Organic Chemistry

OH NH 2 CC CC

the double bond is given priority over

a triple bond only when there is a tie

>>>=

increasing priority

CO

Table 8.1 Priorities of Functional Group Suffixes

300 CHAPTER 8 Reactions of Dienes • Ultraviolet and Visible Spectroscopy

If there is a tie between a double bond
and a triple bond, the double bond gets
the lower number.

A chain is numbered to give the lowest
possible number to the functional group
with the highest priority.

If the same low number is obtained in both directions, the chain is numbered in the di-

rection that gives the double bond the lower number.

The relative priorities of the functional group suffixes are shown in Table 8.1. If the

second functional group suffix has a higher priority than the alkene, the chain is num-

bered in the direction that assigns the lowest possible number to the functional group

with the higher priority.

CH 3

OH

6-methyl-2-cyclohexenol

NH 2

3-cyclohexenamine

CH 3 C CHCH 2 CH 2 OH

4-methyl-3-penten-1-ol

CH 2 CHCH 2 OH

2-propen-1-ol

not 1-propen-3-ol

CH 3 NH 2

CH 2 CHCH 2 CH 2 CH 2 CHCH 3

6-hepten-2-amine

CH 3 CH CHC CCH 3

1 2 3 4 56

2-hexen-4-yne

not 4-hexen-2-yne

HC CCH 2 CH 2 CH CH 2

6 54 3 21

1-hexen-5-yne

not 5-hexen-1-yne

CH 3 CH CHCH 2 CH 2 C CH

7 6 5 4 3 2 1

5-hepten-1-yne

not 2-hepten-6-yne

because 1 < 2

CH 2 CHCH 2 CH 2 C CCH 3

1 273 4 5 6

1-hepten-5-yne

not 6-hepten-2-yne

because 1 < 2

CH 2 CCH 3

CH 2 CH 2 CH 2 CH 3

CHCHC

123456

3-butyl-1-hexen-4-yne

the longest continuous chain has eight carbons, but the 8-carbon

chain does not contain both functional groups; therefore, the

compound is named as a hexenyne because the longest continuous

chain containing both functional groups has six carbons

HOW A BANANA SLUG KNOWS WHAT TO EAT

Many species of mushrooms synthesize 1-octen-3-ol, which serves as a repel-

lent that drives off predatory slugs. Such mushrooms can be recognized by

small bite marks on their caps, where the slug started to nibble before the volatile compound

was released. Humans are not put off by the smell because, to them, 1-octen-3-ol smells like

a mushroom. 1-Octen-3-ol also has antibacterial properties that may protect the mushroom

from organisms that attempt to invade the wound made by the slug. Not surprisingly, the

species of mushroom that banana slugs commonly eat cannot synthesize 1-octen-3-ol.

When the functional groups are a
double bond and a triple bond, the
chain is numbered to get the lowest
possible number in the name of the
compound, regardless of which
functional group gets the lower number.

CH 3 CH 2 CH 2 CH 2 CH 2 CHCH CH 2

OH

1-octen-3-ol