A theoretical study of the tautomerism and ionization of 5-substituted NH-tetrazoles

摘要: Abstract The energies, geometries and charge distributions of the five more stable forms (anion, 1H- 2H-neutral tautomers, 1,3-H,H+- 1,4-H,H+-cation tautomers) a series 5-R tetrazoles [R=H, CH3, C(CH3)3, Ph, Cl, CF3, NO2] in gas phase have been calculated with DFT/B3LYP method at 6-31G* level. For tetrazolate anions, shortening 1–2 bond simultaneous elongation 2–3 is observed when value σp constant substituent increases. A considerable ring aromaticity exhibited by also 2H-form neutral 1,3-H,H+-form cations it somewhat depends on nature substituent. values dipole moments 2H- 1H-forms correlate well constants substituents. relative thermodynamic stability 2H-forms as compared 1H-ones does not practically depend R. In contrast, case tetrazolium cations, most form 1,4-H,H+—for electron-donating substituents 1,3-H,H+—for electron-withdrawing ones. Good correlations between energies protonation anions experimental pKa pKBH+ values.