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  • 1
    Electronic Resource
    Electronic Resource
    Cycle inversion in 1,3-cyclohexadiene and its 5-alkyl derivatives (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 1100-1102 
    Details
    ISSN: 1573-9171
    Keywords: 1,3-cyclohexadiene ; 5-alkyl-1,3-cyclohexadienes ; molecular mechanics ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Cycle inversion in 1,3-cyclohexadiene and its 5-alkyl derivatives is studied by means of the MMP2 molecular mechanics procedure. The choice of a torsion angle between single bonds as a reaction coordinate is justified. Substituents at the C(5) atom (R=Me, Et,i-Pr,t-Bu) are shown to have little effect on the cycle shape, and the equatorial conformer is preferable to the axial one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00704208
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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
    Effect of electronic interactions between double bonds on the conformational flexibility of 1,4-cyclohexadiene (1994)
    Springer
    Russian chemical bulletin 43 (1994), S. 1587-1588 
    Details
    ISSN: 1573-9171
    Keywords: conformational analysis ; 1,4-cyclohexadiene, conformational flexibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electronic structure of 1,4-cyclohexadiene for various angles between the double bond planes has been calculated by the AM1 method. The effects of through-bond and through-space interactions, which result in flattening and unflattening, respectively, are oppositely directed. These effects are specified for various bending angles. In addition to steric factors, electronic factors affect the conformational flexibility of 1,4-cyclohexadiene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00697157
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular structure and conformational analysis of chirai (−)-3-(4-bromobenzylidene)-1-isopropyl-2-methoxy-4-methylcyclohexene (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 2331-2336 
    Details
    ISSN: 1573-9171
    Keywords: molecular structure ; conformational analysis ; crystal structure ; X-ray structural analysis ; molecular mechanics ; (−)-3-(4-bromobenzylidene)-l-isopropyl-2-methoxy-4-methylcyclohexene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract (−)-3-(4-Bromobenzylidene)-1-isopropyl-2-methoxy-4-methylcyclohexene, capable of inducing spiral supramolecular ordering when introduced to nematic and some smectic mesophases, has been studied by an X-ray structural analysis. The crystals are orthorhombic; at 20 °Ca = 6.055(1),b = 13.282(3),c=20.734(4) Å,V=1668(1) Å3,d calc = 1.380 g cm−3, space groupP2 12121 Z=4. The cyclohexene ring has a conformation intermediate between a sofa and a half-chair. The methyl and methoxyl groups are in asyn orientation with respect to the mean plane of the cycle. The angle between the plane of the aryl substituent and the exocyclic double bond is 33°. The observed distortions of bond angles at unsaturated carbon atoms are typical of derivatives of benzylidenecyclohexene. Molecular mechanics calculations demonstrated that the conformation observed in the crystalline state is not the most favorable, and this conformation is stabilized through intermolecular interactions upon stacking in crystals. It was shown that the relative orientation of the methyl and methoxyl groups as well as the orientation of the aryl substituent substantially affect the conformation of the cyclohexene ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713603
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational analysis of 5,6-dihydropyrimidine and its derivatives (1995)
    Springer
    Russian chemical bulletin 44 (1995), S. 470-474 
    Details
    ISSN: 1573-9171
    Keywords: conformational analysis ; molecular mechanics ; dihydropyrimidines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The equilibrium geometry and inversion barriers of 5,6-dihydropyrimidine, 6,7-dihydroazolopyrimidines with node nitrogen atoms and their alkyl (Me, Et, Pri, But) and phenyl derivatives were calculated using a molecular mechanics approach. Annelation with azole cycles and the introduction of substituents have a slight effect on the equilibrium conformation of the dihydrocycle (distorted sofa). Alkyl substutuents at saturated carbons have an essentially equatorial orientation in 5,6-dihydropyridimine derivatives and are axial in the annelated analogs. On the other hand, the equatorial conformers are more stable in phenyl derivatives of dihydroazolopyrimidines. Factors determining the relative stability of conformers were analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00702390
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  • 6
    Electronic Resource
    Electronic Resource
    Conformational flexibility of six-membered 1,2-dihydrocycles based on the results of AM1 calculations (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 2509-2511 
    Details
    ISSN: 1573-9171
    Keywords: 1,3-cyclohexadiene ; 2H-pyran ; 2H-thiopyran ; 1,2-dihydropyridine ; oxo ; imino ; methylene derivatives ; conformational analysis ; conformational flexibility ; AM1 method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformational flexibility of 2H-pyran, 1,2-dihydropyridine, 2H-thiopyran, their oxo, imino, and methylene derivatives, and the 5-oxo, imino, and methylene derivatives of 1,3-cyclohexadiene was studied by the semiempirical quantum-chemical AM1 method. All compounds have planar equilibrium conformations and similar electronic structures. The transition to a distorted sofa conformation with the =C-X-C(=Y)-C= torsion angle (X = CH2, NH, O, or S; Y = H2, O, NH, or CH2) of ±20° increases the energy of the molecule by less than 1.5 kcal mol−1. The reasons for the high conformational flexibility of these dihydrocycles were analyzed. The nonaromatic character of the cyclic π-system is the factor that determines the conformational flexibility of the dihydrocycle in ylide derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01431105
