1,1-Diamino-2,2-bis(triflyl)ethylenes with both twisted and planar structures around the partial "C=C" bond were synthesised. Bonding properties in these compounds were analysed by an experimental approach using high-resolution X-ray diffraction data treated with X-ray wavefunction refinement (XWR). In the twisted compound, a dominant contribution of the charge-separated resonance structure was revealed. On the contrary, the nearly planar compound still showed π-bonding character, however, with a considerable contribution of the charge-separated resonance structure.
Keywords: alkenes; carbanions; complementary bonding analysis; quantum crystallography; zwitterions.
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