The structure of bicyclo[3.1.0]hexane as determined by electron diffraction and microwave spectroscopy. Reinvestigation with ab initio calculations. Calculated structure of bicyclo[4.1.0]heptane

The molecular structure of bicyclo[3.1.0]hexane determined in 1977 by one of us, is now reinvestigated in view of critical comments which appeared in 1982 by Skancke 1 , in 1984 by Traetteberg et al. 2 and in 1987 by Siam et al. 3 Original experimental data were used in a combined analysis augmented by our ab initio calculations made with the 6-31G∗ basis set. As a result of this study, the previously determined very short intra-annular CC bond distance of 1.454(9)A became 1.510(2)A, in accordance with ab initio calculations. In order to extend the series of bicyclo[ n .1.0]alkanes ( n = 1, 2 and 3) studied theoretically by Skancke, ab initio calculations were also performed for bicyclo[4.1.0]heptane using the STO-3G, 3-21G∗, 4-31G, 6-31G and 6-31G∗ basis sets.