The substituted norcaradiene, CllH10N2, crystallizes in the orthorhombic space group P212121 with four molecules in a cell having a= 11.044, b = 7.126, c= 12.113 A. Copper K~ diffraction data measured by scintillation counter gave an R of 3.9 % when fit by least squares to a model including a bonds. The molecule has nearly exact Cs symmetry; the cyclopropane ring is inclined at about 73 ° to the approximately planar C6 ring. Bonds adjacent to the C3 ring are shortened by 0-02-0.03 A from corresponding unstrained values; cyclopropane C-C bonds are 1.558, 1.553, and 1.500 A. The experimental electron density is matched much better by a 'bent' bond cyclopropane model than the straight-bond model; the angle of bending is roughly 20 ° .
IntroductionCyclopropane rings present opportunities to study carbon in unusual hybridization states for which little accurate geometrical information is available. The present study was undertaken with the additional purpose of * Contribution No. 1071. t Present address: Department of Chemistry, Tulane University, New Orleans, La., U.S.A.confirming the bicyclic nature of the material CnH10Nz, one of the simplest containing the norcaradiene skeleton (Ciganek, 1965).
Experimental dataClear, block-like crystals of C11H1oN2, 2,5-dimethyl-7,7-dicyanonorcaradiene, and of C9H6N2, 7,7-dicyanonorcaradiene, were supplied by Dr Ciganek. On Cu 28 STRUCTURE OF 2,5-DIMETHYL-7,7-DICYANONORCARADIENE Kc~Weissenberg and Mo Kct precession photographs both showed reciprocal lattice extinctions characteristic of space group P212121 (D4). The unit-cell constants of C9H6N2 were determined from Cu Kc~ rotation and Weissenberg photographs to be a= 11.07 + 0.05, b=5.76+0.02, c=12.16+0.05 A. The dimethyl compound had a somewhat more equidimensional habit and was chosen for a complete study. A zero layer [100] Weissenberg photograph made in a special lattice-constant camera (Fritchie, 1966a) with Cu Kc~ radiation gave b=7.126 + 0.001, c= 12.113 + 0.001 A. The a-axis dimension of 11.044+0.002 A was measured on a Picker goniometer with Cu Kc~ radiation. Wavelengths used in the calculations were 1.54050 and 1.54434 A for Cu K~I and Cu K~2. Calculated densities are 1.213 g.cm -3 and 1.186 g.cm -3 for C9H6N 2 and CHHIoN2, respectively, assuming four molecules per cell in each case.A polyhedral specimen about 0.4 mm in diameter was chosen for intensity collection. The crystal was found to sublime rather rapidly; after collection of the hOl, Okl, and hkO data the crystal was coated with a layer of Krylon acrylic ester resin about 0.05 mm thick. This plastic was essentially amorphous and completely halted the sublimation without excessively increasing the background. All intensity data were collected with a Picker scintillation counter, using a pulse-height discriminator symmetrically set to collect about 9070 of the Cu Ka pulse distribution. The generator was linevoltage stabilized; more serious intensity variation caused by crystal sublimation was eliminated by measurement of one or two standard reflections about e...