Intramolecular van der Waals interactions and ¹³C chemical shifts: Substituent effects in some cyclic and bicyclic systems

In recent work, a reasonably good linear correlation was found to exist between the local van der Waals steric energy as calculated by the MM2 force field and the chemical shift of the resonant nucleus within classes of saturated aliphatic phosphines, amines, hydrocarbons and monofunctional alcohols. This study extends this work to some additional cyclic systems: 91 trans ‐ and 31 cis ‐decalin carbons, 57 bicyclo[2.2.1]heptane and 27 bicyclo[2.2.2]octane nuclei have been investigated and yield root‐mean‐square errors of 3.3–3.7 ppm and correlation parameters in good agreement with those found previously for other carbon species. In the more strained bicyclo systems it is found that additional class parameters must be defined. The theory is applied to a variety of α,β,γ,… ubstituents effects in cyclohexane and decalin systems, and correlated these resonant shifts under one simple, physical model.