Rotational isomerism in divinylether studied by gas phase electron diffraction, microwave spectroscopy, infrared band profile simulation and ab initio calculations

Abstract

The conformational behaviour of divinyl ether in the gas phase was explored by infrared band profile simulations and joint analysis of electron diffraction and microwave data. At 300 K the rotameric mixture contains 80% [ sp, ac] and 20% [ ap, ap] forms. Geometries have been studied using constraints taken from ab initio 4-21G gradient geometry and force field calculations. Differences between some unresolved bond distances and angles were constrained to the calculated values. Scale factors for the ab initio force field were refined from the diffraction data. In addition the transferability of scale factors from methyl vinyl ether to divinyl ether was tested. The investigation demonstrates that molecular orbital constrained models are consistent with and rationalize all experimental gas phase results. Subject to the ab initio constraints, the analysis yields the following model ( r g-distances, r α-angles; numbers in parentheses are 6 times the least-squares ESDs): (CH) = 1.103(12) A, (CC) = 1.337(2) A, (CO) = 1.389(2) A. Torsion angles for the [ sp, ac] form are −13(6)° and 145(4)°.