That the steric factor is not the sole determinant is, however, seen in the figure for the nitration of the halobenzenes, which are `o//p-`directing but on which overall attack is slightly slower than on benzene.
`"Increase in size of Y"darr{:(Y,%o-,%p-,),(F,12,88,),(Cl,30,69,),(Br,37,62,),(I,38,60,):}`
Despite the increase in size of the substituent Y from `F rarr I`, the proportion of `o-`isomer increase. An increasing steric effect will, as with the alkyl benzenes, be operating to inhibit `o-`attack, but this must here be outweighed by the electron-withdrawing inductive/field effect exerted by the halogen atom (Y). This effect will tend to decrease with distance from Y, being exerted somewhat less strongly on the distant `p-`position thus takes place on `C_(6)H_(5)F`, despite the small size of F. The electron -withdrawing effect of the halogen (Y) decrease considerably from F to I (the biggest change being between F and Cl), resulting in increasing attack at the `o-`position despite the increasing bulk of Y.
