Cis-substituted alkenes are usually less stable than their trans-substituted counterparts. However, cis-2-butenyl anion is known to be more stable than the corresponding trans-isomer. We suggest that two cooperating factors stabilize the cis anion: through-space interactions between the anionic center and methyl group, and through-bond coupling via the C=C pi* orbital. The through-bond effects are known in other attractive nonbonded interactions, including the anomalous stability of cis 1,2-difluoroethylene. The proposed through-space effects are consistent with computed substituent effects on the cis stabilization. Through-bond effects are consistent with calculations varying the C=C pi* orbital energy via bond stretching.

Through-space and through-bond stabilization of cis alkenyl anions

253rd National Meeting (2017)

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