• # question_answer 26) Explain why the following systems are not aromatic? (i) (ii) (iii)

(i) Due to the presence of $s{{p}^{3}}$ -hybridized carbon, the system is not planar. It contains six $\pi$-electrons but the system is not fully conjugated since all the six $\pi$-electrons do not form a single cyclic electron cloud. Therefore, it is not an aromatic compound. (ii) $(4n+2)$$\pi$ -electron (Huckels rule) is not applicable. It contains only four electrons and dueto the presence of a $s{{p}^{3}}$ -carbon, the system is not planar. Therefore, the system is not aromatic. (iii) It is a non-planar system having eight $\pi$-electrons. It does not contain a planar cyclic cloud having $(4n+2)$$\pi$-electrons. Therefore, the molecule is not aromatic.