The structure of 11,11-difluoro-1,6-methano[l0]annulene

Abstract

The crystal and molecular structure of 11,11-difluoro-l,6-methano[10]annulene has been determined and refined by least-squares methods. The crystals are orthorhombic, space group Pna2a, with a = 9-233, b= 13"235, c=7"055 A and four molecules per unit cell. Intensity data were collected visually from Weissenberg photographs. The solution of the phase problem was readily obtained by finding the orientation of a plausible molecular model with respect to the crystallographic axes through a systematic search of the Patterson synthesis around the origin; the position of the molecule in the unit cell was then found by molecular packing energy calculations. After refinement by least-squares, the final R index is 0.080. The presence of fluorine atoms does not seem to affect the conformation of 1,6-methano [10]annulene; the distance C(1)-C(6) is 2.25 A,, excluding any 'double norcaradiene' character for this compound, in agreement with chemical and spectroscopic evidence.

The influence of substituents on the equilibrium bisnorcaradiene–[10]annulene. The crystal and molecular structure of 11,11-dimethyltricyclo[4,4,1,01,6]undeca-2,4,7,9-tetraene

“…The structure determination of 1,6-methano [10]annulene-2-carboxylic acid (Ia) (Dobler & Dunitz, 1965), and of l l,ll-difluoro-l,6-methano [10]annulene (lb) (Gramaccioli & Simonetta, 1971) confirmed the presence of an aromatic perimeter ring, in agreement with chemical and spectroscopic (n.m.r.) results.…”

“…The central distance C(1)-C(6) becomes 2. 25 A in 11,11-difluoro-l,6-methano[10]annulenq (Ib) (Gramaccioli & Simonetta, 1971), and 2-257 A in 1,6-methano[ 10]-annulene-2-carboxylic acid (Ia) (Dobler & Dunitz, 1965), thus corresponding to a nonbonded separation. The possibility of the presence of both annuleneand bisnorcaradiene-type molecules in the crystals of DIM* is in contrast with the quite 'normal' features of thermal parameters (see Fig.…”

“…As part of a programme of study on the molecular geometry of systems with 4n + 2 n-electrons (n greater than 1) (Gavezzotti, Mugnoli, Raimondi & Simonetta, 1972;Gramaccioli, Mugnoli, Pilati, Raimondi & Simonetta, 1972;Gramaccioli & Simonetta, 1971;Gramaccioli, Mimun, Mugnoli & Simonetta, 1971), an interesting problem arose in comparing structural results for two 'similar' types of compounds, (I) and (II), for which chemical and spectroscopic data suggested quite different configurations (Vogel, 1969). The structure determination of 1,6-methano [10]annulene-2-carboxylic acid (Ia) (Dobler & Dunitz, 1965), and of l l,ll-difluoro-l,6-methano [10]annulene (lb) (Gramaccioli & Simonetta, 1971) confirmed the presence of an aromatic perimeter ring, in agreement with chemical and spectroscopic (n.m.r.)…”

The structure of bicyclo[2,2,1]hept-5-ene-2,3-exo-dicarboxylic anhydride

“…Programs written in this laboratory in the Fortran IV language for orthorhombic, monoclinic and triclinic crystals Bianchi, 1972) have been successfully applied to the solution of other structures (Gavezzotti, Mugnoli, Raimondi & Simonetta, 1972;Gramaccioli & Simonetta, 1971;Bianchi, Mugnoli & Simonetta, 1972). The method is essentially close to the procedure adopted by Nordman (1966): the sharpened Patterson function (not necessarily on an absolute scale or with manipulations at the origin), evaluated at intervals of about 0.1 ~ along the three crystallographic axes, is considered for this purpose only within 3.2 ~ from the origin (this excludes all intermolecular vectors) and stored in the memory of the !computer.…”

A discussion on constrained refinements

“…The structure of 11,11-difluoro-1,6-methano[ 10]-annulene (DIF) was determined at room temperature (Gramaccioli & Simonetta, 1971)and at 173 K (Pilati & Simonetta, 1976 Crystal data at 173 K were a = 9.111 (1), b = 13.203 (2), c = 6.981 (1) /k, Z = 4; orthorhombic, space group Pna2 r The molecular geometry obtained by analysis of room-temperature data shows an unexpected distortion from free-state molecular symmetry. The molecular model derived from X-ray data collected at low temperature is near to C 2 symmetry: all the differences from C 2 symmetry are within three times the standard deviation, except for the angles C(6)-C(I1)-F(1), 114.0 (2) ° and the C2 symmetry related C(1)-C(11)-F(2), 113.0 (2)°; the discrepancy from mm2 symmetry is more marked.…”