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  • 1
    Electronic Resource
    Electronic Resource
    The effect of the azole ring on the conformational mobility of the dihydropyrimidine ring in 4,7-dihydroazolo[1,5-a]pyrimidines as judged from MNDO calculations (1994)
    Springer
    Russian chemical bulletin 43 (1994), S. 1343-1345 
    Details
    ISSN: 1573-9171
    Keywords: 4,7-dihydroazolopyrimidines ; MNDO method ; electronic structure ; conformational mobility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The equilibrium geometries of 4,7-dihydropyrazolo[1,5-a]pyrimidine, 4,7-dihydrotetrazolo [1,5-a]pyrimidine, 4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine, and 1,4-di-hydropyrimido [1,2-a]imidazole were calculated by the semiempirical quantum-chemical MNDO method. The dihydropyrimidine ring exhibits high conformational mobility in all of these compounds. The change in the energy occurring in the transition of the molecule to the boat conformation with an angle between the planar fragments of ±20° does not exceed 1 kcal mol−1. The mobility of the dihydro ring increases as interactions between the π-systems of the azole ring and the C=C double bond separated by an imino group and a methylene bridge decrease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00703690
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of substituents on the conformational mobility of the heterocycle in 1,4-dihydropyrimidine and its derivatives (1994)
    Springer
    Russian chemical bulletin 43 (1994), S. 1320-1323 
    Details
    ISSN: 1573-9171
    Keywords: 1,4-dihydropyrimidine ; 4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine ; conformational analysis ; molecular mechanics ; conformational mobility ; partially hydrogenated heterocycles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The equilibrium geometry of 1,4-dihydropyrimidine, 4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine, and their alkyl (Me, Et, Pri, But) and phenyl derivatives has been calculated by molecular mechanics method. The equilibrium conformation of unsubstituted molecules is planar, but it is easily transformed to the boat conformation with a small change in the conformational energy. The effect of substituents on the geometry and conformational mobility of the dihydropyrimidine ring has been studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00703685
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  • 3
    Electronic Resource
    Electronic Resource
    Conformational mobility of the six-membered ring in 5-oxo-1,3-cyclohexadiene and its derivatives (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 823-827 
    Details
    ISSN: 1573-9171
    Keywords: conformational analysis, molecular mechanics, MNDO method ; electronic structure ; conformational mobility ; 5-oxo-1,3-cyclohexadiene, alkyl, amino, and nitro derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular mechanics and MNDO calculations showed that the six-membered ring in the molecule of 5-oxo-1,3-cyclohexadiene possesses high conformational mobility. The transition from a planar equilibrium conformation to a distorted sofa conformation in which the C(sp2)-C(=O)-C(sp3)-C(sp2) torsion angle is equal to ±30° increases the energy of the molecule by less than 1 kcal mol−1. The influence of steric (R = Me, Et, Pri, But) and electronic (R = NH2, NO2) effects of substituents R on the equilibrium conformation and mobility of the carbocycle has been analyzed. Both types of substituents at unsaturated C atoms do not change the equlibrium conformation or flexibility of the six-membered ring. Substituents at saturated C atoms cause the transition of the carbocycle to the distorted sofa conformation and significantly restrict its mobility. The electronic structures of 5-oxo-1,3-cyclohexadiene and its amino and nitro derivatives have been analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696909
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