Concerning the internal rotational barrier and the experimental and theoretical nJ(13C,13C) and nJ (1H,13C) in ethylbenzene-β-13C

1994 ◽  
Vol 72 (9) ◽  
pp. 1972-1977 ◽  
Author(s):  
Ted Schaefer ◽  
Wing K. Chan ◽  
Rudy Sebastian ◽  
Robert Schurko ◽  
Frank E. Hruska
Keyword(s):  
Nmr Spectra ◽  
Coupling Constants ◽  
Carbon Nucleus ◽  
Valence Orbital ◽  
Stable Conformer ◽  
Torsion Angles ◽  
H Nmr ◽  
Nuclear Magnetic Resonance Spectra ◽  
Experimental Values ◽  
Optimized Geometries

The 1H nuclear magnetic resonance spectra of ethylbenzene-β-13C in CS2/C6D12 and acetone-d6 solutions yield long-range 1H,1H and 1H,13C coupling constants. The 13C {1H} NMR spectra yield 13C, 13C couplings. The conformational dependence of some of these coupling constants is compatible with two values of the barrier to internal rotation about the exocyclic Csp2—Csp3 bond. If the fourfold component of the internal rotational potential is not larger than about 20% of the twofold component and the perpendicular conformer is most stable, then the barrier height is probably less than 6 kJ/mol. However, if the stable conformer has a torsion angle of 60° for the exocyclic C—C bond, then the coupling constants are consistent with a twofold barrier of about 23 kJ/mol. Experimental values of [Formula: see text] and [Formula: see text], where ψ and θ are the torsion angles for the exocyclic C—C and C—H bonds, respectively, are compared to those obtained from INDO MO FPT computations of the angular dependence of nJ(H,C), and nJ(H,H), nJ(C,C) for n ≥ 3. For example, the computations very likely give the correct qualitative ψ dependence of 5J(C,C), yet overestimate its extremum by about a factor of two, either because of an overestimate of the σ–π exchange integrals or because of too large a valence orbital density at the carbon nucleus. Other nJ values are discussed in a similar manner and, because optimized geometries are used in the computations, a somewhat more reliable treatment arises for some coupling constants; an example is 3J(C,C) at small torsion angles.

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.

15N, 13C, and 1H NMR Spectra of Azo and Hydrazo Compounds Derived from 1,3,3-Trimethyl-2-methylidene-2,3-dihydroindole (Fischer Base)

1998 ◽  
Vol 63 (7) ◽  
pp. 1012-1020 ◽  
Author(s):  
Antonín Lyčka ◽  
Josef Jirman ◽  
Alois Koloničný
Keyword(s):  
Double Bond ◽  
Hydrochloric Acid ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Azo Compounds ◽  
Passive Component ◽  
Geometric Isomers ◽  
H Nmr ◽  
Fischer Base ◽  
Hydrazone Form

The 15N, 13C, and 1H NMR spectra were measured for azo and hydrazo compounds derived from 1,3,3-trimethyl-2-methylidene-2,3-dihydroindole (Fischer base), which is a passive component with a terminal methylidene group. Products prepared by coupling in hydrochloric acid exist in the corresponding hydrazone form as the E-isomers. Neutralization gives a mixture of two isomeric azo compounds which differ in the arrangement at the C(2)=C(10) double bond. This mixture was alkylated with methyl iodide to obtain the =N-N(CH3)- hydrazone derivatives. The geometric isomers were resolved based on the NOESY approach and the stereospecific behaviour of the 2J(15N,13C) coupling constants was studied for the 15N-labelled compounds.

