The Rotational Zeeman Effect of Pyrazole and Imidazole

Abstract

The rotational Zeeman effect of the most abundant isotopic species of pyrazole and of imidazole has been studied under ΔM= 0 and ΔM=±1 selection rules. With field close to 1.9 Tesla, the nuclear Zeeman effect uncouples the rotational angular momentum and the spins of the two nonequivalent l4N quadrupole nuclei. The observed g-tensor elements are gaa = − 0.07498(14), Obb = −0.12531(13), and gcc = 0.06346(12) for pyrazole and gaa = −0.09339(16), gbb = −0.10444(14), and gcc = 0.06051(15) for imidazole. The values for the magnetic susceptibility anisotropics in units of 10−6 erg/(G2 mol) are 2xaa− Xbb−Xcc = 39.53(24) and 2xbb−xcc− Xaa = 51.20(21) for pyrazole and 2xaa − Xbb − Xcc = 45.76(31) and 2xbb − Xcc − Xaa = 42.19(41) for imidazole. (Given uncertainties are single standard deviations of the fit.) The so-called nonlocal (π-ring current) contributions to the out of plane components of the susceptibility tensor, [FORMULA OMITTED], derived as differences between the observed susceptibilities and values calculated from additivity rules for local atom susceptibilities, are compared to those derived earlier for other aromatic five membered ring molecules. © 1987, Walter de Gruyter. All rights reserved.