Which compound posses highest dipole moment ?

Options

A. naphthalene
B. phenanthrene
C. anthracene
D. azulene

Answer

D

Explanation

Polycyclic systems : Huckel.s (4n + 2) rule applies to monocyclic systems. The rule, however, is not necessarily successful for polycyclic conjugated systems,

the (4n+2) rule should be applied to the peripheral (conjugated) `pi` -electrons. The five-membered ring has five and the seven-membered ring has seven `pi` -electrons (two TE-electrons are common to both rings). If one T-electron is transferred from the seven - to the five - ring, each ring will now have a closed shell of six t-electrons (cf. naphthalene). In this condition, the molecule will have a dipolar structure, and this has been shown to be the case from dipole - moment measurements. Azulene also behaves chemically as an aromatic compound.