CH 3 Multiple Choice

At room temperature, the various conformations of butane:

A. do not interconvert; only the anti form is present.

B. do not interconvert, but all conformations are present.

C. interconvert very slowly.

D. interconvert very rapidly.

Predict which of the following constitutional isomers of C5H10 would have the highest heat of combustion?

A. methylcyclobutane

B. cyclopentane

C. cis-1,2-dimethylcyclopropane

D. trans-1,2-dimethylcyclopropane

Cyclohexane adopts the chair conformation rather than a planar structure because:
I. torsional strain is minimized. II. the C—C—C bond angles are close to 109.5o. III. there are no 1,3-diaxial interactions in a planar structure.

A. only I

B. only II

C. I and II

D. I, II, and III

The most stable chair conformation of cis-1-tert-butyl-3-methylcyclohexane has

A. both groups equatorial.

B. both groups axial.

C. the tert-butyl group equatorial and the methyl group axial.

D. the tert-butyl group axial and the methyl group equatorial.

Which statement below is true concerning the conversion of cis-1,4-dimethylcyclohexane to trans-1,4-dimethylcyclohexane?

A. The conversion takes place by chair conformation ring-flipping.

B. You cannot do the conversion without breaking covalent bonds.

C. The conversions takes place by rotating the C(1)─C(2) bond by 180°.

D. The conversion takes place through the skew boat conformations.

What would the C—C—C bond angles be in a planar cyclohexane?

A. 60°

B. 90°

C. 109.5°

D. 120°

Which constitutional isomer of dimethylcyclohexane does not exhibit cis-trans isomerism?

A. 1,1-dimethylcyclohexane

B. 1,2-dimethylcyclohexane

C. 1,3-dimethylcyclohexane

D. 1,4-dimethylcyclohexane

Which one of the following is not a constitutional isomer of trans-1,3-dimethylcyclopentane?

A. 1,1-dimethylcyclopentane

B. cis-1,2-dimethylcyclopentane

C. ethylcyclopentane

D. cis-1,3-dimethylcyclopentane

Which of the following can have cis-trans stereoisomers?

A. 1,1-dimethylcyclobutane

B. 1,3-dimethylcyclobutane

C. 1,1,3-trimethylcyclobutane

D. 1,1,3,3-tetramethylcylclobutane

The C—C—C bond angle in cyclopropane is

A. 60°.

B. 90°.

C. 109.5°.

D. 120°

The most stable conformation of cis-4-methyl-1-tert-butylcyclohexane is a chair conformation with

A. both the -CH3 and -C(CH3)3 equatorial.

B. both the -CH3 and -C(CH3)3 axial.

C. the -CH3 equatorial and the -C(CH3)3 axial.

D. the -CH3 axial and -C(CH3)3 equatorial.

Which is more stable, cis-1,3-dimethylcyclohexane or trans-1,3-dimethylcyclohexane?

A. trans-1,3-dimethylcyclohexane

B. cis-1,3-dimethylcyclohexane

C. They are equally stable.

D. Stabilities of cis, trans stereoisomers cannot be compared.

Which is the least stable of the Newman Projections?

A. Gauche

B. Eclipsed

C. Anti

D. Newman

What conformation of butane is most stable?

A. Eclipsed

B. Anti

C. Gauched

D. Newman

2,3-dimethylbutane