Theoretical calculations of chemical interactions. VII. SCF-MO conformational studies of substituted 2′-hydroxychalcones

1991 ◽  
Vol 69 (5) ◽  
pp. 865-869 ◽  
Author(s):  
Norma Sbarbati Nudelman ◽  
Jorge Javier P. Furlong
Keyword(s):  
Hydrogen Bond ◽  
Theoretical Calculations ◽  
Slow Step ◽  
Chemical Interactions ◽  
Conformational Studies ◽  
Mndo Calculations ◽  
Indo Calculations ◽  
Intramolecular Hydrogen ◽  
Nmr Signals ◽  
Strong Barrier

INDO calculations have been performed on substituted 2′-hydroxychalcones. The results show that the intramolecularly hydrogen-bonded trans-s-cis conformation is the most stable. The calculations assist in assignment of NMR signals and interpretation of kinetic determinations. The calculated energy of the intramolecular hydrogen bond is compared with IR data when available and with experimentally determined heats of formation of the chalconates. Regarding the isomerization to flavanones, calculations of the ring A rotation in the chalconates show that it is exergonic; on the contrary, complete rotation of the styryl system encounters a strong barrier. MNDO calculations on this process show similar trends. These results indicate that this last rotation is involved in the slow step, which is consistent with kinetic determinations. Key words: chemical interactions, theoretical calculations, substituted hydroxychalcones, flavanones.

scholarly journals Conformational analysis of 2,2-difluoroethylamine hydrochloride: double gauche effect

2014 ◽  
Vol 10 ◽  
pp. 877-882 ◽  
Author(s):  
Josué M Silla ◽  
Claudimar J Duarte ◽  
Rodrigo A Cormanich ◽  
Roberto Rittner ◽  
Matheus P Freitas
Keyword(s):  
Hydrogen Bond ◽  
Electrostatic Interactions ◽  
Fluorine Atom ◽  
Theoretical Calculations ◽  
Water Solution ◽  
Coupling Constants ◽  
Secondary Importance ◽  
Gauche Effect ◽  
Intramolecular Hydrogen ◽  
Positively Charged

The gauche effect in fluorinated alkylammonium salts is well known and attributed either to an intramolecular hydrogen bond or to an electrostatic attraction between the positively charged nitrogen and the vicinal electronegative fluorine atom. This work reports the effect of adding a fluorine atom in 2-fluoroethylamine hydrochloride on the conformational isomerism of the resulting 2,2-difluoroethylamine chloride (2). The analysis was carried out using NMR coupling constants in D2O solution, in order to mimic the equilibrium conditions in a physiological medium, in the gas phase and in implicit water through theoretical calculations. Despite the presence of σCH→σ*CF and σCH→σ*CN interactions, which usually rule the hyperconjugative gauche effect in 1,2-disubstituted ethanes, the most important forces leading to the double gauche effect (+NH3 in the gauche relationship with both fluorine atoms) in 2 are the Lewis-type ones. Particularly, electrostatic interactions are operative even in water solution, where they should be significantly attenuated, whereas hyperconjugation and hydrogen bond have secondary importance.

Structural and conformational studies of 5-(1H-pyrrol-2-ylmethylene)-substituted imidazolidine-2,4-diones and thiazolidine-2,4-diones

2002 ◽  
Vol 80 (10) ◽  
pp. 1302-1307 ◽  
Author(s):  
Alfonso de Dios ◽  
Maria Luz de la Puente ◽  
Alfonso Rivera-Sagredo ◽  
Juan Felix Espinosa
Keyword(s):  
Hydrogen Bond ◽  
Double Bond ◽  
Aldol Condensation ◽  
Condensation Reaction ◽  
Trans Form ◽  
Stable Conformer ◽  
Nmr Studies ◽  
Conformational Studies ◽  
Temperature Coefficients ◽  
Intramolecular Hydrogen

Some imidazolidine-2,4-dione (hydantoin) and thiazolidine-2,4-dione (TZD) derivatives with a 1H-pyrrol-2-ylmethylene substituent at the 5-position (1–8) have been synthesized via an aldol condensation reaction. A mixture of Z- and E- stereoisomers was obtained, as confirmed by HPLC and NMR studies. Assignment of the stereochemistry was achieved through chemical shift knowledge, NOE, and 3JH,C data. The conformation of the molecules depends on the configuration at the double bond. While the (NH,C cis) form is the most stable conformer for the E-isomer, the (NH,C trans) form is the preferred conformer for the Z-isomer. The temperature coefficients of the NH pyrrole protons reveal the existence of an intramolecular hydrogen bond for the E-isomers.Key words: hydantoin, TZD, NMR spectroscopy, conformational analysis, temperature coefficient.

