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SolutionsConformations (Rotamers)

Draw Newman projections of the conformers of ethane, propane, and 2-methylpropane, as well as their expected conformational energy profiles.

Solution: conformations of ethane and their energy profile (3 kcal/mol barrier)
Solution: conformations of propane and their energy profile (3.4 kcal/mol barrier)
Solution: conformations of 2-methylpropane and their energy profile (3.8 kcal/mol barrier)

What isomerism relationship do the indicated structures have:

Two structures in Newman projection bearing Ph, CH₃ and H

A) they are not isomeric
B) conformational isomers
C) cis-trans isomers
D) structural isomers
E) rotamers
F) both B and D
G) both B and E

G) both B and E

Which answers are correct regarding the indicated structures:

Two structures in Newman projection bearing two methyl groups

A) they are not isomeric
B) conformational isomers
C) non-superimposable object and mirror image
D) object and mirror image interconvertible by rotation of the central link
E) all of the above
F) all of the above except A

F) all of the above except A

Perform the conformational analysis of 2-methylbutane

Solution: conformational analysis of 2-methylbutane; the staggered conformations have one or two CH₃/CH₃ gauche interactions

Among the conformers of butane, say which statements are correct:

A) only gauche conformations are energy minima
B) the eclipsed ones are low in energy
C) the gauche and anti conformations are energy minima
D) the conformation with the eclipsed methyl groups is the highest in energy
F) the anti conformation is the lowest in energy
G) all of the above except B

C) D) F)