Organic Chemistry Basics 2 Question 51
51. Among $P, Q, R$ and $S$, the aromatic compounds(s) is/are
(a) $P$
(b) $Q$
(c) $R$
(d) $S$
(2013 Adv.)
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Solution:
- PLAN A species is said to have aromatic character if (a) ring is planar
(b) their is complete delocalisation of $\pi$-electrons
(c) Huckel rule i.e. $(4 n+2)$ rule is followed. where, $n$ is the number of rings
$(4 n+2)=\pi$ electron delocalised.
| $n$ | $(4 n+2)$ | $\pi$ electrons | ||
|---|---|---|---|---|
| $\mathrm{P}$ | - | 0 | 2 | 2 |
| $\mathrm{Q}$ | - | 1 | 6 | 6 (including lone pair) |
| $\mathrm{R}$ | - | 1 | 6 | 6 (including lone pair on $\mathrm{N})$ |
| $\mathrm{S}$ | - | 1 | 6 | 6 |
In all cases there is complete delocalisation of $\pi$-electrons.
