Organic Chemistry

6. If both directions lead to the same number for the alkene functional group suffix
   and the same low number(s) for one or more of the substituents, then those sub-
   stituents are ignored and the direction is chosen that gives the lowest number to
   one of the remaining substituents.

The carbons of an alkene are called vinylic carbons. An carbon that is ad-

jacent to a vinylic carbon is called an allylic carbon.

Two groups containing a carbon–carbon double bond are used in common names—

the vinyl groupand the allyl group. The vinyl group is the smallest possible group

that contains a vinylic carbon; the allyl group is the smallest possible group that con-

tains an allylic carbon. When “allyl”is used in nomenclature, the substituent must be

attached to the allylic carbon.

PROBLEM 4

Draw the structure for each of the following compounds:

a. 3,3-dimethylcyclopentene c. ethyl vinyl ether

b. 6-bromo-2,3-dimethyl-2-hexene d. allyl alcohol

PROBLEM 5

Give the systematic name for each of the following compounds:

a. d.

b. e.

c. Br f. CH 3 CH CHOCH 2 CH 2 CH 2 CH 3

CH 3 CH 2 C CCHCH 3 CH 3 CH 3

CH 3

CH 3

Cl

BrCH 2 CH 2 CH CCH 3

CH 2 CH 3

CH 3 CHCH CHCH 3

CH 3

H 2 C CH CHCH 2

CHCH 2 Br

the vinyl group

H 2 C CHCl

chloroethene

vinyl chloride

H 2 C

3-bromopropene

allyl bromide

systematic name:

common name:

H 2 C

the allyl group

RCH 2 CH CH CH 2 R

vinylic carbons

allylic carbons

sp^2 sp^3

CH 3 CHCH 2 CH CCH 2 CHCH 3

2-bromo-4-ethyl-7-methyl-4-octene

not

7-bromo-5-ethyl-2-methyl-4-octene

because 4 < 5

CH 3 CH 2 CH 3

Br

6-bromo-3-chloro-4-methylcyclohexene

not

3-bromo-6-chloro-5-methylcyclohexene

because 4 < 5

Br

Cl

CH 3

Section 3.2 Nomenclature of Alkenes 115

Tutorial:

Common names of alkyl

groups

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