STRUCTURES OF PYRAZOLO[1,5-ALPHA]PYRIDINE DERIVATIVES

The pyrazolo[1,5-a]pyridine skeletons of 2-phenylpyrazolo [1 ,5-a]pyri dine-3-carbonitrile, C14H9N3 (2a), and S-2-methylthiopyrazolo [1,5-a]p yridin-3-yl p-chlorothiobenzoate, C15H11C1N2OS2 (2b), are planar [maxi mum deviation 0.019 (3) Angstrom for (2a) and 0.011 (5) Angstrom for ( 2b)]. The pyrazolo[1,5-a]pyridine skeleton of compound (2b), in which the 2- and 3-substituents are bonded to the pyrazole ring by two long C-S bonds, shows no significant distortion, while in (2a), with the 2- phenyl and the 3-cyano groups, considerable changes are seen in the bo nd angles resulting from the severe steric interaction accompanied by the resonance effect between the pyrazolo[1,5-a]pyridine and the pheny l group.