Ab initio study of the conformational and geometrical isomerism in heteroallyl and heteropropenyl systems

Conformational isomerism has been studied by ab initio methods (RHF/6-31+G*, MP2/6-31+G*) for CH2=CHCH2X heteroallyl and CH3CH=CHX heteropropenyl systems (X = H, Me, NMe2, OMe, PMe2, SMe, ONCH2). In 3-heteroprop-1-enes, substituents preferably occupy the AC position relative to the C=C double bond. The E isomers of 1-methylthio- and 1-methoxyprop-1-enes, which are thermodynamically more stable, have two stable forms, SP and AC; for 1-dimethylamino- and 1-imethylphosphinoprop-1-enes, the stable firms are AP and SC. The molecule of the E isomer of formoxime propenyl ether exists in two,forms, SC and AP, the latter being predominant. The Z isomers preferably exist in the form of AC (X = CH3O, CH3S) and AP (X = (CH3)(2)N, (CH3)(2)P, CH2=NO) conformations. Migration of the formoxime allyl ether, forming the E and Z isomers, is energetically double bond toward an heteroatom in favorable, the Z isomer being thermodynamically preferable.