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Updated: Aug 8, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Equilibrium structures for butadiene and ethylene: compelling evidence for pi-electron delocalization in butadiene
Norman C Craig1, Peter Groner, Donald C McKean
1Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074, USA.
Abstract:
Equilibrium structures have been determined for s-trans-1,3-butadiene and ethylene after adjusting the rotational constants obtained from rotational spectroscopy by vibration-rotation constants calculated from the results of quantum chemical calculations. For butadiene, the formal C=C bond length is 1.338 A, and the formal C-C bond length is 1.454 A. For ethylene, the C=C bond length is 1.3305 A. These values appear to be good to 0.001 A. It is shown for the first time that pi-electron delocalization has the structural consequences of increasing the length of the formal double bond by 0.007 A and decreasing the length of the formal single bond by 0.016 A. Comparisons are made with structures computed with several quantum chemical models. The MP2/cc-pVTZ results agree best with the new re structure.
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