scholarly journals Anion influences on reactivity and NMR spectroscopic features of NHC precursors

RSC Advances ◽  
2018 ◽  
Vol 8 (61) ◽  
pp. 34960-34966 ◽  
Author(s):  
Han Vinh Huynh ◽  
Truc Tien Lam ◽  
Huyen T. T. Luong
Keyword(s):  
Coupling Constants ◽  
Azolium Salts ◽  
Hydrogen Bondings

The influences of 16 different counteranions on hydrogen-bondings, C–H acidities and 1JC2–H coupling constants of azolium salts have been studied.

Characterization of Hydrogen Bonds in the End-Functionalized Single-Wall Carbon Nanotubes: A DFT Study

NANO ◽  
2015 ◽  
Vol 10 (03) ◽  
pp. 1550036
Author(s):  
Reza Ghafouri ◽  
Fatemeh Ektefa ◽  
Mansour Zahedi
Keyword(s):  
Carbon Nanotubes ◽  
Hydrogen Bonding ◽  
Computational Study ◽  
Intramolecular Hydrogen Bonding ◽  
Nbo Analysis ◽  
Coupling Constants ◽  
Single Wall Carbon Nanotubes ◽  
Single Wall Carbon ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bondings

A systematic computational study is carried out to shed some light on the structure of semiconducting armchair single-wall carbon nanotubes (n, n) SWCNTs, n = 4, 5 and 6, functionalized at the end with carboxyl (– COOH ) and amide (– CONH 2) from the viewpoint of characterizing the intramolecular hydrogen bondings at the B3LYP/6-31++G(d, p) level. Geometry parameters display different types of intramolecular hydrogen bonding possibilities in the considered functionalized SWCNTs. All of the hydrogen bondings are confirmed by natural bonding orbitals (NBO) analysis as well as nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) parameters. Based on NBO analysis, the calculated [Formula: see text] delocalization energies E(2), 1.15 kcal/mol to 7.04 kcal/mol, are in direct relation with the hydrogen bonding strengths. Differences in the chemical shielding principal components of 13 C and 17 O nuclei correlate well with the strengths of the hydrogen bondings. Participating in stronger hydrogen bondings, a larger SWCNT has a decreasing effect on 13 C (= O ) and 17 O isotropic chemical shieldings, σiso, consistent with the NBO analysis. The considerable changes of 13 C /17 O σiso can be interpreted as a result of shielding tensor component orientation. The 13 C (= O ) and 17 O quadrupole coupling constants C Q decrease under the effect of hydrogen bonding while asymmetry parameters ηQ significantly increase, indicating that 17 O ηQ is more sensitive to hydrogen bondings.

Vibrational and thermal averaging of the indirect nuclear spin-spin coupling constants of CH4, SiH4, GeH4 and SnH4

1997 ◽  
Vol 91 (5) ◽  
pp. 897-907 ◽  
Author(s):  
SHEELA KIRPEKAR ◽  
THOMAS ENEVOLDSEN ◽  
JENS ODDERSHEDE ◽  
WILLIAM RAYNES
Keyword(s):  
Nuclear Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

$\mathit{Ab\!-\!initio}$ Determination of Magnetic Interface Coupling Constants for Magnetic Multilayers

1997 ◽  
Vol 7 (11) ◽  
pp. 1299-1304 ◽  
Author(s):  
P. Weinberger ◽  
C. Sommers ◽  
U. Pustogowa ◽  
L. Szunyogh ◽  
B. Újfalussy
Keyword(s):  
Ab Initio ◽  
Magnetic Multilayers ◽  
Coupling Constants ◽  
Interface Coupling

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model to Improve Density Function Calculations

2019 ◽  
Author(s):  
Xianghai Sheng ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Density Functional Theory ◽  
Exchange Coupling ◽  
Density Functional ◽  
Spin Crossover ◽  
Coupling Constants ◽  
Spin Projection ◽  
Coupling Constant ◽  
Projection Model ◽  
Functional Theory

This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the Approximate Projection model. Results show that improvements using the Approximate Projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin-projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin-projection can be important for both geometry optimization and energy evaluations. The Approximate Project model provides an affordable and practical approach for effectively correcting spin-contamination errors in molecular exchange coupling constant and spin crossover gap calculations.

