Structures of strained polycyclics: Bond distances and angles in tricyclo[3.3.0.0 2,6]oct-3-ene and in bicyclo[2.1.1]hexene-2

Abstract

The structure of tricyclo[3.3.0.0 2,6]oct-3-ene in the gas phase has been determined by electron diffraction. From least squares fitting of theoretical to the experimental intensity function (range: 6 ⩽ q ⩽ 106), the CC bond lengths in the cyclobutane ring were found to be 1·580 ± 0·015 Å. In the 5-member ring which contains the double bond, the CC distances are 1·503 ± 0·012 Å, and in the other 5-membered ring, they are 1·505 ± 0·018 Å on the sides and 1·579 ± 0·038 Å at the base. The CC bond is 1·345 ± 0·010 Å, and the average CH separation is 1·128 ± 0·010 Å. The recorded patterns for the bicyclo[2.1.1]hexene-2 covered the angular range of q = 12−125 Å −1. The interatomic distances and bond angles were obtained by applying a least squares analysis to the experimental molecular intensities. The CC double bond length was found to be 1·332 +- 0·005 Å; CC single bond, adjacent to the double bond, is 1·537 ± 0·008 Å, while the sp 3 -hybrid CC single bond is 1·549 ± 0·006 Å. The dihedral angle of the 4-membered ring is 123·5 ± 1·3°. Comparison of the structures reported for this family of polycyclic hydrocarbons concludes this paper.