Study of Hindered Internal Rotation in Some N-vinyl Substituted Amides by Nuclear Magnetic Resonance Spectroscopy PDF Download
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Author: Douglas George Gehring
Publisher:
ISBN:
Category : Amides
Languages : en
Pages : 94
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Author: Douglas George Gehring
Publisher:
ISBN:
Category : Amides
Languages : en
Pages : 94
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Author: James Calvin Woodbrey
Publisher:
ISBN:
Category : Amides
Languages : en
Pages : 420
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Author: William Chung-Tsing Tung
Publisher:
ISBN:
Category : Amides
Languages : en
Pages : 468
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Author: Lester Reinhardt Isbrandt
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ISBN:
Category : Amides
Languages : en
Pages : 292
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Author: William Chung-Tsing Tung
Publisher:
ISBN:
Category :
Languages : en
Pages : 211
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Author: Daniel S. Dyer
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Category :
Languages : en
Pages : 70
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The temperature and solvent dependence of the nuclear magnetic resonance (nmr) spectra of a number of amides has been studied. Hindered internal rotation about the C(O)-N and aryl-nitrogen bonds was detected in a series of N-acylhydrazobenzenes. In this series of compounds, hindered rotation about the C(O)-N bond afforded, in most cases, a mixture of cis-trans isomers in solution. These isomers were easily detected by nmr spectroscopy. Thus the free energies of activation, at the coalescence temperatures, for the hindered rotations were calculated. Similar temperature dependence studies on the nmr spectra of N-phenylacetamide and N-(o-tolyl) acetamide also afforded evidence for hindered internal rotation about the C(O)-N bond. However for these compounds, one isomer predominated to such a degree in solution that the presence of the second isomer was barely detected by nmr spectroscopy. A temperature dependence study of the fluorine-19 resonance spectra of both 1 and 2 deg rotation about the C(O)-N bond. However for the first time, coupling between the trifluoromethyl group and a nitrogen proton was observed. Also the proton nmr spectrum of 1,1,1-trifluoroacetamide, itself, in a dry acetone solution at low temperatures afforded the direct observation of two separate signals for the two nitrogen protons. (Author).
Author: Erick L. May
Publisher:
ISBN:
Category :
Languages : en
Pages : 35
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Author: A. G. Whittaker
Publisher:
ISBN:
Category :
Languages : en
Pages : 37
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The temperature dependence of the chemical shifts due to hindered internal rotation was measured for diethylformamide, diethylacetamide, diisopropylformamide, diisopropylacetamide and for solutions of these molecules in various solvents. In all cases, the chemical shifts showed unusual behavior. Conventional methods coupled with certain approximations were used to calculate activation energies as estimates for the rotational barrier to the internal rotation about the N-CO bond. These values were found to lie in the range of 5 to 26 kcal/mole. However, it is difficult to determine the real significance of these numbers; the behavior of the chemical shifts was such that no underlying concepts could be developed that would correlate the observed results except for the conclusion that the solvent plays a dominant role in the relationship between chemical shift and temperature. (Author).
Author: Zon-son Chang
Publisher:
ISBN:
Category :
Languages : en
Pages : 57
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Author: Laurine Anna LaPlanche
Publisher:
ISBN:
Category : Amides
Languages : en
Pages : 318
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