Nuclear Quadrupole Resonance Study of Hydrogen Bonds in Solid 2-Methylbenzimidazole and 5,6-Dimethylbenzimidazole

Abstract

Substituted imidazole and benzimidazole often form polar hydrogen-bonded chains in the solid state. 2-Methylbenzimidazole is known to be a high-temperature organic ferroelectric. We have measured temperature dependences of 14 N nuclear quadrupole resonance (NQR) frequencies and proton T 1 in 2-methylbenzimidazole and 5,6-dimethylbenzimidazole. The NQR frequencies are assigned to amino and imino nitrogen positions. The NQR data exclude the possibility of proton two-site exchange in an N−H•••N hydrogen bond. The activation energies for the methyl group hindered rotation are determined in both compounds. The present 14 N NQR data are compared to the published 14 N NQR data in solid substituted and coordinated imidazoles, in substituted benzimidazoles and in imidazole in the gas phase. A linear correlation between the two inplane principal values of the quadrupole coupling tensor and the out-ofplane principal value of the quadrupole coupling tensor is observed in imidazole, ranging from the amino nitrogen position to the imino nitrogen position. Transition from the amino to the imino nitrogen position is determined on the correlation diagram. The correlation diagram can be used to quantitatively observe the asymmetry of the N−H•••N hydrogen bond. A similar correlation diagram is proposed also for substituted benzimidazoles. The magnitudes of the principal values of the 14 N quadrupole coupling tensor in ferroelectric 2-methylbenzimidazole show that the macroscopic ferroelectric ordering has in this compound a minor effect on the asymmetry of the N−H•••N hydrogen bonds.

14 N Nuclear Quadrupole Resonance Study of Polymorphism in Famotidine

“…Lines N g, N n −≥ N 3 : The spectra of the five‐membered imidazole ring compounds were studied in Refs. and . There, an empirical correlation for the imino nitrogen frequencies was found: …”

“…A tentative assignation was performed considering two criteria: Relative mutual similarity of the two chosen QFS‐s when passing from polymorph A to B and their resemblance to QFS‐s of known NQR spectra of other compounds with similar local molecular structure The correlation between the two pairs ν + /ν − of the two tentatively equivalent nitrogen sites of the polymorphs A and B, should agree with the same empirically affirmed ν + /ν − correlation, characteristic for many other molecules, containing the relevant structurally equivalent nitrogen surroundings (cf. Fig.…”

“…Empirical correlation between 14 N quadrupole frequencies < + versus < − in the environment of an amino group bound to a guanidine ion. 22 molecules, containing the relevant structurally equivalent nitrogen surroundings [16][17][18][19][20][21][22] (cf. Fig.…”

Synthesis and Antibacterial Activity of Some Derivatives of 2-Methylbenzimidazole Containing 1,3,4-Oxadiazole or 1,2,4-Triazole Heterocycle

“…Hence, it is surely melted at lower temperature. In contrast, compound 1 forms extramolecular hydrogen bonds as shown in the publication of Seliger andŽagar [20]. So, the melting point of compound 1 should be higher.…”

Crystal Structure, Raman Spectroscopy and Dielectric Properties of New Semiorganic Crystals Based on 2-Methylbenzimidazole

“…The only candidates for the role of charge carriers are the protons. Note that the proton conductivity has been observed in a large number of crystals with hydrogen bonds such as DBPI-DBP [23,58], MBI [59,62], etc.…”