6. 1. 0.

Article abstract of DOI:10.1021/ja00318a032

The enthalpies of formation of cis- and trans-1,2-diethylcyclopropane were determined by oxygen bomb calorimetry. The cis-diethyl isomer was 1. 1 kcal/mol less stable than the trans isomer. Alkyl groups were found to stabilize a cyclopropane ring by the same amount as for a carbon-carbon double bond. The enthalpies of formation cis- and trans-bicyclo left bracket 6. 10 right bracket nonane also were determined by oxygen bomb calorimetry. The two bicyclo left bracket 6. 1. 0 right bracket nonanes have essentially the same enthalpies of formation, in contrast to cis- and trans-cyclooctene. The introduction of a trigonal center makes the trans-bicyclononane 3 kcal/mol less stable than the cis isomer. Molecular mechanics calculations are reported for a series of cis- and trans-bicyclo left bracket n. 1. 0 right bracket alkanes. In order to better estimate the strain energy of trans-bicyclo left bracket 4. 1. 0 left bracket heptane, the difference in energy between it and its cis isomer was calculated via ab initio molecular orbital theory.