Die Kristall- und Molekülstruktur vono-Fluorbenzoesäure

Abstract

o-Fluorobenzoic acid crystallizes in the monoclinic system, space group P21/c, with four molecules in a unit cell of dimensions a=6.71, b=3"81, c=25.05 A;/~=99"9 °.The detailed crystal structure was determined by normal and generalized electron-density projections along the a and b axes and three-dimensional parameter refinement. The calculations are based on 356 observed structure factors. The molecules occur as centrosymmetrical dimers with normal hydrogen bonds between adjacent carboxyl groups. The molecular structure of o-fluorobenzoic acid is overcrowded. The strain in a planar model for the molecule is relieved by a 21 ° twisting of the carboxyl group out of the plane of the aromatic ring, and by valency-angle distortions. The presence of hydrogen atoms including that in the hydrogen bond has been demonstrated. There is no intermolecular hydrogen bridge between the fluorine atom and the carboxyl group, but a strong van der Waals interaction can be assumed between the fluorine and the adjacent hydrogen atom.

Disordered Fluorine in 2-Fluorobiphenyl

“…(1995 (Received 7 November 1994;accepted 13 January 1995) Since the molecule lies across a twofold axis, the F atom on C2 must be disordered at 1:1 with the H atom on C2'. The bond-length distribution in the fluorosubstituted phenyl ring agrees well with the literature values (Krausse & Dunken, 1966;Young, Tollin & Sutherland, 1968;Sutherland & Rawas, 1983), but the C--F bond length [1.319 (4)/~] is significantly shorter. The biphenyl bond [C1---CI' 1.483 (4) A] is shorter than the value found in biphenyl (1.506/~).…”

On the magnetic behaviour of some hydrogen bonded molecules in crystals

“…In the crystalline state the o-halogenobenzoic acid molecules are completely associated forming dimers [25,26]. The carboxylic groups of the two molecules and the hydrogen bonds form an 8-membered ring linking the two molecules as shown in figure This can be regarded as a check of the accuracy of the measurements.…”

The crystal and molecular structure of B,B-bis-(p-fluorophenyl)boroxazolidine, (p-FC6H4)2BO(CH2)2NH2

“…This offers an explanation for the small differences between the B-C, B-O, C-N, C-O, and C(1)-C(2) bond lengths in this structure and those in (I), where the negative charges which occur at the fluorine atoms in this structure give rise to delocalization effects in the molecule. The mean C-F distance of 1.371 A is close to that of 1.368 A in o-fluorobenzoic acid (Krausse & Dunken, 1966) but significantly longer than the mean C(ar)-F distance of 1.328 .A in Tables of lnteratomic Distances and Configuration in Molecules and Ions (1965). The mean bond angles at tetrahedrally and trigonally coordinated atoms are 109.4 and 119.9 °.…”