Chemistry Reference
In-Depth Information
Problem 16.03 (level 1; chapters 3 and 7)
(a) Indicate, with appropriate comments, which of the following compounds could exist in optically active form:
OH
OH
OH
OH
(b) Draw the compound cinerolone to show the shape of its ring and other stereochemical features.
CH
3
HO
Z
CH
2
CH=CHCH
3
O
cinerolone
(c) Reduction of menthone with sodium borohydride gives menthol and a second isomeric material, neomenthol.
Give a mechanism for the reaction and suggest a structure for neomenthol.
O
OH
menthone
menthol
What is the relationship of neomenthol to menthol? Is it a structural isomer, a configurational isomer, a
diastereoisomer, an epimer, a
meso
compound, a conformer? Several of these terms may apply.
Answer 16.03
(a) This is a 'spot the chiral centre' problem. A chiral centre has four different groups attached; we must also
bear in mind that a
meso
compound has chiral centres, but the compound itself is optically inactive. This
arises because the molecule has a plane of symmetry, and optical activity conferred by one chiral centre is
equal and opposite to that conferred by the other, and is therefore cancelled out.
plane of
symmetry
aromatic ring is
planar
* = chiral centre
OH
*
*
*
OH
OH
OH
1 chiral
centre
no chiral
centres
1 chiral
centre
1 chiral
centre
no chiral
centres
no chiral
centres
