The steric demand of `H^Theta` is, however, extremely small, and when attack on `C_6H_5Y` is by any other electrophile, `E^Theta ` , 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 `Delta 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 `f_(o^-)//f_(p^-)` ratios which are observed for the nitration of alkylbenzenes `(Y - CH_3 to CMe_3)` under comparable conditions ,
