The trifluoroacetato (CF3COO–) and trifluoroacetate (CF3COO–) groups, their conformation from a database survey of crystal structures and ab initio MO calculations

Abstract

Data for structures involving either of these groups have been drawn from the Cambridge Structural Database and divided into bidentate and monodentate categories. Statistical distributions of bond distances, selected bond and torsion angles from 414 groups contained in 194 structures yield the following mean values (with e.s.d.'s) : C-F = 1.29 (6), C-C = 1.53 (4), C-O (bidentate)= 1.24 (5), C-O- (monodentate) = 1.25 (4), C=O (monodentate)= 1.21(4) A. Angles in the CF group vary widely from the expected threefold symmetry (e.s.d. of distribution 8.8°). Torsion angles F-C-C-O for the bidentate groups range fairly evenly over all possible values, suggesting free internal rotation. Among monodentate groups all values of the torsional angles are possible but with a marked preference for a C-F to eclipse the carbonyl C=O bond. These observations show good agreement with the results of ab initio calculations using GAUSSIAN90. The calculated barrier to rotation for the bidentate (ion) form of the group is only 310 Jmol- 1 and for the monodentate form (as in the acid) 2.55 kJmol- 1 .