Combined Electron-Diffraction and Spectroscopic Determination of the Structure of Spiropentane, C₅H₈

Abstract

Gas-phase electron-diffraction (GED) data have been combined with recent spectroscopic rotational constants to determine the r structural parameters for spiropentane, CH. The structure has D symmetry, and the results yield values of 1.105(2) Å for the CH bond length, 1.557(3) Å for the distal CC bond length, and a smaller value of 1.482(1) Å for the four lateral CC bonds that connect to the central carbon atom. The HCH angle is 113.7(13)°, and the HCH flap angle, defined as the angle of the HCH bisector and the distal CC bond, is 150.2(16)°. Corresponding r values are 1.122(2) Å, 1.560(3) Å, 1.485(1) Å, 115.1(13)°, and 148.9 (16)°. The results are in good accord with values from density functional calculations (B3LYP/cc-pVTZ) and resolve some questions about the structure reported in an earlier GED study, in particular about the HCH angle and anomalous rotational constants calculated for the structure.

Combined Electron-Diffraction, Spectroscopic, and Theoretical Determination of the Structure of N-Deuterio-trans-Methyldiazene, CH3N═ND. Conformational Effects of the N═N Double Bond

“…Reasonable values were obtained for the NN and CN distances, but the ND bond length and NND angle were not judged to be reliable and the work was not published. However, since that time a number of improvements in the analysis of GED data − and in the use of information from electronic structure calculations have occurred that have made possible the present reanalysis of this experiment. In particular, the experimental improvement involves the use of a flat-bed scanner instead of a rotating-plate densitometer in the radial averaging of the scattered intensity from the photographic plates used in the diffraction experiments.…”