Structure and Reactivity of Pyrazoles

C-H and N-H bond-dissociation energies (BDEs) of pyrazole were calculated using composite ab initio CBS-Q, G3, and G3B3 methods (Table 3) 2003JP0883 . It was found that all these methods provided very similar BDEs, despite the fact that different geometries and different procedures in the extrapolation to complete incorporation of electron correlation and complete basis set limit were used. 

Bond CBS-Q G3 G3B3 recommended B3LYP Charge Spin Bond angle (°) 

Nuclear quadrupole resonance (NQR) frequencies were determined on the Cl isotope for several chloroindazoles and for two chloroindazole nucleosides at liquid nitrogen temperature 2000JMT(530)217 . The influence of the site of substitution and type of substituent on the resonance frequency was analyzed and the electron density distribution and electrostatic potential in the molecules were calculated by the B3LYP/6-31G(p) method and the results were correlated with experimental data. 

Ab initio calculations (STO-3G and 4-3IG) were carried out for methylpyrazoles-NH4 complexes 

Theoretical calculations at the ab initio level on simple trifluoromethylpyrazoles have been carried out 93JFC(63)271,93JST(29i)2ii as well as on cation (13) 87JOC4058 . Very high level computational calculations (up to MP4) have been carried out on the four tautomers of pyrazolinone (see Section 3.01.7.5.1) 93JA2352 . 

The conformation of V,V-linked biazoles, including l,l -bipyrazole, (14) has been calculated within the framework of the MNDO method the energy minimum for compound (14) is for a dihedral angle of 108° (N atoms in opposite positions) 84CJC687 . A similar study has been reported for a l-(2-pyridinyl)-l/f-pyrazole (24) derivative 93JHC865 . The complete potential surface of 

Both INDO and AM 1 calculations have been carried out on pyrazolidinones with special emphasis on the stability of their conjugated acids (protonation site) 9lBSB29l . 

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