A Guidebook to Mechanism in Organic Chemistry

Investigation of Reaction Mechanisms

o r fp Vs 1

R—C—NHBr ^ LR-C^NBr ~ R-C=NBrJ —> 0=C=N-R

(XLVIII)

But as the minimum becomes less marked, the intermediate will be­
come correspondingly less stable (b) and, therefore, less likely to be
isolable until finally the minimum is indistinguishable (c), when
transition state and intermediate become synonymous (XLIX):

(XL1X)

It should, however, be emphasised that we are not forced to rely on

actual isolation—which is a relatively rare occurrence—for the

identification of an intermediate. Physical, particularly spectroscopic,

methods supply us with a very effective and delicate alternative which

has proved immensely helpful in the investigation of reaction mech­

anisms.

INVESTIGATION OF REACTION MECHANISMS

It is seldom, if ever, possible to provide complete and entire informa­

tion about the course that is traversed by any chemical reaction: too

much is involved. Sufficient data can nevertheless often be gathered

to show that one theoretically possible mechanism is just not compa­

tible with the experimental results, or to demonstrate that one mech­

anism is a good deal more likely than another. The largest body of

work has certainly come from kinetic studies on reactions, but the

interpretation of kinetic data in mechanistic terms is not always quite