Estimating Ring Strain Energies of Highly Substituted Cyclohexanes with the Semi-homodesmotic Approach: Why Substantial Ring Strain Exists for Nominally Tetrahedral Ring Carbon Atoms.

Estimation of ring strain energies (RSEs) of substituted cyclohexanes c-C6H(x)R(12-x) (R = F, Cl, Me; x = 0, 2, 4, 8, 10, 12) using homodesmotic reaction methods gives implausible results for highly substituted cases, particularly, c-C6R12. Prior work suggests that this stems from poorly canceled interactions between substituents on the acyclic reference molecules. We apply here our semi-homodesmotic approach that minimizes use of acyclic references and ensures cancellation of intramolecular substituent interactions.

A semi-homodesmotic approach for estimating ring strain energies (RSEs) of highly substituted cyclopropanes that minimizes use of acyclic references and cancels steric interactions: RSEs for c-C3R6 that make sense.

Estimation of ring strain energies (RSEs) of substituted cyclopropanes c-C(3)H(x)R(6-x) (R = F, Cl, Me; x = 0, 2, 4) using homodesmotic reaction methods has been plagued by implausible results. Prior work suggests that this stems from poorly canceled interactions between substituents on the acyclic reference molecules. We report a semi-homodesmotic approach that minimizes use of acyclic references, focusing instead on canceling substituent interactions.

Computational studies of Lewis acidities of tris(fluorophenyl)-substituted boranes: an additive relationship between Lewis acidity and fluorine position.

Computational studies of the binding energies of all possible tris(fluoroaryl)boranes B(C(6)H(x)F(5-x))(3) to NMe(3) and PMe(3) show that they (and by extension, the Lewis acidities of the boranes) can be tuned to a sizable range of values through judicious placement of fluorines. This holds despite the fact that the B-X bond distance changes little regardless of substitution, save when the aryl ring is 2,6-disubstituted. Fluorine substitution appears to affect the binding energies additively.