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  • 7
    Electronic Resource
    Electronic Resource
    Electronic structure and conformational flexibility of 1,2-dihydropyridine, 1,2- and 1,6-dihydropyrimidines, and their ylide derivatives (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 1833-1835 
    Details
    ISSN: 1573-9171
    Keywords: 1,2-dihydropyridine ; 1,2-dihydropyrimidine ; 1,6-dihydropyrimidine ; ylide derivatives ; AM1 method ; electronic structure ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Molecular and electronic structures of 1,2-dihydropyridine, 1,2- and 1,6-dihydropyrimidine, and their oxo, imino, and methylene derivatives were studied by the semiempirical quantum-chemical AM1 method. In all compounds, the heterocycle exhibits a high conformational flexibility. The transition from a planar equilibrium conformation to a distorted sofa conformation with the =C-NH-C-C(N)= torsion angle of ±20° causes an increase in the energy by less than 1.7 kcal mol−1. All molecules have similar π-electronic structures, which, apparently, determines the similarity in their conformational behavior. The bending strain and the nonaromatic character of the cyclic π-system are the factors that stabilize the nonplanar conformation of the ring in unsubstituted dihydroazines and ylide derivatives, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01457758
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  • 8
    Electronic Resource
    Electronic Resource
    Conformational analysis ofortho-substituted diphenyl ethers and diphenylmethanes with linear substituents (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 2733-2736 
    Details
    ISSN: 1573-9171
    Keywords: ortho-substituted diphenylmethanes and diphenyl ethers ; conformational analysis ; molecular mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Conformational analysis of di-ortho-substituted diphenylmethanes and Biphenyl ethers containing I, CCH, and CCCCH substituents was carried out by the molecular mechanics method using the MM3 program. Several minima on the potential energy surface, which correspond to thegg, gt, tg, andort conformations, were found. An increase in the length of the linear substituent results in a substantial decrease in the difference in the relative energies of conformers. Barriers to conformational transitions between thegt, tg, andort conformers are less than 2 kcal mol−1. The transitionort-gg requires expenditure of energy of up to 5 kcal mol−1. Two valleys of centrosymmetric pairs of thegt, tg, andort conformers are separated by a barrier of up to 6 kcal mol−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01430631
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  • 9
    Electronic Resource
    Electronic Resource
    Electronic structure and conformational flexibility of 1,4-dihydroazines and their 4-ylide derivatives (1996)
    Springer
    Russian chemical bulletin 45 (1996), S. 1836-1839 
    Details
    ISSN: 1573-9171
    Keywords: 1,4-dihydroazines ; ylide derivatives ; conformational analysis ; conformational flexibility ; semiempirical quantum-chemical AM1 method ; electronic structure ; aromaticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformational flexibility of 1,4-dihydropyridine, 1,4-dihydropyrimidine, 1,4-dihydropyridazine, 1,4-dihydro-1,3,5-triazine, and their 4-oxo, imino, and methylene derivatives was studied by the semiempirical quantum-chemical AM1 method. It was demonstrated that the replacement of the methylene group in the dihydroazine ring by the exocyclic double bond results only in an increase in the rigidity of the heterocycle rather than leading to a loss of its conformational flexibility. It was suggested that nonplanar conformations of rings in ylide derivatives are stabilized by the nonaromatic cyclic π-system. Introduction of the exocyclic double bond does not cause a substantial change in the π-electronic structure of the heterocycle. The aromaticity indicesI 6 andI 6(π) were calculated. The correlation between these indices and a change in the energy upon bending of the heterocycle was established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01457759
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  • 10
    Electronic Resource
    Electronic Resource
    Cycle mobility in 1,4-dihydropyridine and its monoalkyl and phenyl derivatives (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 1160-1162 
    Details
    ISSN: 1573-9171
    Keywords: 1,4-dihydropyridine ; molecular mechanics ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The conformational mobility of the 1,4-dihydropyridine cycle has been studied by the molecular mechanics method. It was shown that the N(1) and C(4) atoms are displaced asymmetrically from the plane of the double bonds. The asymmetry is the result of conjugation between the nitrogen lone pair and the π systems of the double bonds. The influence of alkyl and phenyl substituents at the carbon atoms on the equilibrium conformation and cycle mobility has been investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00701996
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