The High Resolution NMR Spectra of Pesticides. II. The DDT-Type Compounds

1969 ◽  
Vol 52 (5) ◽  
pp. 1074-1092 ◽  
Author(s):  
L H Keith ◽  
A L Alford ◽  
A W Garrison
Keyword(s):  
Nuclear Magnetic Resonance ◽  
High Resolution ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Aromatic Rings ◽  
Nuclear Magnetic Resonance Spectra ◽  
High Resolution Nmr ◽  
Related Compounds ◽  
Deshielding Effect

Abstract The high resolution nuclear magnetic resonance spectra of the DDT class of pesticides and related compounds are discussed, including a study of the resonances of the aromatic protons as they are affected by various substiluents. The CCl3 moiety on the α-carbon strongly deshields the ortho protons on the aromatic rings, and this deshielding effect is greatly enhanced by substitution of a chlorine ortho rather than para on the aromatic ring. These deshielding effects are explained by a consideration of the electronegativity of the substituents and the stereochemistry of the molecule. The chemical shifts and coupling constants are tabulated.

E-Homolupane Derivatives Substituted in Position 17 and 22a. 1H NMR, 13C NMR and IR Spectra

1995 ◽  
Vol 60 (4) ◽  
pp. 619-635 ◽  
Author(s):  
Václav Křeček ◽  
Stanislav Hilgard ◽  
Miloš Buděšínský ◽  
Alois Vystrčil
Keyword(s):  
Nmr Spectra ◽  
2D Nmr ◽  
Coupling Constants ◽  
Side Chain ◽  
Oxidation Reactions ◽  
H Nmr ◽  
Complete Assignment ◽  
Nmr Techniques ◽  
Intramolecular Association ◽  
C Nmr

A series of derivatives with various oxygen functionalities in positions 17,22a or 19,20 was prepared from diene I and olefin XVI by addition and oxidation reactions. The structure of the obtained compounds was confirmed by 1H NMR, 13C NMR and IR spectroscopy. The kind of intramolecular association of the 17α-hydroxy group was studied in connection with modification of the side chain and substitution in position 22a. Complete assignment of the hydrogen signals and most of the coupling constants was accomplished using a combination of 1D and 2D NMR techniques. The 1H and 13C NMR spectra are discussed.

The High Resolution NMR Spectra of Pesticides. III. The Carbamates

1970 ◽  
Vol 53 (1) ◽  
pp. 157-179 ◽  
Author(s):  
L H Keith ◽  
A L Alford
Keyword(s):  
Nuclear Magnetic Resonance ◽  
High Resolution ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Hindered Rotation ◽  
Solvent Dependence ◽  
Nuclear Magnetic Resonance Spectra ◽  
High Resolution Nmr ◽  
Proton Resonances

Abstract The high resolution nuclear magnetic resonance spectra of 35 carbamate pesticides and a major metabolite of one pesticide are discussed. The chemical shifts and coupling constants are tabulated and reproductions of the more complex or unusual spectra are included. A concentration and solvent dependence of both the NH-proton and the NCH3-proton resonances of an N-monosubstituted carbamate is discussed. Hindered rotation is observed in the N,N-dimethylcarbamates, the thiolcarbamates and the dithiocarbamates, but not in the N-methylcarbamates.

Deuterium Quadrupolar Parameters from 1H and 2H NMR Spectra for Pyridine-d5, Benzonitrile-d5 and Chlorobenzene-d5 Using Liquid Crystal Solvents

1986 ◽  
Vol 41 (1-2) ◽  
pp. 431-435 ◽  
Author(s):  
R. Ambrosetti ◽  
D. Catalano ◽  
C. Forte ◽  
C. A. Veracini
Keyword(s):  
Liquid Crystal ◽  
Nmr Spectra ◽  
Order Parameters ◽  
Dipolar Couplings ◽  
Coupling Constants ◽  
2H Nmr ◽  
H Nmr ◽  
Quadrupolar Coupling ◽  
Asymmetry Parameters ◽  
Quadrupolar Splittings

