NMR of Enaminones Part 3—1H,13C and17O NMR Spectroscopic Studies of Acyclic and CyclicN-Aryl Enaminones: Substituent Effects and Intramolecular Hydrogen Bonding

1997 ◽  
Vol 35 (5) ◽  
pp. 311-322 ◽  
Author(s):  
Jin-Cong Zhuo
Keyword(s):  
Hydrogen Bonding ◽  
Substituent Effects ◽  
Intramolecular Hydrogen Bonding ◽  
Spectroscopic Studies ◽  
Intramolecular Hydrogen

Beziehungen zwischen Rotationsisomerie, Wasserstoffbrücken-Bindung und Substituenteneffekten der organischen Chemie / Relations between Rotational Isomerism, Hydrogen Bonding, and Substituent Effects in Organic Chemistry

1972 ◽  
Vol 27 (6) ◽  
pp. 663-674 ◽  
Author(s):  
Gotthard H. Krause ◽  
Herbert Hoyer
Keyword(s):  
Hydrogen Bonding ◽  
Substituent Effects ◽  
Intramolecular Hydrogen Bonding ◽  
Rotational Isomerism ◽  
Proton Acceptor ◽  
Single Bond ◽  
Free Enthalpy ◽  
Acceptor Group ◽  
Intramolecular Hydrogen ◽  
Derivatives Of

The change of free enthalpy involved in intramolecular hydrogen bonding is smaller if the proton acceptor group can rotate round a single bond, as compared to proton acceptor groups which are fixed in a position optimal for hydrogen bonding. Also, the free enthalpy change is altered when the rotation of the proton acceptor is sterically restricted. This is demonstrated by comparing the absorptions of carbonyl stretching vibrations in the infrared spectra of certain compounds showing rotational isomerism. In the present study derivatives of 5-hydroxy-2,2-dimethyl-6-carbomethoxychromanone- (4), 3-nitrosalicylaldehyde and 3-nitro-2-hydroxy-acetophenones substituted in the position 5 and 6 are examined.

Crystal structure, spectroscopic studies and theoretical studies of thiobarbituric acid derivatives: understanding the hydrogen-bonding patterns

2018 ◽  
Vol 74 (12) ◽  
pp. 1703-1714 ◽  
Author(s):  
Anamika Sharma ◽  
Sizwe J. Zamisa ◽  
Sikabwe Noki ◽  
Zainab Almarhoon ◽  
Ayman El-Faham ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Materials Science ◽  
Thiobarbituric Acid ◽  
Intramolecular Hydrogen Bonding ◽  
Spectroscopic Studies ◽  
Enol Form ◽  
Keto Form ◽  
X Ray Crystallography ◽  
Schiff Base Formation ◽  
Intramolecular Hydrogen

In addition to their wide-ranging applications in the pharmaceutical industry, thiobarbituric acid (TBA) derivatives are also known to possess applications in engineering and materials science. 20 TBA derivatives, with diversity at the N and C-5 positions through acylation, Schiff base formation, Knoevenagel condensation, thioamide and enamine formation, were studied. The absolute configurations for six derivatives, namely 5-acetyl-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C10H14N2O3S, A01, 1,3-diethyl-5-propionyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C11H16N2O3S, A02, tert-butyl [1-(1,3-diethyl-4,6-dioxo-2-thioxohexahydropyrimidin-5-yl)-3-methyl-1-oxobutan-2-yl]carbamate, C18H29N3O5S, A06, 1,3-diethyl-4,6-dioxo-2-thioxo-N-(p-tolyl)hexahydropyrimidine-5-carbothioamide, C16H19N3O2S2, A13, 5-(1-aminoethylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C10H15N3O2S, A17, and 5-(1-aminopropylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, C11H17N3O2S, A18, were confirmed by single-crystal X-ray crystallography, which indicates the formation of intramolecular hydrogen bonding in all six cases and intermolecular hydrogen bonding for A17. In A13, the presence of two intramolecular hydrogen bonds was observed. The stabilization of the enol form over the keto form was confirmed by computation. In order to convert the keto form to the enol form, an energy barrier of 55.05 kcal mol−1 needs to be overcome, as confirmed by transition-state calculations.

EFFECT OF INTRAMOLECULAR HYDROGEN BONDING ON IONIZATION CONSTANTS OF SUBSTITUTED SALICYLIC ACIDS

1966 ◽  
Vol 44 (11) ◽  
pp. 1261-1269 ◽  
Author(s):  
G. E. Dunn ◽  
Fei-lin Kung
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Spectrophotometric Method ◽  
Chelate Ring ◽  
Substituent Effects ◽  
Intramolecular Hydrogen Bonding ◽  
Ionization Constants ◽  
Intramolecular Hydrogen ◽  
Hammett Relationship ◽  
Salicylic Acids

Ionization constants at 25 °C have been determined by a spectrophotometric method for 17 substituted salicylic acids. These have been fitted to the simple Hammett relationship and to the extended one proposed by Jaffe, which takes into account the transmission of substituent effects by the o-hydroxy group. The results with Jaffe's equation show that substituent effects on acidity are transmitted only slightly, if at all, through the intramolecular hydrogen bond of a chelate ring. Possible interpretations of the results are discussed.

scholarly journals Substituent Effects on Pyrid-2-yl Ureas toward Intramolecular Hydrogen Bonding and Cytosine Complexation

2004 ◽  
Vol 69 (6) ◽  
pp. 1866-1871 ◽  
Author(s):  
Chia-Hui Chien ◽  
Man-kit Leung ◽  
Jen-Kuan Su ◽  
Gene-Hsiang Li ◽  
Yi-Hung Liu ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Substituent Effects ◽  
Intramolecular Hydrogen Bonding ◽  
Intramolecular Hydrogen
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