CHE 102 Chap 191

Chapter 20

Unsaturated Hydrocarbons

CHE 102 Chap 192

Unsaturated Hydrocarbons

• Alkenes (C=C) • Alkynes ( )• Aromatic

C C

CHE 102 Chap 193

sp2 Hybridization (C=C)

CHE 102 Chap 194

CHE 102 Chap 195

sp – Hybridization ( )C C

CHE 102 Chap 196

IUPAC Rules for Naming Alkenes

• Select the longest continuous carbon-carbon chain that contains the double bond.

• Name this parent compound as you would an alkane but change the –ane ending to -ene; for example, propane is changed to propene.

CH3CH2CH3propane

CH2CHCH3propene

CHE 102 Chap 197

IUPAC Rules Continued

• Number the carbon chain of the parent compound starting with the end nearer to the double bond. Use the smaller of the two numbers to indicate the position of the double bond. Place this number in front of the alkene name; for example, 2-butene means that the carbon-carbon double bond is between carbons 2 and 3.

CHE 102 Chap 198

IUPAC Rules Continued

• Branch chains and other groups are treated as in naming alkanes, by numbering and assigning them to the carbon atom to which they are bonded.

CHE 102 Chap 199

Two or more C=C double bonds

CH2CHCHH2C

1,3-butadiene

Fourcarbon atoms

InsertedTo ease

pronunciation

TwoDoublebonds

Positionof thedoublebonds

CHE 102 Chap 1910

Cycloalkenes

• Just like normal cycloalkanes except the numbering always starts at the double bond.

CH

CHCH2

H2C

H2CCH2

cyclohexene

Cl

1

2

3

4

5

6

3-chlorocyclohexene

CHE 102 Chap 1911

Geometric Isomers (Cis/Trans)

• Structural Isomers– Same formula

– Different structure

• Geometric Isomers– Same formula

– Same structure

– Different geometry

CHE 102 Chap 1912

No geometric isomers for C-C

CC H

Cl

H

H

Cl

H

CC H

H

Cl

H

Cl

H

“free rotation”

CHE 102 Chap 1913

Different Properties = Different Molecules

Cis-1,2-dichloroethene

CCCl Cl

HH

trans-1,2-dichloroethene

CCH Cl

HCl

(bp=60.1°C) (bp= 48.4°C)

CHE 102 Chap 1914

Cis vs Trans

CC

aa

b b

cis isomer

CCba

b a

trans isomer

CHE 102 Chap 1915

CCH

H

H

H

Two groupsthe same

CCCH3

H

H

H

• cis and trans cannot be used if 2 of the same groups are on one side of the double bond.

– These do not have isomerism

CHE 102 Chap 1916

Isomers of C5H10

CHE 102 Chap 1917

C C

Chain

H

Chain

H

C C

Chain

H Chain

H

Cis/Trans Isomers in Biology

CHE 102 Chap 1918

Reactions of Alkenes

• Alcohols– Dehydration/Hydration

• Oxidation

• Addition– Hydrogenation

– Halogenation x2

– Hydration

– Markovnikov’s Rule

CHE 102 Chap 1919

Alkenes and Alcohols

CC CH3

H

OH

CH3

H

H

conc. H2SO4 CC CH3

H

CH3

H

+ H2O

Dehydration

Hydration

CH2 CH2 + HOH H+

CH3CH2OH Ethanol

CHE 102 Chap 1920

Oxidation

ethene

CH2H2C + KMnO4 + H2O

ethylene glycol

CH2H2C

OHOH

+ MnO2 + KOH

Purple Brown

“Bayer Test for C=C”

CHE 102 Chap 1921

Hydrogenation (Addition)

CH2 + H2 CH2Pt, 250 C

1 atmCH3CH3

CHE 102 Chap 1922

Halogenation (Addition)

