CONFORMATIONAL ANALYSIS AND STRUCTURAL CHEMISTRY: A HYBRID APPROACH (ELECTRON DIFFRACTION).

摘要

A series of 6 {dollar}pi{dollar}-iso-electronically related compounds was studied by means of gas electron diffraction, supplemented with infrared, microwave and quantum chemical methods. Constraints from ab initio were used consistently and tested throughout this work. Rotational isomerism in the molecules was investigated by a perturbational approach, based on ab initio theory.; Electron diffraction showed methyl vinyl ether to occur solely in the sterically crowded syn (sp) conformation. The derived structure agreed with all available experimental data.; Divinyl ether is found to exist in a 80/20 mixture of (sp,ac) and (ap,ap) forms. In addition, IR profile simulations were included for the first time to select the conformers.; Methyl acetate was observed solely in the syn (sp) form. The comparison between our gas phase structure and the crystal structure was unexpectedly good.; Vinyl formate existed also in one rotamer, the (sp, ap) form and again IR profile simulations were conclusive about the rotamer mixture.; Although we are convinced that non-bonded interactions are indeed responsible for the occurrence of the conformations, the perturbational theory we tested did not lead to a satisfactory quantitative explanation.; The consistency of some distance corrections ({dollar}rsb g - rsb e{dollar}) in ab initio was confirmed.