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Unformatted text preview: form of benzene. We say that one ring is benzenoid, and the other is not. By rewriting the benzenoid ring in its alternative Kekul form, both rings become benzenoid. ( b ) Here a cyclobutadiene ring is fused to benzene. By writing the alternative resonance form of cyclobutadiene, the six-membered ring becomes benzenoid. Both rings are benzenoid. This six-membered ring is not benzenoid (does not correspond to Kekul form of benzene). This six-membered ring is benzenoid (corresponds to a Kekul form of benzene). Less stable More stable CH CH 2 140 pm 147 pm 134 pm Cl Cl p-Dichlorobenzene m 5 0 D m-Dichlorobenzene m 5 1.48 D Cl Cl o-Dichlorobenzene m 5 2.27 D Cl Cl 264 ARENES AND AROMATICITY...
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- Fall '01
- Organic chemistry