A reaction in which two or more unsaturated molecules (or parts of the same molecule)
combine with
the formation of a cyclic
adduct in which there is a net reduction of the bond
multiplicity. The following two systems of notations have been used for the more detailed
specification of cycloadditions, of which the second, more recent system [described
under (2)] is
preferred:
-
A(i + j + ...) cycloaddition is a reaction in which two or more molecules (or parts of
the same molecule), respectively, provide units of i, j, ... linearly connected atoms:
these units become joined at their respective termini by new σ-bonds so as to form
a cycle
containing (i + j + ...) atoms. In this notation, (a) a Diels–Alder reaction is a
(4+2) cycloaddition, (b) the initial reaction of ozone with an alkene is a (3+2) cycloaddition,
and
(c) the reaction shown below is a (2+2+2) cycloaddition. (N.B.: parentheses (...)
are used in the
description based on numbers of atoms.)
- The symbolism [i + j + ...] for a cycloaddition identifies the numbers i,
j, ... of electrons in the interacting units that participate in the transformation of
reactants to products. In this notation the reaction (a) and (b) of the preceding
paragraph would
both be described as [2+4] cycloadditions, and (c) as a [2+2+2] cycloaddition. The
symbol a or s (a
= antarafacial, s = suprafacial) is often added (usually as a subscript after the number to
designate the stereochemistry of addition to each fragment. A subscript specifying
the orbitals,
viz. σ, π (sigma, pi) with their usual significance) or n (for an orbital associated
with a single atom only), may be added as a subscript before the number. Thus the
normal Diels–Alder
reaction is a
![[ 4 s + 2 s ]](../../mathml/C01496-0.png)
or
![[ 4 s π + 2 s π ]](../../mathml/C01496-1.png)
cycloaddition, whilst the reaction:
would be a
![[ 14 a + 2 s ]](../../mathml/C01496-2.png)
or
![[ 14 a π + 2 s π ]](../../mathml/C01496-3.png)
cycloaddition. (N.B. Square brackets [...] are used in the
descriptions based on numbers of electrons.) Cycloadditions may be pericyclic
reactions or (non-concerted stepwise reactions . The term
'dipolar cycloaddition' is used for cycloadditions of 1,3-dipolar compounds.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1103
InChI=1/C7H8/c1-2-7-4-3-6(1)5-7/h1-4,6-7H,5H2
InChI=1/C6H6O4/c1-9-5(7)3-4-6(8)10-2/h1-2H3
InChI=1/C13H14O4/c1-16-12(14)10-8-5-3-4-6(8)7(4)9(5)11(10)13(15)17-2/h4-9H,3H2,1-2H3
InChI=1/C14H12/c1-2-6-10-13(9-5-1)14-11-7-3-4-8-12-14/h1-12H
SJYNFBVQFBRSIB-UHFFFAOYAK
VHILMKFSCRWWIJ-UHFFFAOYAX
YZQAUJSISPRMIU-UHFFFAOYAH
CJRANKZVJIECNW-UHFFFAOYAK
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
