chloropropane

**Substitution reactions may be used to convert an alcohol to a haloalkane

Elimination Reaction (Dehydration)

Elimination of water, dehydration, is commonly obtained using sulfuric acid (H2SO4) as a catalyst.

OH H2SO4

H3CHC CHCH3 + H2O

**Dehydration can be used to convert alcohols to alkenes

Elimination (Dehydration)

The ease of dehydration follows the order:

Elimination reaction

OH 1-pentene (minor product)

2-pentanol

2-pentene (major product)

Saytzeff’s rule: For elimination reaction that produces more than one alkenes, the alkene with more than one alkyl substituents in the double bond is the predominant product.

Reactions of Alcohols

3. Oxidation: Dehydrogenation

CH3CH2OH CH3CHO CH3COOH −2 H −2 H

Typical oxidizing agents are:

1. Acidified potassium dichromate (K2Cr2O7) or chromic acid H2CrO4

2. Acidified potassium permanganate (KMnO4)

Oxidation of Alcohols

Remember, we distinguish three types of alcohols:

aldehyde

R'ketone

Dehydrogenation (oxidation) is possible for 10 and 20 leading to aldehydes and ketones, respectively. 30 resists oxidation

CH2 OHR CH OHR

R'C OHR

R10 20 30

10 alc. 20 alc.

Oxidation of Alcohols

Aldehydes can be further oxidized to carboxylic acids.

aldehyde acid

Oxidation of alcohols

H2CrO4

cyclopentanol cyclopentanone

OHH2CrO4 O

H2CrO4

butanolbutanal

butanoic acid

Reaction of alcohols with very active metals

2 CH3─OH + 2 K 2 CH3O−K+ + H2 potassium methoxide

2 CH3CH2─OH + 2 Na 2 CH3CH2O−Na+ + H2 sodium ethoxide

Tests to Distinguish Classes of Alcohols

Two simple lab tests can be used to distinguish between Primary, secondary and tertiary alcohols:

1. Lucas test: The alcohols is shaken with a solution of ZnCl2 in concentrated HCl. (Lucas reagent)

For a 30 alcohol , the solution turns cloudy almost immediately.

For a 20 alcohol , cloudiness* observed in about 5 minutes.

10 alcohol shows no cloudiness.*Cloudiness is due to the formation of alkyl halide

Lucas Reagent Test

OH Cl ZnCl2 / HCl

2-2-butanol 2-chloro-2-methylbutane

(a 30 alcohol) (Cloudiness appears immediately)

ZnCl2 / HCl

OH Cl 2-pentanol 2-chloropentane (a 20 alcohol) (cloudiness appears in a few minutes)

No reaction

OH propanol (a 10 alcohol)

2. Oxidation test:

Only 10 and 20 alcohols are oxidised by hot acidified KMnO4 or hot acidified K2Cr2O7 solution.

10 and 20 alcohols decolourise the KMnO4 solution, whereas the colour of the K2Cr2O7 solution changes from orange to green.

No reaction for 30 alcohols.

3. Iodoform test

Ethanol and 20 alcohols with methyl alcohol group

CH3C (methyl alcohol group)

OHreacts with iodine in aqueous NaOH to produce pale yellowsolid of iodoform (CHI3).

CH3CH2OH I2 / NaOH CHI3

Triiodomethane (iodoform) yellow precipitate

Haloalkanes Also called alkyl halides General formula = CnH2n + 1X (n ≥ 1), or R‒ X

X = F, Cl, Br or I Functional Group:

‒ C ‒ X

Nomenclature

Name as derivative of alkane:

replacing the H atom(s) by halogen atom(s)

Positions of halogen atoms are indicated by thenumber assigned to the C atom to which it is attached

CH3CH2Br (CH3)3CI IUPAC name: bromoethane 2-iodo-2-methylpropaneCommon name: ethyl bromide tert-butyl iodide

Nomenclature

Name the compounds:

a) CH3CH2CH (CH3)CH2CHCH3

2-chloro-4-methylhexane

b) Br CH3

1-bromo-3-methylcyclopentane

Reactions of Haloalkanes

The C — X bonds in haloalkanes are polar bonds

The C atom is electron-poor, it attracts nucleophiles δ+ δ-

— C — X

Reactions of haloalkanes include:

1. Elimination2. Nucleophilic substitution3. Grignard reactions

Reactions of haloalkanes

Elimination Reaction: Dehydrohalogenation adjecent H and X atoms are removed to produce a

double bond (an alkene)

R—CH —CH2 R—CH CH2 + HX

H X alkene

Example: When bromoethane is heated with a solution of NaOH in ethanol under reflux, elimination of HBr occurs and ethene is produced.

