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CHAPTER 20 823 
 
O
O
O
O
R
O
O
R
H
O
O
H HO
R
O
HO
R
O
HO
R
H
HO HO
OO
O
O
R
OH
H
O
O
R
OH
HO
R
H
O
H
H
H
O
H
H
O
H
H
H
O
H
 
 
20.79. The lone pair of the nitrogen atom (of the amide group) is participating in aromaticity and is therefore 
unavailable to donate electron density into the carbonyl group. As a result, the carbonyl group is more electrophilic 
than the carbonyl group of a regular amide (where the lone pair contributes significant electron density to the carbonyl 
group via resonance). Also, when this compound functions as an electrophile in a nucleophilic acyl substitution 
reaction, the leaving group is particularly stable because it is an aromatic anion in which the negative charge is spread 
over all five atoms of the aromatic ring. With such a good leaving group, this compound more closely resembles the 
reactivity of an acid halide than an amide. 
 
20.80. 
(a) DMF, like most amides, exhibits restricted rotation about the bond between the carbonyl group and the nitrogen 
atom, due to the significant contribution of the resonance form with a C=N double bond. This restricted rotation causes 
the methyl groups to be in different electronic environments. They are not chemically equivalent, and will therefore 
produce two different signals (in addition to the signal from the other proton in the compound). Upon treatment with 
excess LiAlH4, followed by water work-up, DMF is reduced to an amine: 
 
 
 
This amine does not exhibit restricted rotation. As such, all of the methyl groups are now chemically equivalent and 
will together produce only one signal. 
(b) Restricted rotation causes the methyl groups to be in different electronic environments. As a result, the 13C NMR 
spectrum of DMF should have three signals. 
 
20.81. The first step of the synthesis involves deprotonation of the alcohol group in compound 1 using NaH, 
generating an alkoxide ion. This alkoxide ion is then treated with the chiral 2-bromo ethyl ester, to give an SN2 
reaction (note the inversion of configuration of the chiral center bearing the methyl group). Reduction of the ester with 
DIBAH provides an aldehyde, which is transformed into the terminal olefin (compound 2) using a Wittig reaction. 
 
 
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