Correlating experimental electrochemistry and theoretical calculations in 2′-hydroxy chalcones: the role of the intramolecular hydrogen bond

RSC Advances ◽  
2015 ◽  
Vol 5 (63) ◽  
pp. 50929-50937 ◽  
Author(s):  
Maximiliano Martínez-Cifuentes ◽  
Ricardo Salazar ◽  
Carlos A. Escobar ◽  
Boris E. Weiss-López ◽  
Leonardo S. Santos ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Hydrogen Bond ◽  
Intramolecular Hydrogen Bond ◽  
Theoretical Calculations ◽  
Electrochemical Behaviour ◽  
Redox Properties ◽  
Methoxy Substituent ◽  
Intramolecular Hydrogen

The molecular structure and electrochemical behaviour of a series of 2′-hydroxychalcones were studied. Results show the importance of the intramolecular hydrogen bond and the methoxy substituent pattern on the redox properties of these compounds.

scholarly journals Study of Anti-Tuberculosis Activity Behaviour of Natural Kaurane and Trachylobane Diterpenes Compared with Structural Properties Obtained by Theoretical Calculations

2017 ◽  
Vol 12 (5) ◽  
pp. 1934578X1701200
Author(s):  
Ana C. F. Soares ◽  
Mirela M. W. Cabral ◽  
Carlos H. G. Martins ◽  
Alexsandro E. Ferreira ◽  
Pedro A. S. Bergamo ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Mycobacterium Tuberculosis ◽  
Structural Properties ◽  
Theoretical Calculations ◽  
Second Line ◽  
Homo And Lumo ◽  
Intramolecular Hydrogen ◽  
Activity Behaviour ◽  
Line Drug ◽  
Tuberculosis Activity

A set of seven diterpenes, three kauranes and four trachylobanes, isolated from the African plant Psiadia punctulata were assayed against Mycobacterium tuberculosis and reached activity comparable with cycloserine, a second line drug used to treat tuberculosis (TB). Several structural properties of those diterpenes, such as lipophilicity, HOMO and LUMO energies, charge density, and intramolecular hydrogen bond (IHB) formation, were obtained by theoretical calculations and compared with their activities. Peculiar correlations were observed, especially between activity, lipophilicity and IHB formation.

N-tert-Butyl-N′-[5-cyano-2-(4-methylphenoxy)phenylsulfonyl]urea, a new TXA2receptor antagonist

2013 ◽  
Vol 69 (8) ◽  
pp. 901-903
Author(s):  
Sylvie-Mireille Bambi-Nyanguile ◽  
Peter Mangwala Kimpende ◽  
Bernard Pirotte ◽  
Luc Van Meervelt
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Crystal Packing ◽  
Theoretical Calculations ◽  
Intramolecular Hydrogen Bonding ◽  
Asymmetric Unit ◽  
Dimer Formation ◽  
Compound C ◽  
Structural Database ◽  
Intramolecular Hydrogen

The title compound, C19H21N3O4S, crystallizes in the space groupP2/cwith two molecules in the asymmetric unit. The conformation of both molecules is very similar and is mainly determined by an intramolecular N—H...O hydrogen bond between a urea N atom and a sulfonyl O atom. The O and second N atom of the urea groups are involved in dimer formationviaN—H...O hydrogen bonds. The intramolecular hydrogen-bonding motif and conformation of the C—SO2—NH(C=O)—NH—C fragment are explored and compared using the Cambridge Structural Database and theoretical calculations. The crystal packing is characterized by π–π stacking between the 5-cyanobenzene rings.

