Page 350 - Mechanism and Theory in Organic Chemistry

Chapter 7

ADDITION AND

--
ELIMINATION

REACTIONS

In this chapter we shall discuss the destruction and formation of carbon-carbon
multiple bonds by addition and elimination reactions, respectively. The mech-
anism of aromatic substitution in which addition and elimination occur as
separate steps will also be discussed.

7.1 ELECTROPHILIC ADDITION TO
DOUBLE AND TRIPLE BONDS1
Carbon-carbon .rr bonds are relatively weak ( - 65 kcal/mole-l). They are also,
unless substituted by strong electron-withdrawing groups, electron-rich. For
these reasons addition to them by electrophilic reagents usually occurs readily.
The exact m_ech&sm of addition depends on the reagent.
-

Hydration
The acid-catalyzed addition of water to a double bond is kinetically second-
order, first-order each in olefin and in H30 + .2 This fact is equally consistent with
the concerted addition of a proton and a water molecule from the same H30+
and with initial attack of a proton to one side of the double bond followed by

(a) P. B. D. de la Mare and R. Bolton, Electrophilic Additions to Unsaturated Systems, Elsevier, Amster-
dam, 1966; (b) R. C. Fahey, in Topics in Stereochemisty, E. L. Eliel and N. L. Allinger, Eds., Wiley-
Interscience, New York, 1968, Vol. 3, p. 237; (c) R. Bolton, in Comprehensive Chemical Kinetics,
C. H. Bamford and C. F. H. Tipper, Eds., Elsevier, New York, 1973, Vol. 9, chap. 1.
See note 1 (a). .