partial rate factor
The rate of substitution at one specific site in an @A00441@ compound relative to the rate of substitution at one position in benzene. For example, the partial rate factor \(f_{p}^{\text{Z}}\) for para-substitution in a monosubstituted benzene C6H5Z is related to the rate constants \(k\left(\text{C}_{6}\text{H}_{5}\text{Z}\right)\) and \(k\left(\text{C}_{6}\text{H}_{6}\right)\) 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: \[f_{p}^{\text{Z}} = \frac{6\ k\left(\text{C}_{6}\text{H}_{5}\text{Z}\right)}{k\left(\text{C}_{6}\text{H}_{6}\right)}\ \frac{\%\ \text{para}}{100}\] Similarly for meta-substitution: \[f_{m}^{\text{Z}} = \frac{6\ k\left(\text{C}_{6}\text{H}_{5}\text{Z}\right)}{2\ k\left(\text{C}_{6}\text{H}_{6}\right)}\ \frac{\%\ \text{meta}}{100}\] (The symbols \(p_{f}^{\text{Z}}\), \(m_{f}^{\text{Z}}\), \(o_{f}^{\text{Z}}\) are also in use.) The term applies equally to the ipso position, and it can be extended to other substituted substrates undergoing @P04403@ at different sites with the same @R05190@ according to the same @R05141@.
See also:
selectivity (of a reagent)
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1149 [Terms] [Paper]