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.

scholarly journals Complexation of Cu(BF4)2 with 3-hydroxyflavone in acetonitrile: quantum chemical calculation

2018 ◽  
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Atom ◽  
Intramolecular Hydrogen Bond ◽  
Quantum Chemical ◽  
Phenyl Ring ◽  
Fluorine Atom ◽  
Quantum Chemical Study ◽  
Hydroxyl Group ◽  
Chemical Calculation ◽  
Intramolecular Hydrogen

In the article the results of the quantum chemical study of copper (II) solvato-complexes with acetonitrile (AN), tetrafluoroborate anion (BF4–) and 3-hydroxyflavone (flv) of the composition [Cu(AN)6]2+, [Cu(BF4)(AN)5]+, [Cu(flv)(AN)5]2+, [Cu(flv)(BF4)(AN)4]+ are presented. Calculations were done using density function theory (DFT) on the M06-2X/6-311++G(d,p) level of theory. Obtained results were interpreted in terms of complexes geometry and topology of electron density distribution using non-covalent interactions (NCI) approach. It was shown that flv molecule is a monodentate ligand in copper (II) complexes and coordinates central atom via carbonyl oxygen. Intramolecular hydrogen bond that exists in an isolated flv molecule was found to be broken upon [Cu(flv)(AN)5]2+ complex formation. In [Cu(flv)(AN)5]2+ complex, a significant rotation of phenyl ring over the planar chromone fragment was spotted as a consequence of intramolecular hydrogen bond breaking. Upon inclusion of BF4– anion to the first solvation shell of Cu2+, an intracomplex hydrogen bond was formed between hydrogen atom of hydroxyl group of flv molecule and the closest fluorine atom of BF4– anion. NCI analysis had shown that a hydrogen bond between hydrogen atom of hydroxyl group of flv molecule and the closest fluorine atom of BF4– anion is significantly stronger than intramolecular hydrogen bond in an isolated flv molecule. In addition, flexible phenyl ring of flv molecule in [Cu(flv)(BF4)(AN)4]+ complex was found to be internally stabilized by the weak van der Waals attraction between oxygen atoms of chromone ring and phenyl hydrogens. These evidences led to a conclusion that [Cu(flv)(BF4)(AN)4]+ complex is more stable, comparing to the in [Cu(flv)(AN)5]2+ complex.

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.

Intramolecular Hydrogen Bond Reverting the Solvent Effect on Phosphorus Hyperfine Coupling Constants of β-Phosphorylated Nitroxides

ChemPhysChem ◽  
2016 ◽  
Vol 17 (23) ◽  
pp. 3954-3963 ◽  
Author(s):  
Gérard Audran ◽  
Lionel Bosco ◽  
Paul Brémond ◽  
Teddy Butscher ◽  
Sylvain R. A. Marque ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Solvent Effect ◽  
Intramolecular Hydrogen Bond ◽  
Hyperfine Coupling ◽  
Coupling Constants ◽  
Hyperfine Coupling Constants ◽  
Intramolecular Hydrogen

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.

Large perturbations of long-range nJ(1H,1H) and nJ(1H,19F) by the intramolecular hydrogen bonds in 2-mercaptobenzaldehyde, salicylaldehyde, and some derivatives. Reference structures for intramolecular hydrogen bonds

1993 ◽  
Vol 71 (7) ◽  
pp. 960-967 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
David M. McKinnon ◽  
Perry W. Spevack ◽  
Kerry J. Cox ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Long Range ◽  
Bond Formation ◽  
Coupling Constants ◽  
Hydrogen Bond Formation ◽  
Intramolecular Hydrogen Bonds ◽  
Large Perturbation ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bonded

Precise 1H nuclear magnetic resonance spectral parameters are reported for salicyladehyde and its 3-fluoro and 5-fluoro derivatives in nonpolar solutions. Such data are also given for the 2-mercapto, 2-methylthio, and 2-methoxy derivatives of benzaldehyde. Comparison of the long-range coupling constants in the various compounds and their conformers shows a large perturbation of their magnitudes by hydrogen bond formation. For the salicylaldehyde system, the perturbation is particularly large for couplings involving the aldehyde proton and protons or fluorine nuclei placed ortho to the hydroxyl group. For example, 5Jt (F, CHO) is reduced by about 50%. The perturbation, as expected, is much smaller for coupling constants of nuclei remote from the site of the hydrogen bond. In 2-mercaptobenzaldehyde the long-range coupling constants are also sensitive to hydrogen bond formation, those involving the sulfhydryl proton markedly so compared to the hydroxyl proton in salicylaldehyde. The strength of the [Formula: see text] bond is discussed. It is argued that the reference conformer for the mercapto compound in such a discussion is less easily defined than for salicylaldehyde because [Formula: see text] are similar to [Formula: see text] energies. The experimental data for the CCl4 solutions imply a free energy of formation of the [Formula: see text] bond of 4.8(5) kJ/mol at 300 K. Molecular orbital computations on the four planar conformers of each salicylaldehyde and 2-mercaptobenzaldehyde with the 6-31 G**(5D) basis are reported. For salicylaldehyde, the [Formula: see text] arrangement is taken as the reference conformer, with a computed energy of 25.7 kJ/mol relative to the hydrogen-bonded structure. For 2-mercaptobenzaldehyde, the [Formula: see text] and [Formula: see text] conformers are calculated to be isoenergetic, at 5.1 kJ/mol relative to the hydrogen-bonded conformer. Hence either arrangement serves as a reference structure in computations of the strength of the hydrogen bond. The computations are consistent with the experimental results for solutions of the molecules under discussion. An appendix gives the computed geometries of the eight planar conformers, as well as some atomic charges, allowing a rationalization of the relative energies of the conformers.

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.

scholarly journals Simulation of Intramolecular Hydrogen Bond Dynamics in Manzamine A as a Sensitive Test for Charge Distribution Quality

2012 ◽  
Vol 7 (3) ◽  
pp. 1934578X1200700
Author(s):  
Dmitry A. Shulga ◽  
Dmitry I. Osolodkin ◽  
Vladimir A. Palyulin ◽  
Nikolay S. Zefirov
Keyword(s):  
Hydrogen Bond ◽  
Charge Distribution ◽  
Intramolecular Hydrogen Bond ◽  
Water Solution ◽  
Test Case ◽  
Manzamine A ◽  
Structure And Dynamics ◽  
Hydrogen Bond Strength ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bond Dynamics

Subtle balance of inter- and intramolecular hydrogen bond strength in aqueous solutions often governs the structure and dynamics of molecular species used as potential drugs and in supramolecular applications. In silico molecular dynamics study of water solution of manzamine A has been performed with different atomic charges in order to investigate the influence of charge distribution choice on predicting qualitative and quantitative features of the simulated systems. Various well known charge schemes (MK-ESP, RESP, Mulliken, AM1-BCC, Gasteiger-Hückel, Gasteiger-Marsili, MMFF94, and Dynamic Electronegativity Relaxation - DENR) led to qualitatively different pictures of dynamic behavior of the intramolecular hydrogen bond. The reported calculation framework represents a relatively rare case where differences in charge distributions lead to noticeable differences in simulated properties, thus providing a useful test case for force field and charge distribution development, provided high quality experiments are conducted to use as references.

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