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8.4. Organic chemistry reaction mechanism — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistry8.4. Organic chemistry reaction mechanism1 Mark
MCQ
Which compound posses highest dipole moment ?
  • A
    naphthalene
  • B
    phenanthrene
  • C
    anthracene
  • ✓
    azulene
✓

Answer

Correct option: D.
azulene
d
$(d)$ Polycyclic systems : Huckel's $(4n + 2)$ rule applies to monocyclic systems. The  rule, however, is not necessarily successful for p'olycyclic 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 $1^{st}-$electrons are common to both rings). If one $\pi$ - electron is transferred from the seven - to the five - ring, each ring will now have a  closed shell of six $\pi$ - 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. 

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