H—CH —CH2 Ethanolic NaOH H—CH CH2 + HBr

H Br ethene

Reactions of haloalkanes

Dehydrohalogenation of alkyl halides follows the Saytzeff’s rule. When more than one alkenes can be formed, the alkene with double bond containing more alkyl substituents is the predominant product.

Example: Dehydrohalogenation of 2-iodobutane by refluxing with alcoholic KOH produces:

2-butene

H H H CH3CH CH—CH3 (major product)

CH3C—C—CH

H I H CH3CH2CH CH2 (minor product)

2-iodobutane 1-butene

Nucleophilic Substitution Reactions

The reaction of alkyl halides with hydroxide ion in aqueous solution is a nucleophilic substitution reaction. The OH− acts as a nucleophile, relpacing the halogen atom to form an alcohol

CH3 — C — Cl + OH − heat CH3 — C — OH

Chloroethane ethanol

Grignard Reactions

When an alkyl halide reacts with a metal such as Mg, an organometallic compound, called the grignard reagent , is produced.

R — X + Mg ether R — Mg — X

a Grignard reagent

The reaction must be carried out in the absence of water. Diethyl ether is often used as the solvent.

The Grignard reagent is a very strong Lewis base. The alkyl portion of the molecule can act as a nucleophile. It reacts rapidly with molecules having acidic H atom including water, producing an alkane.

δ‒ δ+

CH3CH2— Mg—Br + H — OH CH3CH3 + BrMgOH

ethylmagnesium bromide water ethane

Grignard reagent is primarily used in the synthesis of alcohols. It reacts with aldehyde or ketone to produce alcohols of the desired structures. (See: Reactions of Aldehyde and Ketone)

Aldehydes and Ketones Contain the carbonyl group Aldehydes = at least 1 side H Ketones = both sides R groups Many aldehydes and ketones have

pleasant tastes and aromas Formaldehyde : H2C=O

• pungent gas• formalin = a preservative• wood smoke, carcinogenic

Acetone : CH3C(=O)CH3

• nail-polish remover

Aldehyde Odors and Flavors

butanal = butter

vanillin = vanilla

benzaldehyde = almonds

cinnamaldehyde = cinnamon

acetophenone = pistachio

carvone = spearmint

ionone = raspberries

muscone = musk

Ketone Odors and Flavors

Naming Aldehydes and Ketones Main chain contains C=O group Number the main chain from end closest to C=O For aldehydes, give base name al ending

• always on C1

For ketones, give base name one ending and according to number of C on chain where C=O attached

Reactions of Aldehydes and Ketones

The carbonyl group in aldehydes and ketones has a constant polarity.

C=O δ+ δ−

The O atom attracts electrophiles; the C atom attracts nucleophiles

Addition of HCN to C=O

polar molecule HCN adds across the C=O, with the positive part (H) attaching to O; the nucleophile CN attaching to C atom

2-hydroxypropanenitrile

Reduction Reactions of Aldehydes and Ketones

Aldehydes and ketones are generally synthesized by the oxidation of alcohols

Therefore, reduction of an aldehyde or ketone results in an alcohol.

Common reducing agents are H2 with a Ni catalyst, NaBH4, and LiAlH4

Catalytic hydrogenation reactions:

RCHO H2/Ni or LiAlH4 RCH2OH (a 10 alcohol)

R —C — R’ H2/Ni or LiAlH4 R — C — R’ (a 20 alcohol)

Oxidation of Aldehydes

Aldehydes are easily oxidised using mild oxidising agents Ketones would not oxidise even using strong oxidising agents

A. Tollen’s reagent (Silver mirror test)

Tollen’s reagent is a solution of silver nitrate in ammonium hydroxide containing the silver complex Ag(NH3)2

An aldehyde is oxidised by Ag(NH3)2 + , which is reduced to

metallic Ag. Ketones give no reaction.

RCHO + 2Ag(NH3)2+ + OH‒ RCOO‒ + 2Ag + 2NH4

+ + 2NH3

Oxidation of Aldehydes

B. Fehling’s reagent test for aldehydes

Fehling’s reagent consists of a basic solution of Cu(II) complex with a deep blue colour.