+ CH2H2C BrBr CH2Br CH2BrReddish-Orange Clear

CHE 102 Chap 1923

Addition Reactions

+ HCl CH2H2C CH3CH2Cl

CHE 102 Chap 1924

Dilemma

CH3 CH CH2 + HCl

CH3CHClCH3

CH3 CH2 CH2ClX

(about 100 %)

(trace)

CHE 102 Chap 1925

Carbocations

C+

H

H

H

MethylCarbocation

C+

H

H

CH3

EthylCarbocation (primary)

C CH3CH3

H

+

IsopropylCarbocation(secondary)

C

CH3

CH3

CH3

+

t-ButylCarbocation (tertiary)

Stability of carbocations: 3o > 2 o > 1o > CH 3+

CHE 102 Chap 1926

Markovnikov’s Rule

When an unsymmetrical molecule such as HX(HCl)adds to a carbon-carbon double bond, the hydrogen from HX goes to the carbon atom that has the greaternumber of hydrogen atoms.

CHE 102 Chap 1927

C CH2

CH3

CH3 + HI C

CH3

CH3CH3

I

CHE 102 Chap 1928

Alkynes• IUPAC Rules for Naming• ane yne• Use # to indicate position of triple bond• Reactions:

– Combustion

– Halogenation

– Addition

• Properties– Low Bp/Mp (Lower Mass)

– Non-polar

– Very reactive

CHE 102 Chap 1929

Aromatic Structure

CHCH

CHCH

HC

HCCH

HC

HCCH

CH

CH

CHE 102 Chap 1930

Naming

• Sidechains:

CH

CH3

CHClCH2CH3

3-Chloro-2-phenylpentane

CH2

diphenylmethane

CHE 102 Chap 1931

Special Aromatics

Nitrobenzene

O2N

CH3

TolueneMethylbenzene

OH

PhenolHydroxybenzene

C OOH

Benzoic acid

C OH

Benzaldehyde

NH2

Aniline

(aminobenzene)

CHE 102 Chap 1932

Disubstituted

G

orthoortho

meta meta

para

CHE 102 Chap 1933

Examples

Cl

Cl

Ortho-dichlorobenzene1,2-dichlorobenzene

Cl

Cl

meta-dichlorobenzene1,3-dichlorobenzene

Cl

Cl

para-dichlorobenzene1,4-dichlorobenzene

Cl

Br

o-bromochlorobenzene

NO2

CH2CH3

m-ethylnitrobenzene

CHE 102 Chap 1934

Special CasesCH3

CH3

o-xylene

CH3

CH3

m-xylene

CH3

CH3

p-xylene

OH

NO2

o-nitrophenol

NH2

Br

p-bromoaniline

CH3

NO2

m-nitrotoluene

o-xylenep-xylenem-xylene

CHE 102 Chap 1935

Poly Substituted

• # ring to give lowest overall numbers• Special groups always labeled #1

NO2

NO2NO2

1,3,5-trinitrobenzene

1

2

3

4

5

6

Br

Br

Br

1,2,4-tribromobenzene

12

3

4

5

6

CH3

NO2

NO2

NO2

2,4,6-trinitrotoluene(TNT)

12

3

4

5

6 Br OH

Cl

5,bromo-2-chlorophenol

1

2

3

4

56

CHE 102 Chap 1936

Reactions

• Halogenation• Nitration• Alkyl substitution• Side chain oxidation

CHE 102 Chap 1937

Halogenation

+ X2 FeX3

Benzene Chlorine orBromine

X+ HX

Chlorobenzene orBromobenzene

CHE 102 Chap 1938

Nitration

+ HO NO2 H2SO4

Nitric acid

NO2+ H2O

nitrobenzene

CHE 102 Chap 1939

Alkyl Substitution

+ CH3CH2Cl AlCl3

benzene chloroethane

CH2CH3+ HCl

ethylbenzene

CHE 102 Chap 1940

Side Chain Oxidation

CH3 O COOH

Benzoic Acid

CH2CH3O COOH

+ CO2

CHE 102 Chap 1941

Alkynes

C C