caa a22 4500 469072288 CHVBK 20180323132925.0 cr unu---uuuuu 170328e19920801xx s 000 0 eng 10.1007/BF00672790 doi (NATIONALLICENCE)springer-10.1007/BF00672790 A semiempirical and ab initio MO study of the tautomers of N -unsubstituted pyrazolones [hydroxy pyrazoles] [Elektronische Daten] [Venelin Enchev, Georgi Neykov] Semiempirical (MNDOC, MINDO/3, AM1, and MNDO) and ab initio (STO-3G and 4-31G basis sets) calculations on the relative stabilities, structures, and dipole moments of the 8 theoretically possible tautomeric forms of pyrazolone are reported. It is shown that MNDO + CI and MINDO/3 predict that 5-hydroxy pyrazole, 3-hydroxy pyrazole, and 2-pyrazolin-5-on are the most stable. These results correspond to the known experimental data. Of all used quantum chemical methods, the MINDO/3 results for the dipole moments of the investigated tautomers are in best agreement with the known experimental data. The electronic excitation energies were calculated using the CNDO/S-CI method. The results are in good agreement with the experimental UV spectra. Plenum Publishing Corporation, 1992 Enchev Venelin Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria aut Neykov Georgi Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria aut Structural Chemistry Kluwer Academic Publishers-Plenum Publishers 3/4(1992-08-01), 231-238 1040-0400 3:4<231 1992 3 11224 https://doi.org/10.1007/BF00672790 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00672790 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Enchev Venelin Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria aut NATIONALLICENCE 700 1- Neykov Georgi Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria aut NATIONALLICENCE 773 0- Structural Chemistry Kluwer Academic Publishers-Plenum Publishers 3/4(1992-08-01), 231-238 1040-0400 3:4<231 1992 3 11224 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer