Mutual correlation between gas chromatographic retention indices of unsaturated and saturated hydrocarbons found by molecular dynamics

It is shown that gas Chromatographic retention indices for cycloalkenes can be calculated from the corresponding data for cycloalkanes (and vice versa) using computer simulation of intramolecular vibrational and rotational processes by molecular dynamics. For organic compounds structurally related asA → B, the total internal energy differences δE = E(B)-E(A) correlate with the corresponding differences in retention indices δI = I(B)-I(A), and a linear relationship exists δI =aδE + b (a < 0, |ρ| > 0.9). Limitations are found for the use of molecular dynamics for compounds havingn-alkyl radicals with no less than four carbon atoms. In these cases, a simpler model for the evaluation of dynamic molecular parameters should be preferred for the calculation of retention indices of acyclic alkenes and alkanes. The reliability of the retention indices evaluated by the proposed technique is comparable to their interlaboratory reproducibility found using standard nonpolar poly(dimethylsiloxane) stationary phases.