Conjugated cycloropyls: the molecular structures and conformations of 1,1-dicyclopropylethene and dicyclopropyl ketone as studied by gas phase electron diffraction and ab initio calculations

摘要

The molecular structure and conformations of the two structurally related molecules 1,1-dicyclopropylethene and dicyclopropyl ketone have been studied experimentally by the gas electron diffraction method. For the former molecule a conformational mixture of 59(8)% gg (as 47% g~+g~+, and 11% g~+g~-) and 41% ga was observed, while the cyclopropyl rings of the ketone prefer a syn orientation (93(3)% syn syn; 7% syn atni). The syn oriented cyclopropyl groups of the ketone are substantially closer to the C=O bond that the gauche oriented cyclopropyls of the hydrocarbon are to the C=C bond (angle C~2-C~3-D: 121.3 deg vs. 127.2 deg). Results from ab initio MP2/6-31G~* optimization calculations are in excellent agreement with the observed ones.