The Electron Effect of Aromatic Group: Control Conformation of 2-Aromatic Cyclododecanone Derivatives

2020 ◽  
Vol 24 (10) ◽  
pp. 1139-1147
Author(s):  
Yang Mingyan ◽  
Wang Daoquan ◽  
Wang Mingan
Keyword(s):  
1H Nmr ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
The Other ◽  
Repulsive Interaction ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electron Effect ◽  
Group Control

2-Phenylcyclododecanone and 2-cyclohexylcyclododecanone derivatives were synthesized and characterized by 1H NMR, 13C NMR, HR-ESI-MS and X-ray diffraction. Their preferred conformations were analyzed by the coupling constants in the 1H NMR spectra and X-ray diffraction, which showed the skeleton ring of these derivatives containing [3333]-2-one conformation, and the phenyl groups were located at the side-exo position of [3333]-2-one conformation due to the strong π-π repulsive interaction between the π- electron of benzene ring and π-electron of carbonyl group. The cyclohexyl groups were located at the corner-syn or the side-exo position of [3333]-2-one conformation depending on the hindrance of the other substituted groups. The π-π electron effect played a crucial role in efficiently controlling the preferred conformation of 2-aromatic cyclododecanone and the other 2-aromatic macrocyclic derivatives with the similar preferred square and rectangular conformations.

Conformational structure of ethylene glycol dibenzoate. Vibrational and NMR spectra

1981 ◽  
Vol 46 (8) ◽  
pp. 1913-1929 ◽  
Author(s):  
Bohdan Schneider ◽  
Pavel Sedláček ◽  
Jan Štokr ◽  
Danica Doskočilová ◽  
Jan Lövy
Keyword(s):  
Ethylene Glycol ◽  
Vibrational Spectra ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Conformational Structure ◽  
Infrared And Raman Spectra ◽  
H Nmr ◽  
Liquid States ◽  
Crystalline Forms ◽  
C Nmr

It was found that three crystalline forms of ethylene glycol dibenzoate can be prepared. Infrared and Raman spectra of these three forms, as well as of the glassy and liquid states, were measured. From 3JHH coupling constants obtained by analysis of the 13C satellite band of the -CH2- group in 1H NMR spectra, and from the 3JCH coupling constants of the -CO.O.CH2- fragment obtained by analysis of the carbonyl band in 13C NMR spectra it was found that in the liquid state the -CH2-CH2- group exists predominantly in the gauche conformational structure, and the bonds C-O-C-C assume predominantly a trans orientation. The results of the analysis of NMR and vibrational spectra were used for the structural interpretation of conformationally sensitive bands in vibrational spectra of ethylene glycol dibenzoate.

13C nuclear magnetic resonance study of cyclodipeptides containing 13C enriched hydrophobic amino acids

1980 ◽  
Vol 45 (2) ◽  
pp. 482-490 ◽  
Author(s):  
Jaroslav Vičar ◽  
François Piriou ◽  
Pierre Fromageot ◽  
Karel Bláha ◽  
Serge Fermandjian
Keyword(s):  
Amino Acids ◽  
Nuclear Magnetic Resonance ◽  
Nuclear Magnetic Resonance Study ◽  
Coupling Constants ◽  
Side Chain ◽  
Amino Acid Residues ◽  
Magnetic Resonance Study ◽  
Side Chain Conformation ◽  
13C Nuclear Magnetic Resonance ◽  
Hydrophobic Amino Acids

The diastereoisomeric pairs of cyclodipeptides cis- and trans-cyclo(Ala-Ala), cyclo(Ala-Phe), cyclo(Val-Val) and cyclo(Leu-Leu) containing 85% 13C enriched amino-acid residues were synthesized and their 13C-13C coupling constants were measured. The combination of 13C-13C and 1H-1H coupling constants enabled to estimate unequivocally the side chain conformation of the valine and leucine residues.

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