MM2' calculations on methylenecyclohexane, methylenecyclopentane, and cyclopentane. Pitfalls in the two‐bond drive technique: How large should the ring be?

Molecular mechanics calculations (MM2') are reported on methylenecyclohexane, 1, methylenecyclopentane, 2, and cyclopentane itself, 3. The calculated torsional energy barrier for the chair/chair interconversion of 1 if 8.7 kcal/mol (experimental ΔH ≠ = 8.4 ±0.1 kcal/mol); compounds 2 and 3 have virtually free pseudorotational pathways (calculated ΔH ≠ = 2.33 and 0.008 kcal/mol, respectively). Copyright © 1990 John Wiley & Sons, Inc.