Dipole moment of the intramolecular hydrogen bond. 2-Nitrophenol and its derivatives

1983 ◽  
Vol 48 (3) ◽  
pp. 735-747 ◽  
Author(s):  
Otto Exner ◽  
Juraj Koudelka ◽  
Soňa Vašíčková
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Dipole Moment ◽  
Intramolecular Hydrogen Bond ◽  
Dipole Moments ◽  
Charge Redistribution ◽  
Experimental Dipole Moment ◽  
Mndo Calculations ◽  
The Difference ◽  
Intramolecular Hydrogen

Dipole moments of substituted 2-nitrophenols VIa-VIf and substituted 2-nitroanisoles VIIa to VIIf were measured in benzene and dioxan solutions. Infrared spectroscopy confirmed that nitrophenols VI exist either solvent and at different concentrations as non-associated molecules with an intramolecular hydrogen bond. Therefore, the difference between the experimental dipole moment and that calculated from group moments can be attributed to charge redistribution raised by the hydrogen bond. Only a minute part of it may be due to electron transfer through the ring (conjugation of the functional groups) as follows particularly from he comparison with nitroanisoles VII. Nevertheless, the charge transfer, expressed as the vector μH, amounts only 1.7 . 10-30 Cm (at an angle of 138° to the H-O bond), i.e. several times less than observed previously in compounds with more powerful hydrogen acceptors. CNDO/2 and MNDO calculations agree fairly with the gross dipole moments of the compounds investigated but are unable to predict μH, not even as far as its direction is concerned.

Theoretical calculations of intramolecular hydrogen bond of the 2-Amino-2, 4, 6-cycloheptatrien-1-one in the gas phase and solution: Substituent effects and their positions

2016 ◽  
Vol 15 (07) ◽  
pp. 1650063 ◽  
Author(s):  
Narges Khatoon Attaran Toosy ◽  
Heidar Raissi ◽  
Maryam Zaboli
Keyword(s):  
Hydrogen Bond ◽  
Gas Phase ◽  
Intramolecular Hydrogen Bond ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Substituent Effects ◽  
Dft Method ◽  
Basis Set ◽  
Parent Molecule ◽  
Intramolecular Hydrogen

The density functional theory (DFT) method with 6-311[Formula: see text]G[Formula: see text] basis set has been used to calculate the intramolecular hydrogen bond, molecular structure, vibrational frequencies, nuclear quadrupole resonance (NQR) parameters, 1HNMR, and resonance parameters of 2-Amino-2, 4, 6-cycloheptatrien-1-one (2-amino tropone) and its 18 derivatives in 5 positions. The natural bonding orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses have been studied. The strongest and weakest hydrogen bonds exist for NO2 substituent in R3 position and OH in R7 position, respectively. In general, the substituted systems in position 3 indicate the stronger hydrogen bond in comparison with the parent molecule (R[Formula: see text]H), while, it is comparatively weaker for position 5. The energy of the N-H[Formula: see text]O interaction is found to be medium in strength ([Formula: see text][Formula: see text]kJ mol[Formula: see text] to [Formula: see text][Formula: see text]kJ mol[Formula: see text]). The low [Formula: see text], positive [Formula: see text] values and [Formula: see text] show that the nature of O [Formula: see text] H bonding is electrostatic. Also, our theoretical results show that the hydrogen bond strength in solution phase and the first singlet excited state is weaker in comparison with the gas phase ground state.

Difference between 1 H NMR signals of primary amide protons as a simple spectral index of the amide intramolecular hydrogen bond strength

2011 ◽  
Vol 25 (4) ◽  
pp. 287-295 ◽  
Author(s):  
Nikolay Yu. Gorobets ◽  
Sergey A. Yermolayev ◽  
Thomas Gurley ◽  
Andrey A. Gurinov ◽  
Peter M. Tolstoy ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Bond Strength ◽  
Intramolecular Hydrogen Bond ◽  
Spectral Index ◽  
Primary Amide ◽  
H Nmr ◽  
Hydrogen Bond Strength ◽  
Intramolecular Hydrogen ◽  
Nmr Signals ◽  
Amide Protons
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