A molecular balance to measure the strength of N-H center dot center dot center dot pi hydrogen bonds based on the tautomeric equilibria of C-benzylphenyl substituted NH-pyrazoles

作者：Cornago Pilar^*; Claramunt Rosa M; Bouissane Latifa; Elguero Jose

来源：Tetrahedron, 2008, 64(17): 3667-3673.

DOI：10.1016/j.tet.2008.02.026

• pyrazoles
• tautomerism
• B3LYP/6-3 1G** calculations
• hydrogen bonds

A theoretical (B3LYP/6-31G**) study of 30 pyrazoles, most of them existing in two tautomeric forms, has been carried out. 3(5)-(2-Benzyl phenyl)-5 (3)methyl-1H-pyrazole (11) and 3 (5)-(2-benzylbenzylphenyl)-5(3)-phenyl-1H-pyrazole (20) were synthesized from 2-benzoylacetophenone, and their annular tautomeric equilibrium determined. The substituent effects were statistically analyzed and discussed with the help of Hammett substituent constants. In the case of the 5-(2-benzylphenyl) groups, the strength of the N-H center dot center dot center dot pi hydrogen bond depends on the electronic effect of the substituent at position 3.

• 出版日期2008-4-21