16-32 continued H H (h) H H CH3 I I I (B is sp2, but 0 +C C-B donates no 0 0 0 electrons to the 1t system) nonaromatic aromatic-anti aromatic-aromatic-6 1t electrons 8 1t electrons 6 1t electrons 16-33 The clue to azulene is recognition of the five- and seven-membered rings. To attain aromaticity, a seven-membered carbon ring must have a positive charge; a five-membered carbon ring must have a negati ve charge. Drawing a resonance form of azulene shows this: OJ --.. ---. C» --.. ---� ri:�sance } <[email protected]composite picture The composite picture shows that the negative charge is concentrated in the five-membered ring, giving rise to the dipole. 16-34 Whether a nitrogen is strongly basic or weakly basic depends on the location of its electron pair. If the electron pair is needed for an aromatic 1t system, the nitrogen will not be basic (shown here as "weak
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