question_answer

Which of the following do not obey Huckels rule for aromaticity?

A)  I, IV                                      

B)  I, II

C)  III, IV                                   

D)  All of these

Correct Answer: C

Solution :

                 According to Huckel s rule for aromaticity, a compound must follow following rules : (i) It must be cyclic and planar. (ii) It must have a conjugated system in it (iii) It must have \[(4n+2)\pi \] n electrons. (i) In, no. of \[\pi \]electrons = 6 \[(4n+2)=(4\times 1+2)=6,\]thus Hukels rule is followed. (ii) no. of \[\pi \]electrons \[=4+2=6\] \[(4n+2)=(4\times 1+2)=6,\]thus Huckels rule is followed.   no. of \[\pi \]electrons = 4 \[(4n+2)\ne 4,\]thus Huckles rule is not followed   no. of\[\pi \]electrons = 4 \[(4n+2)\ne 4,\]thus Huckels rule is not followed.