Analyse structurale des dérivés fonctionnels des acides carboxyliques Partie III. Acétate d'éthyle, dérivés α-halogénés

Abstract

Methylene bending mode analysis of ethyl esters of acetic and haloacetic acids XCH 2CO 2C 2H 5 where X=H( I), F( II), Cl( III),Br ( IV) and I( V) reveals that in the dissolved state (CCl 4) these compounds have conformations induced by rotating motion of the XCH 2 and C 2H 5 groups (( II), ( III) and ( IV)) or by C 2H 5 group rotation exclusively (( I) and ( V)). In the last case, ( I) exists in gauche and anti conformations while ( V) occurs in gauche—gauche and gauche—anti conformations. A theoretical study of compounds ( I), ( II) and ( III) by the PCILO method and Onsager formalism leads to the following conclusion The conformers of ( I) have a dihedral angle (H 3)CC(H 2)OC of 70° (gauche conformer) and 180° (anti conformer). For ( II) and ( III), there are four stable conformers whose dihedral angle ϕ 3=(H 3)CC(H 2)OC and θ=XCCO values are in agreement with C 2H 5 and CH 2X group orientations found in experimental analysis.