Alkenes and Alkynes• Contain C-C double and triple bonds• General alkene formula Cn H2n

• General alkyne formula Cn H2n-2

• More reactive than alkanes• Known as unsaturated hydrocarbons

CC HHH H

Thermal cracking:Process of breaking the long chain-alkanes found in petroleum into shorter chain alkanes and alkenes.

• Multiple bonds are also formed by removing ahydrogen chemically – dehydrogenation.

C C H

H

H + H2

H

H H

C C HH

H H

C C H

H

H + H2

H

C C HH

Alkenes / Alkynes are converted to alkanes byhydrogenation or addition reaction.

• Find parent chain with the double/triple bond.• Named as total carbons using ending ene / yne

• Show the location of the bond by the carbon number separated with a hyphen. (2-pentene)

• Number carbons from the end that gives the lowest

number to the double or triple bond.

• Name alkyl branches as in alkanes.

Naming Alkenes and Alkynes

ethene CH2= CH2

C = C H

HH

H

ethyne CH ≡ CH

C ≡ C HH

CC HHH H

CC HH

2-hexene CH3CH=CHCH2CH2CH3

3-hexyne CH3CH2C≡CCH2CH3

C - C - C - CC - C = 654321

C ≡ C - C - CC - C - 654321

4-methyl-2-pentene

(4-methylpent-2-ene)

(Note, lowest number goes to the double bond)

CH3CH2CH(CH3)CH=C(C2H5)CH2CH3

3-ethyl-5-methyl-3-heptene

1234567

*Show double/triple bond in condensed formula.

Draw the structural formula for 1-butene.

CH2=CH–CH2–CH3

Draw a condensed for 2,5,5-trimethyl-2-hexene.

CH3C(CH3)=CHCH2C(CH3)2CH34321 5 6

HC≡CCH2C(C2H5)2CH2CH(CH3)CH(CH3)CH3

4,4-diethyl-6,7-dimethyl-1-octyne

1 2 3 4 5 6 7 8

Draw a structural of 2,2,5,5-tetramethyl-3-hexyne.

• Like Alkyl groups (trimethyl), prefixes and numbers must be used to indicate multiple double or triple bonds.

C = C – C = C 1,3-butadiene

3-methyl-1,4-pentadiyne

4321

4321 5

C ≡ C – C – C ≡ C

C

• Alkenes: C=C, CnH2n , –ene.

• Alkynes: C≡C, CnH2n-2 ,–yne.

• Parent chain is numbered to give the double or triple bond the lowest number.

• Draw the parent chain hydrocarbon with the double or triple bonds first.

• Add in alkyl groups and then hydrogen so eachcarbon has 4 bonds.