Chapter 4

Problem 4-1

(a)

1,4-Dimethylcyclohexane

(b)

1-Methyl-3-propylcyclopentane

(c)

3-Cyclobutylpentane

(d)

1-Bromo-4-ethylcyclodecane

(e)

1-Isopropyl-2-methylcyclohexane

(f)

4-Bromo-1-tert-butyl-2-methylcycloheptane

Problem 4-2

(a)

In an 8-membered carbon ring, C1 is bonded to two methyl groups.

(b)

The C3 of a 6-carbon chain is bonded to a 4-membered carbon ring.

(c)

In a 5-membered carbon ring, C1 and C2 are each bonded to a chlorine atom.

(d)

In a cyclohexane ring, C1 and C3 are each bonded to a bromine atom. C5 is bonded to a methyl group.

Problem 4-3

3-Ethyl-1,1-dimethylcyclopentane

Problem 4-4

(a)

trans-1-Chloro-4-methylcyclohexane

(b)

cis-1-Ethyl-3-methylcycloheptane

Problem 4-5

(a)

In a cyclohexane ring, C1 is wedge bonded to bromine and dash bonded to hydrogen atom. C3 is wedge bonded to hydrogen atom and dash bonded to methyl group.

(b)

In a cyclobutane ring, C1 and C2 are each wedge bonded to methyl groups and dash bonded to hydrogen atoms, respectively.

(c)

In a cyclohexane ring, C1 is wedge bonded to tertiary-butyl group and dash bonded to hydrogen atom. C2 is wedge bonded to hydrogen atom and dash bonded to ethyl group.

Problem 4-6

The two hydroxyl groups are cis. The two side chains are trans.

Problem 4-7

(a)

cis-1,2-Dimethylcyclopentane

(b)

cis-1-Bromo-3-methylcyclobutane

Problem 4-8

Six interactions; 21% of strain

Problem 4-9

The cis isomer is less stable because the methyl groups nearly eclipse each other.

Problem 4-10

Ten eclipsing interactions; 40 kJ/mol; 35% is relieved.

Problem 4-11

Conformation (a) is more stable because the methyl groups are farther apart.

Problem 4-12

Two chair conformations of cyclohexanol. In the first conformation, C1 is bonded to axial hydroxyl group. In the second conformation, C1 is bonded to equatorial hydroxyl group.

Problem 4-13

Two chair conformations of trans-1,4-dimethylcyclohexane. In first conformation, C1 and C4 are each bonded to axial methyl. In second conformation, C1 and C4 are each bonded to equatorial methyl.

Problem 4-14

Before the ring-flip, red and blue are equatorial and green is axial. After the ring-flip, red and blue are axial and green is equatorial.

Problem 4-15

4.2 kJ/mol

Problem 4-16

Cyano group points straight up.

Problem 4-17

Equatorial = 70%; axial = 30%

Problem 4-18

(a)

2.0 kJ/mol (axial Cl)

(b)

11.4 kJ/mol (axial CH₃)

(c)

2.0 kJ/mol (axial Br)

(d)

8.0 kJ/mol (axial CH₂CH₃)

Problem 4-19

The less stable chair form of 1-chloro-2,4-dimethyl-cyclohexane featuring the C1 chlorine atom and C4 methyl group at axial positions, and the C2 methyl group at an equatorial position, respectively.

Problem 4-20

trans-Decalin is more stable because it has no 1,3-diaxial interactions.

Problem 4-21

Both ring-fusions are trans.