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

Abstract

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 anti). The syn oriented cyclopropyl groups of the ketone are substantially closer to the CO bond than the gauche oriented cyclopropyls of the hydrocarbon are to the CC bond (∠C2–C3–D: 121.3° vs. 127.2°). Results from ab initio MP2/6-31G* optimization calculations are in excellent agreement with the observed ones.