A Guidebook to Mechanism in Organic Chemistry

Heterocyclic Bases

CH—CH

LI*

N®

• \
  H H
  (XI)

is destabilised with respect to the neutral molecule (X); but the effect
is here more pronounced, for to function as a base pyrrole has to lose
all its aromatic character andytonsequent stability. This is reflected
in its pKb of «13 • 6 compared with 9 • 38 for aniline; it is thus only a
very weak base and functions as an acid, albeit a very weak one, in
that the hydrogen atom attached to nitrogen may be removed by a
strong base, e.g.^0 NHa.

No such considerations can, of course, apply to the fully-reduced
pyrrole, pyrrolidine ,

CH«—CHo

I I

^ /

s

which has a pK 6 of 2 • 73, closely similar to that of diethylamine, 3 * 07.