T he quadrupolar coupling constants (DQCC) and the asymmetry parameters (η) for the ortho, meta and para deuterons in pyridine-d5, benzonitrile-d5 and chlorobenzene-d5 were determined by NMR spectroscopy in oriented phases. The 1H and 2H NMR spectra were recorded in the following solutions in liquid crystal solvents: pyridine + pyridine-d5 in PCH , in ZLI 1167 and in EBBA; benzonitrile + benzonitrile-d5 and chlorobenzene + chlorobenzene-d5 in the same solvents.The order parameters of the non-deuterated solutes in the various solutions were calculated using the dipolar couplings of the proton spectra and the rα structures taken from the literature. The same order parameters were assumed to describe also the orientation of the deuterated solute in the corresponding solutions.Each 2H spectrum yielded three quadrupolar splittings for the three different deuterated positions in the labelled solute. The splittings from the three different solutions of the same solute, together with the order parameters and the rα structure, were used to determine DQCC and η of the ortho, meta and para deuterons (Pyridine-d5: DQCCortho= 183(1) kHz, ηortho = 0.030(5), DQCCmeta = 185(1) kHz, ηmeta = 0.030(10), DQCCpara = 188(6) kHz, ηpara = 0.01(5). Benzonitrile-d5: DQCCortho = 171(12) kHz, ηortho = 0.07(3), DQCCmeta = 175(12) kHz, ηmeta = 0.05(3), DQCCpara = 176(4) kHz, ηpara = 0.10(7). Chlorobenzene-d5: DQCCortho = 180(2) kHz, ηortho = 0.06(1), DQCCmeta = 174(2) kHz, ηmeta = 0.09(3), DQCCpara= 182(4) kHz, ηPara = 0.06(4)). The results are discussed, as well as the limits and possibilities of the method used.

Experimental and theoretical assessments of the substituent and medium dependence of the internal rotational potentials in benzyl fluoride. 3,5-Difluorobenzyl fluoride and 4-fluorobenzyl fluoride

1995 ◽  
Vol 73 (6) ◽  
pp. 816-825 ◽  
Author(s):  
Ted Schaefer ◽  
Robert W. Schurko ◽  
Rudy Sebastian ◽  
Frank E. Hruska
Keyword(s):  
Parent Compound ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Stable Conformer ◽  
Fluoro Derivative ◽  
Theoretical Approaches ◽  
Spin Coupling Constants ◽  
Experimental Values ◽  
Spin Spin Coupling ◽  
Fluoro Derivatives

The 1H, 19F, and 13C {H} nuclear magnetic resonance spectra at 300 K of 4-fluoro- and 3,5-difluorobenzyl fluoride, dissolved in CS2–C6D12 and acetone-d6, are fully analyzed. Spin–spin coupling constants over four, five, and six formal bonds are used to derive expectation values of sin2θ and [Formula: see text] and the apparent twofold internal rotational potentials; [Formula: see text] is the angle by which the α C—F(C—H) bond twists out of the ring plane. The conformation of lowest energy has [Formula: see text] for the 3,5-difluoro compound in the polar and nonpolar solutions, whereas it has [Formula: see text] for the 4-fluoro derivative. The magnitudes of the potentials lie between 2 and 4 kJ/mol, that is, comparable to thermal energies. These data are compared with previous results for the parent compound and its 3,5-dichloro derivative. Geometry-optimized molecular orbital computations, including some correlation-gradient procedures, for benzyl fluoride and the two fluoro derivatives have [Formula: see text] for the conformations of highest energy of the free molecules. However, geometry-optimized SCFRF calculations of the solvent perturbations of the potential (dipole terms are insufficient) are in semiquantitative agreement with experiment in the sense that both solvents are predicted to destabilize the conformation with [Formula: see text] For example, the predominant twofold component in the computed (6-31G*) potential is 3.4 (free), −0.7 (CS2), and −3.3 (acetone-d6) kJ/mol for benzyl fluoride, a negative number indicating [Formula: see text] for the stable conformer; the experimental values are −0.8(2) (CS2) and −2.7(2) (acetone-d6) kJ/mol. The agreement between experiment and theory is of a similar quality for the fluoro derivatives. The stabilization of the conformer with [Formula: see text] for the 4-fluoro derivative is tentatively attributed to hyperconjugative electron acceptance by the α C—F bond, enhanced by the π-electron donor at the para position. A number of coupling constants are discussed in terms of the possible mechanisms of their transmission. Future experiments are indicated. Keywords: 1H, 19F, 13C NMR of 4-fluorobenzyl fluoride and 3,5-difluorobenzyl fluoride; MO calculations and internal rotational potentials in benzyl fluoride, 3,5-difluorobenzyl fluoride, and 4-fluorobenzyl fluoride; solvent effects and experimental and theoretical approaches to internal rotational potentials in 3,5-difluorobenzyl fluoride and 4-fluorobenzyl fluoride.

