On the nature of the CH··FC hydrogen bond in 2,3-dichloro-5,5-dicarbonitrile-6,6-bis(trifluoromethyl)-bicyclo[2.2.1]heptane

Abstract

In the title molecule two unusual hydrogen bonds (HB) exist (as determined by X-ray analysis [A.N. Chekhlov, V.I. Fetisov, et al., Dokl. AN SSSR, 297 (1987) 1177]). This HB pattern led us to propose the existance in this molecule of two pseudolactonic rings (CF 2 approximating to a CO group). This assumption allows comparison of such molecules with other ‘cage’ convulsants such as picrotoxinin. Thus, the nature of such HB must be understood for further understanding of the structure-activity relationships. Structure of molecule ▪ Interatomic X-Ray MMX distance (Å) I (C7)H ··F(CF 2) 2.30 2.26 II (C2)H ··F(CF 2) 2.16 2.23 sum of the van-der Waals radii: H ··F 2.55–2.67 In this work the empirical method of molecular mechanics calculations MMX (N. Allinger, PCMODEL program was used). The force field in this protocol contains no parameters for the HB's mentioned above; such HB (if it occurs) must be viewed as a short obligate van der Waals contact. The results obtained support this idea: the MMX-optimized geometry parameters are very similar to those determined by X-ray analysis. The observed HB is generated because of barriers to internal rotations of the CF 3-groups: I 55.4; II 28.2 kcal/mole (numeration see Table and Fig.; rigid rotor approximation).