EFFECTS OF CF2 GROUP PYRAMIDALIZATION IN THE 1,1,3,3-TETRAFLUOROPROPENYL ANION

Ab initio calculations with the 6–31G* basis set were carried out on planar and pyramidalized geometries of the 1,1,3,3‐tetrafluoropropenyl anion and on two geometries with one CF2 group rotated out of conjugation. Structures with at least one pyramidalized CF2 group are substantially lower in energy than the corresponding unpyramidalized structures for both rotated and unrotated geometries. At the MP2/6–31G* level of theory, three structures of approximately equal energy all lie 17–18 kcal mol−1 below the planar C2v structure. These include a Cs geometry with one CF2 group rotated out of conjugation, an unrotated C1 structure with unequal CC bond lengths and an unrotated, pyramidalized C2 structure with equal CC bond lengths. Copyright © 1990 John Wiley & Sons Ltd.