It oxidises aldehyde, and is itself reduced to a brick-red deposit of Cu(I) oxide. Ketones give no reaction.

RCHO + 2Cu2+(complex) + 5OH‒ RCOO‒ + Cu2O + 3H2O

*Aldehydes also decolourise acidified solution of KMnO4

C. Iodoform test for ethanal, CH3CHO, and methyl Ketones

A methyl ketone has a CH3 group attached to the carbonyl carbon. O

R — C — CH3 R = H or any alkyl group

The reagent consists of an aqueous solution of I2 in NaOH or KOH. On reacting with ethanal, a yellow precipitate of triiodomethane (iodoform) appears.

CH3CHO + 3 I2 + NaOH CH3COONa + CH3I + 3HI

Note: ethanol, CH3CH2OH or a sec. alcohol with the group CH3CH —

also give positive iodoform tests. OH

Reactions of Aldehydes and Ketones

Reaction of Grignard Reagents (RMgX)

a) With methanal gives a 10 alcohol

RMgX + HCHO ether R— CH2OMgX H2O/H+ RCH2OH (a 10 alcohol)

b) With other aldehydes give 20 alcohol

RMgX + R′CHO ether R′— CHOMgX H2O/H+ R′— CHOH

(a 20 alcohol)

With ketones gives 30 alcohol

O OMgX OH

RMgX + R′ — C — R″ ether R′—C—R″ H2O/H+ R′—C—R″

(a 30 alcohol)

Carboxylic Acids

• CnH2n + 1COOH (n ≥ 0)

• RCOOH

• Sour tasting

• Weak acids• Citric acid

found in citrus fruit

• Ethanoic acid = acetic acid, CH3COOH vinegar

• Methanoic acid = formic acid, HCOOH insect bites and stings

Synthesis of Carboxylic Acids

Made by the oxidation of aldehydes and alcohols

Naming Carboxylic Acids

Carboxylic acid group always on end of main chain

• has highest naming precedence of functional groups C of group always C1

• position not indicated in name Change ending to oic acid

Examples of Naming Carboxylic Acids

Practice – Name the following

hexanoic acid(aka caproic acid, which causes

foot odor)

2-hydroxy-3-methylbutanoic acid

Reactions of Carboxylic Acids

Neutralisation: Reactions with bases to form salts of the acids and water. RCOOH + NaOH RCOONa + H2O

Reactions with Reactive Metals : forming salts of the acids and H2 gas

2CH3COOH + 2Na 2CH3COONa + H2

Reactions with hydroegn carbonates: forming salts of the acids, CO2 and H2O

RCOOH + NaHCO3 RCOONa + CO2 + H2O

Reductions of Carboxylic Acids

Carboxylic acids are reduced by very strong reducing agents such as lithium aluminum hydride in ether, producing primary alcohols.

RCOOH LiAlH4/ether RCH2OH + H2O

Esterification

When a carboxylic acid is heated with an alcohol in the presence of concentrated sulphuric acid as catalyst, an ester is produced.

RCOOH + R′OH conc. H2SO4 RCOOR′ + H2O

Example:

CH3CH2COOH + CH3OH conc. H2SO4 CH3CH2COOCH3 + H2O propanoic acid methanol methylpropanoate

Esters R–COO–R′ Sweet odor Made by reacting carboxylic acid with an alcohol in the

presence of conc. sulphuric acid as catalyst

RCOOH + R′OH conc. H2SO4 RCOOR′ + H2O

Naming Esters

Carboxylic acid group always on end of main chain

• unless carboxylic acid group present C of ester group on C1

• position not indicated in name Begin name with alkyl group attached to O Name main chain with oate ending

Hydrolysis of Esters

Hydrolysis of esters is the reverse of esterification Acid Hydrolysis of an ester in the presence of dilute HCl or dilute

sulphuric acid produces an alcohol and a carboxylic acid If an alkali is used instead of an acid, the carboxylic acid formed will

be converted to the salt

CH3CH2COOCH3 + H2O H+/reflux CH3CH2COOH + CH3OH

methylpropanoate propanoic acid methanol

CH3CH2COOCH3 + NaOH reflux CH3CH2COONa + CH3OH

methylpropanoate sodium propanoate methanol

Ch5 Organic Chemistry

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