A Guidebook to Mechanism in Organic Chemistry

Structure, Reactivity and Mechanism ^

+ ®NO, + H®

In nucleophilic substitution reactions, it is often an atom other than
hydrogen that is displaced (pp. 58, 132):

NC© + R—Br

CI

HOe +

rfc-R + Br©

OH

NOs NO, *

but nucleophilic displacement of hydrogen is also known (p. 130)

H ,TlO

i N0 2 T NOs

1 + H0

though hydride ion is not actually liberated as such as will be seen
subsequently (p. 131). Radical-induced displacement reactions are also""
known, for example the halogenation of alkanes (cf. p. 248).
Addition reactions, too, can be electrophilic, nucleophilic or
radical-induced depending on whether the process is initiated by ah
electrophile, a nucleophile or a radical. Addition to simple carbon-
carbon double bonds is normally either an electrophilic or radical
reaction; an example is the addition of HBr

HBr

Br

H

which can be initiated by the attack of either He (p. 141) or Br • (p. 244)
on the double bond. By contrast, the addition reactions exhibited by

displaced, classical aromatic substitution (p. 101) being a good
example: