Weblink 4.5 The π bonding MO of ethene as a function of torsion angle

This is an illustration of the effect of rotation about the C-C bond of ethene on the π MO formed from the overlap of the unhybridized 2p AOs. In the planar geometry, there is good overlap between the 2p AOs, but if one of the CH₂ groups is twisted by 45°, there is clearly poorer overlap. Twisting the group by 90° results in essentially no overlap between the AOs: the π bond is therefore broken.

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