Application of a semi-homodesmotic approach in estimating ring strain energies (RSEs) of highly substituted cyclobutanes: RSEs for c-C4R8 that make sense.

Thomas M Gilbert

The journal of physical chemistry. A 2014 Aug 7

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A semi-homodesmotic method for estimating of ring strain energies (RSEs) of substituted cyclopropanes is applied to substituted cyclobutanes c-C4HxR8-x (R = F, Cl, Me; x = 0, 2, 4). Whereas (hyper)homodesmotic reaction methods predict implausible results, particularly for c-C4R8, the semi-homodesmotic approach provides RSEs consistent with thermodynamic and independent computational data regardless of the degree of substitution. The method requires employing homodesmotic group equivalent reactions only for disubstituted cyclobutanes, relying solely on absolute energy calculations for more substituted rings. We find that, consistent with QTAIM data, RSEs increase with substitution regardless of the electronic nature of R, although the increase is more dramatic when R is electron-withdrawing. Overall, the semi-homodesmotic method is simpler than hyperhomodesmotic approaches and gives more trustworthy results.

Citation

Thomas M Gilbert. Application of a semi-homodesmotic approach in estimating ring strain energies (RSEs) of highly substituted cyclobutanes: RSEs for c-C4R8 that make sense. The journal of physical chemistry. A. 2014 Aug 7;118(31):6060-7