In the above reaction o/p ratio will be highest when :

The steric demand of ${\mathrm{H}}^{\ominus }$ is, however, extremely small, and when attack on C₆H₅Y is by any other electrophile, ${\mathrm{E}}^{\oplus }$, which will necessarily be larger, there will be increasing interaction between E and Y in the transition state for attack at the position o- to Y (57 b, R = E) as attacking electrophile and substituent increase in size ; there can be no such interaction in the transition state for p- attack (57a, R = E). This will be reflected in an increasing $∆$G⁺ for o- attack, a consequently slower reaction, and the relative proportion of o- product will thus fall as the size of E and / or Y increase. This is illustrated by the falling ${\mathrm{f}}_{{\mathrm{o}}^{-}}/{\mathrm{f}}_{{\mathrm{p}}^{-}}$ ratios which are observed for the nitration of alkylbenzenes (Y - CH3 → CMe₃) under comparable conditions ;