The Foundations of Chemistry

Solution

Then we fill in enough hydrogens to saturate each C atom and arrive at the structure

EXAMPLE 27-5 Writing Formulas from Names

Write the structure for the compound 2-cyclopropyl-3-ethylpentane.

Plan

The root name “pentane” tells us that the structure is based on a five-carbon chain. We place

the substituents at the positions indicated by the numbers in the name.

Solution

You should now work Exercise 16.

The names of substituted cycloalkanes are derived analogously to those of alkanes.

(1) The base name is determined by the number of carbon atoms in the ring using the

same base name as the alkane with the addition of cyclo in front. (2) If only one substituent

is attached to the ring, no “location number” is required because all positions in a

cycloalkane are equivalent. (3) Two or more functional groups on the ring are identified

by location numbers, which should be assigned sequentially to the ring carbons in the

order that gives the smallest sumof location numbers.

CH 3

CH 2 CH 3

CH 3

CH 3

CH 3

1

2

4 3

5

1,3-dimethylcyclopentane

(not 1,4-dimethylcyclopentane)

methylcyclobutane 1-ethyl-1-methylcyclopropane

CH 3 CH CH CH 2 CH 3

CH 2 CH 2

CH (^2) CH
CH 3
1 2 34 5
where the symbol represents
the cyclopropyl group,
CH 3 C CH 3
CH 2
CH 3
CH CH CH 3
CH 3 CH 3
CH 3 CH CH 2
CH 3 C CH 3
CH 3
CH 3
C CCC C C
CH 3 CH 3
1234 5 67
1,3-dimethylcyclopentane can exist as
two different isomers; one with both
methyl groups on the same side of the
ring (cis-), another with the methyl
groups on opposite sides of the plane
of the ring (trans-). (See Section 27-3.)
1052 CHAPTER 27: Organic Chemistry I: Formulas, Names, and Properties
Recall that the cycloalkanes may also
be represented by the general formula
CnH 2 n.