Divalent N(I) Character in 2‑(Thiazol-2-yl)guanidine: An Electronic Structure Analysis

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2012-09, Vol.116 (36), p.9071-9079
• Main Authors: Bhatia, Sonam, Bagul, Chandrakant, Kasetti, Yoganjaneyulu, Patel, Dhilon S, Bharatam, Prasad V
• Format: Article
• Language: English
• Subjects: Computer Simulation; Electronic structure; Electrons; Guanidines - chemistry; Mathematical models; Models, Molecular; Nitrogen - chemistry; Physical chemistry; Protonation; Quantum chemistry; Spectroscopy; Thiazoles - chemistry; Valence
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp304789u

Several medicinally important compounds carry a 2-(thiazol-2-yl)guanidine unit. These species are generally (erroneously) represented as 1-(thiazol-2-yl)guanidine species. Quantum chemical studies were performed to identify the appropriate tautomeric state of this class of compounds. B3LYP/6-31+G(d) calculations indicate the preferred tautomeric state of these species is associated with the 2-(thiazol-2-yl)guanidine structure rather than the 1-(thiazol-2-yl)guanidine structure. G2MP2 calculations on the model system were carried out to study the electronic structure, electron delocalization, and protonation energy; MESP, ELF, HOMA, AIM, and NBO analyses were also carried out. The results indicate that this class of compounds may be treated as species with hidden ::N(←L)R character. Upon protonation of the thiazole ring nitrogen, these systems show the electronic structure as in ::N(←L)2 ⊕ systems with divalent N(I) oxidation state.