sHigh resolution 1H nuclear magnetic resonance studies of a flavine and its product with MoCl4

1977 ◽  
Vol 55 (4) ◽  
pp. 575-582 ◽  
Author(s):  
T. Roberie ◽  
N. S. Bhacca ◽  
J. Selbin
Keyword(s):  
Aqueous Solution ◽  
Nuclear Magnetic Resonance ◽  
Binding Sites ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Side Chain ◽  
Magnetic Resonance Studies ◽  
H Nmr ◽  
Metal Atoms ◽  
1H Nuclear Magnetic Resonance

The high resolution 1H nmr spectra of the substituted flavine, 3-N-methyltetraacetylriboflavine (3-Me-TARF), and its non-aqueous solution complexes with Gd(fod)3, Eu(fod)3, MoCl4, and MoCl4•2CH3(CH2)2CN, were studied in order to try to discern the binding sites of the flavine as it attaches to the molybdenum. Evidence was found that all three metal atoms, Gd(III), Eu(III), and Mo(IV), are attached in solution not only by the primary binding (chelating) sites of the flavine, viz., the O-4 and N-5 atoms, but also by an acetyl oxygen atom, at the C-4′ site of the ribityl side chain. 300 MHz spectra of the 3-Me-TARF have permitted the coupling constants for the side chain methine and methylene protons to be obtained.

scholarly journals Carbon-13 nuclear magnetic resonance spectra of oxazoles

1979 ◽  
Vol 57 (23) ◽  
pp. 3168-3170 ◽  
Author(s):  
Henk Hiemstra ◽  
Hendrik A. Houwing ◽  
Okko Possel ◽  
Albert M. van Leusen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Proton Coupling ◽  
Nuclear Magnetic Resonance Spectra ◽  
C Nmr ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13C nmr spectra of oxazole and eight mono- and disubstituted derivatives have been analyzed with regard to the chemical shifts and the various carbon–proton coupling constants of the ring carbons. The data of the parent oxazole are compared with thiazole and 1-methylimidazole.

Notizen: Geminal Coupling Constants 2.J(15N13C) in 2-Substituted Pyridines, Measured by Hahn-Echo Extended (HEED) Pulse Sequences

1993 ◽  
Vol 48 (10) ◽  
pp. 1433-1436
Author(s):  
Bernd Wrackmeyer ◽  
Gerald Kehr
Keyword(s):  
High Resolution ◽  
Nmr Spectra ◽  
Pulse Sequences ◽  
Coupling Constants ◽  
Positive Sign ◽  
Two Dimensional ◽  
H Nmr ◽  
Substituted Pyridines ◽  
Geminal Coupling

Coupling constants 2J(15N13CR) and nJ(15N1HR) in 2-substituted pyridines [R = Me (1), CH=CH2 (2), C≡CH (3), C(O)H (4), C(O)Me (5)] have been measured by using Hahn-echo extended (HEED) pulse sequences for one- (1 D) and two-dimensional (2D) 13C/1H NMR (HEED-INEPT, HEED-HETCOR). The magnitude of |2J(15N13CR)| is hardly affected by the hybridization of 13CR. 15N NMR spectra, measured under conditions of ultra high resolution (UHR) confirm the values 2J(15N13CR). 2D 13C/1H HEED-HETCOR experiments show that the sign of 3J(15Ν1HR) is negative in 1, whereas the coupling constants 3J(15N1HR) in 4 and 4J(15N1HR) in 3 have a positive sign

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