CHEM 255
Chapter 4 Quiz 2 Name: ___________________________________
Newman projections
1. The three staggered forms of 1,2-propanediol are represented here (I, II, and III). Their
order of relative stability is more stable I>III>II less stable. Offer an explanation for this
apparent inconsistency with what we have discussed in class.
OH
CH3
H
H
OH
H
H
OH
H3C
H
OH
H
CH3
H
HO
H
OH
H
I. II. III.
Answer:
In class we have discussed that large groups prefer to be staggard-anti to each other to
minimize steric(gauche) interactions. In this problem H-bonding is very important, and
there are strong interactions from 1,2-diols. Structure I is the most stable due to the fact that
large groups are anti to each other and diols are close to each other which allows strong H-
bonding between OH groups. Despite the fact that III has larger groups in gauche positions
instead of anti to each other, the H-bonding from the diols makes up for this gauche
instability. The inconsistency is in this case is that H-bonding from 1,2-diols is strong
enough to overcome the prejudice of large groups wanting to reside anti to each other to
minimize steric effects.
2. Provide the Newman projection for this molecule from the prescribed point of view.
point of
view
OCH
3
CH
2
CH
3
PhH
2
CO
H
3
C
H
H
Answer:
Here is Newman project from above perspective
CH
2
CH
3
OCH
3
H
H
3
C
H
OCH
2
Ph
