Test Bank For Organic Chemistry 8th Edition By L. G. Wade

Chapter 7   Structure and Synthesis of Alkenes

1) Which of the following statements best describes the relative bond dissociation energies of the sigma and pi bonds present in the carbon-carbon double bond of an alkene?

A) sigma > pi

B) pi > sigma

C) sigma = pi

D) cannot be estimated

Answer:  A

Diff: 2

Section:  7.1

2) The carbon-carbon bond length in ethylene is ________ than the carbon-carbon bond length in ethane, and the HCH bond angle in ethylene is ________ the HCH bond angle in ethane

A) shorter; smaller than

B) shorter; larger than

C) longer; smaller than

D) longer; larger than

E) longer; the same as

Answer:  B

Diff: 1

Section:  7.2

3) Carbon-carbon single bonds tend to be ________ and ________ than carbon-carbon double bonds.

A) shorter, stronger

B) longer, stronger

C) shorter, weaker

D) longer, weaker

Answer:  D

Diff: 1

Section:  7.2

4) Which of the following best approximates the CCC bond angle of propene?

A) 90°

B) 109°

C) 120°

D) 150°

E) 180°

Answer:  C

Diff: 1

Section:  7.2

5) Circle all atoms that are coplanar in the molecule below.

Answer:

Diff: 2

Section:  7.2

6) Draw the line energy orbital diagram for the outer shell of an sp2 hybridized carbon atom and explain how a carbon/carbon double is formed.

Answer:

If we follow Hund’s rule and fill each orbital with one electron and then promote one to the lone atomic p orbital, there are single electrons in the three sp hybrid orbitals that can form sigma overlaps with 2-H orbitals and one other sp2 hybridized carbon orbital.  The atomic p orbital with one electron can then form a pi bond by a side to side overlap with the other p orbital from the other sp2 hybridized carbon atom.

Diff: 2

Section:  7.2

7) Why is rotation about the carbon-carbon double bond in alkenes prohibited while relatively free rotation can occur about the carbon-carbon single bond in alkanes?

Answer:  Rotation about the C