Molecular structure and conformations of bicyclopentyl, C5H9C5H9, as studied by electron diffraction, molecular mechanics and ab initio methods

Abstract The molecular structure of bicyclopentyl was established by gas phase electron diffraction, and it is compared with that calculated previously by molecular mechanics (MM3) and currently by ab initio methods (6–31G ∗ ). There is good agreement between theory and experiment for the structural parameters, and the conformational ratio, measured with a low precision, is in fair agreement with that calculated by both methods. Experiment and theory agree that the major conformer is equatorial, equatorial, anti (ee, anti). Comparisons are made with conformations of similar bicyclic (bicyclopropyl, bicyclobutyl and bicyclohexyl) and open-chain (sym-tetramethylethane) compounds. The main structural parameters measured for the ee, anti conformer are as follows: CC ave , 1.541(4) A; CH, 1.121(12) A; bond angles: C 2 C 1 C 5 , 103.7(3)°; C 1 C 2 C 3 , 107.9(5)°; C 2 C 1 C 6 , 113.3(3)°; CCH, 112.7(10)°; HCH 106.3(8) A. Additionally, the CC bond length between the rings is assessed to be 1.545(10) A. Similar bond lengths in related bicyclic molecules are found to correlate with the ring CCC bond angles.