The Crystal and Molecular Structure of 8, 8-Dicyanoheptafulvene

Abstract

Crystals of 8, 8-dicyanoheptafulvene, C10H6N2, are monoclinic, with two molecules in a unit cell with the dimensions a=7.84, b=13.14, c=3.99 Å, and β=97.9°; the space group is P21⁄m. The intensities were recorded on multiple-film equi-inclination Weissenberg photographs and measured visually against a standard scale. A trial structure was constructed from the Patterson projections, P(u, v) and P(u, w), and a Harker section, P(u, 1/2, w). The atomic coordinates and anisotropic temperature factors were refined by the least-squares method. The final R factor for (hkl) reflections is 0.107. A considerable bond alternation in the conjugated seven-membered ring has been observed. The average long and short bond lengths in the ring are 1.44 and 1.34 Å respectively. The shortest C=C bond measures 1.31 Å, which is shorter than that in ethylene. The exocyclic C=C bond length is 1.42 Å, suggesting a considerable dipolar resonance structure, one which may be responsible for the stability of the compound. The C≡N bond length is 1.13 Å. The molecule deviates slightly from being planar; it lies nearly parallel to the (101) plane. All the intermolecular separations correspond to normal van der Waals interactions; the perpendicular distance between the molecular planes is 3.4Å. The thermal motion was interpreted in terms of rigid body vibrations, and the bond lengths and angles were corrected for the rotational oscillations.

20-Dicyanomethylene-5,8,11,14-tetraoxa-2,17-dithiabicyclo[16.4.1]tricosa-1(23),18,21-triene and its mercury(II) dichloride complex

“…The exocyclic C C bond length [C1ÐC8 1.397 (3) A Ê ] of (I) is similar to those [1.389 (3) and 1.392 (5) A Ê ] of 5-and 7-(dicyanomethylene)-2,3-dihydrocyclohepta-1,4-dithianes (Kubo et al, 1994) and is shorter than that [1.422 (13) A Ê ] of 8,8-dicyanoheptafulvene (Shimanouchi et al, 1966).…”

Heptafulvalene: ring strain or hydrogen repulsion?

“…In heptafulvalene the angle opposite the exocyclic double bond (117"5 °) is much smaller than this value. As was noted by Bartell (1960) in an electron diffraction study of isobutylene, the CCC angles opposite C=C bonds are generally smaller than 120 °, There is a good correlatioD Thomas & Coppens (1972) Shimanouchi, Ashida, Sasada & Kakudo (1966 between the C=C bond length and the CCC angle. Some experimental data summarized in Table 1 show that heptafulvalene is no exception in this respect.…”

5- and 7-dicyanomethylene-1,2-ethylenedithiocycloheptatrienes

“…The exocyclic double bond of 8,8-dicyanoheptafulvene (3) has single-bond character (1.422A) (Shimanouchi et al, 1966), whereas that of 3,4-diacetoxy-8,8-dimethylheptafulvene has typical double-bond character (1.343 A) (Yin, Mori, Takeshita & Inoue, 1991). Electron-withdrawing groups at C(8) enhance the contribution of the cycloheptatrienylium cation to the structure of heptafulvenes, and thus have a stabilizing effect.…”

“…(Shimanouchi et al, 1966;Yin et al, 1991). The exocyclic ~C bond lengths of (1) and (2) (2) showing the atomic numbering scheme.…”