Combined Utilization of 1H NMR, IR, and Theoretical Calculations To Elucidate the Conformational Preferences of Some l-Histidine Derivatives

2017 ◽  
Vol 121 (3) ◽  
pp. 729-740 ◽  
Author(s):  
Carolyne B. Braga ◽  
Roberto Rittner
Keyword(s):  
1H Nmr ◽  
Theoretical Calculations ◽  
Conformational Preferences ◽  
Histidine Derivatives

Proximity effects in 29Si, 13C, and 1H NMR spectra of ortho substituted phenoxytrimethylsilanes

1990 ◽  
Vol 55 (8) ◽  
pp. 2019-2026 ◽  
Author(s):  
Jan Schraml ◽  
Václav Chvalovský ◽  
Harald Jancke ◽  
Peter Koehler ◽  
Mikhail F. Larin ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
1H Nmr ◽  
Proximity Effect ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Proximity Effects ◽  
1H Nmr Spectra ◽  
Methyl Groups ◽  
Conformational Preferences

NMR Spectra of eight ortho substituted phenoxytrimethylsilanes, 2-X-C6H4-OSi(CH3)3 (X = Cl, Br, OCH3, NH2, NO2, OSi(CH3)3, CH3, and H), are reported. In contrast to analogous ortho substituted methoxybenzenes the 13C chemical shifts of C-2 and C-6 aromatic carbons do not exhibit consistent trends indicating different conformational preferences in the trimethylsiloxybenzenes. Under the influence of the ortho substituents the nuclei of OSi(CH3)3 group (29Si, 13C, and 1H) are deshielded; compounds with X = CH3 (and H) appear anomalous in this respect. It is argued that this proximity effect is not due to an interaction involving terminal methyl groups but involves the oxygen atom of the OSi(CH3)3 group; it is most likely due to an interaction with unshared electrons of the ortho substituent.

Conformational preferences of N-acetyl-N′-methylprolineamide in different media: a 1H NMR and theoretical investigation

2019 ◽  
Vol 43 (4) ◽  
pp. 1757-1763 ◽  
Author(s):  
Carolyne B. Braga ◽  
Weslley G. D. P. Silva ◽  
Roberto Rittner
Keyword(s):  
1H Nmr ◽  
Theoretical Investigation ◽  
Conformational Preferences ◽  
Non Covalent Interactions ◽  
Covalent Interactions

The conformational preferences and role of non-covalent interactions on the geometries of Ac–Pro–NHMe were elucidated in isolated phase and solution.

Synthesis of 4-Aryl-3(5)-(2-hydroxyphenyl)pyrazoles by Reaction of Isoflavones and their 4-Thio Analogues with Hydrazine Derivatives

2007 ◽  
Vol 60 (12) ◽  
pp. 905 ◽  
Author(s):  
Albert Lévai ◽  
Artur M. S. Silva ◽  
José A. S. Cavaleiro ◽  
José Elguero ◽  
Ibon Alkorta ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Nmr Spectroscopy ◽  
Hydrogen Bonds ◽  
Hydrazine Hydrate ◽  
1H Nmr ◽  
Theoretical Calculations ◽  
Intramolecular Hydrogen Bonds ◽  
Nmr Study ◽  
Intramolecular Hydrogen ◽  
New Compounds

4-Aryl-3(5)-2-(hydroxyphenyl)pyrazoles have been prepared by the reaction of isoflavones and their 4-thio analogues with hydrazine hydrate and phenylhydrazine in hot pyridine. The reaction mechanism for the formation of these pyrazoles is discussed. All the new compounds have been fully characterized by NMR spectroscopy. In [D6]DMSO, a 1H NMR study allows observation of the presence of both pyrazole annular tautomers, due to the presence of intramolecular hydrogen bonds in each tautomer (OH···N and NH···O). Theoretical calculations have been carried out on tautomers and conformers of compounds 20 (3(5)-(2-hydroxy-4-methoxyphenyl)-5(3)-methyl-4-phenylpyrazole) and 21 (3(5)-(2-hydroxy-4-methoxyphenyl)-4-(2-methoxyphenyl)-5(3)-methylpyrazole), including the absolute shieldings (GIAO/B3 LYP/6–311++G**) of 21.

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