Chapter 25 Suggested Homework Answers

Exercises 8, 12, 20, 21, 22, 39, 40, 61, 62, 64

8. Singly bonded carbon atoms have sp³ hybridization. Doubly bonded carbon atoms have sp² hybridization. Triply bonded carbon atoms have sp hybridization. For the given molecule, the hybridization on the carbon atoms are as follows:

12. (a) An alkane has singly bonded carbon atoms only with no rings of carbon atoms.

(b) A cycloalkane has singly bonded carbon atoms only with at least one ring of carbon atoms.

(c) An alkene contains at least one carbon-carbon double bond.

(d) An alkyne contains at least one carbon-carbon triple bond.

(e) Aromatic hydrocarbons consist of 6-membered carbon rings with alternating single and double bonds which undergo resonance.

20. (a) A carbon in an alkane has sp³ hybridization.

(b) The carbon in a double bond in an alkene has sp² hybridization.

(c) The carbon in a benzene ring has sp² hybridization.

(d) The carbon in a triple bond in an alkyne has sp hybridization.

In each of the structural drawings, the numbering system for the longest continuous chain of carbon atoms is notated by italicized numbers next to each of the carbons in the chain. Generally, the structural formula will not contain these italicized numbers.

21. (a)

The longest continuous chain of carbon atoms is 6 carbons long (numbered above) so this is a “hexane”

There is a methyl group on carbon number 2: 2-methylhexane

(b)

The longest continuous chain of carbon atoms is 10 carbons long so this is a “decane”

There is an ethyl group on carbon number 4 and two methyl groups: one at carbon 2, the other at carbon 4:

4-ethyl-2,4-dimethyldecane.

(c) 3-methylhexane

The “hexane” refers to a six-membered continuous chain of carbon atoms. There is a methyl (-CH₃) group on carbon number 3:

(d) 4-ethyl-2,2-dimethyloctane

The “octane” refers to an eight-membered continuous chain of carbon atoms. There is an ethyl (-CH₂CH₃) group on carbon number 4 and two methyl groups (-CH₃) on carbon number 2:

(e) methylcyclohexane

Cyclohexane is a 6-membered carbon ring with a formula of C₆H₁₂. In methylcyclohexane, one of the H’s has been replaced with a methyl group (-CH₃):

22. (a)

The longest continuous chain of carbon atoms is seven carbons long. This is a “heptane.

There are three methyl groups, two on carbon number 3 and one on carbon number 5.

This is 3,3,5-trimethylheptane.

(b)

The longest continuous chain of carbon atoms is seven carbons long. This is a “heptane.”

There are 3 methyl groups, one on carbon number 3 and two on carbon number 4.

This is 3,4,4-trimethylheptane.

(c) 2,5-dimethylnonane.

Nonane is a continuous chain of 9 carbon atoms. There are methyl groups on carbon numbers 2 and 5. The structure is:

(d) 3-ethyl-4,4-dimethylheptane.

Heptane is a continuous chain of 7 carbon atoms. There is an ethyl group (-CH₂CH₃) on carbon number 3. There are two methyl groups, each on carbon number 4. The structure is:

(e) 1-ethyl-4-methylcyclohexane

Cyclohexane is a six-membered ring of carbon atoms. On the 1^st carbon, there is an ethyl group. On the 4^th carbon atom, there is a methyl group:

39. (a) ketone

(b) carboxylic acid

(c) alcohol

(d) ester

(e) amide

(f) amine

40. The functional group names are italicized next to the functional group in each of the structures:

(a)

(b)

(c)

(d)

(e)