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partial rate factor

The rate of substitution at one specific site in an aromatic compound relative to the rate of substitution at one position in benzene. For example, the partial rate factor f p Z for para-substitution in a monosubstituted benzene C6H5Z is related to the rate constants k C 6 H 5 Z and k C 6 H 6 for the total reaction (i.e. at all positions) of C6H5Z and benzene, respectively, and % para (the percentage para-substitution in the total product formed from C6H5Z) by the relation:
f p Z = 6 k C 6 H 5 Z k C 6 H 6 % para 100
Similarly for meta-substitution:
f m Z = 6 k C 6 H 5 Z 2 k C 6 H 6 % meta 100
(The symbols p f Z, m f Z, o f Z are also in use.) The term applies equally to the ipso position, and it can be extended to other substituted substrates undergoing parallel reactions at different sites with the same reagent according to the same rate law.
See also: selectivity
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1149
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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: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
Last update: 2014-02-24; version: 2.3.3.
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