Selection of Standard Conditions

As in hydrogen exchange (Chapter 2, Section 1. G), evaluation of standard nitration rates permits comparison of substrate reactivities under the same conditions. Previous comparisons between nitration rates of compounds of widely differing reactivity have required a stepwise procedure (71 Mil), which carries the implicit assumption that partial rate factors do not vary appreciably with acidity. 

The definition of standard conditions is more difficult for nitration than for hydrogen exchange because of uncertainty in the NO,+ activity variation, and the peculiar behavior of benzene itself. The standard conditions chosen were 25°C and H0 -6.6 (i.e., 75 wt% H2S04 at 25°C) [75JCS(P2)I600]. The choice of 25°C was made because kinetics for many nitrations have been followed at this temperature, and most in the range 0-100°C. The standard acidity of H0 -6.6 minimizes the extrapolations needed for the rate profiles of many substrates and is close to the range of normal behavior found for benzene. 

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