InterviewSolution
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InterviewSolution
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What is the correct order of `o//p` ration when `E^(+)` attackes the following system ? (A) `PhF` (B) `PhCl` (C) `PhBr` (D) `PhI`A. `A lt B lt C lt D`B. `A = B = C = D`C. `D lt C lt B lt A`D. `D lt B lt A lt C` |
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Answer» Correct Answer - A 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. |
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