Signs of spin–spin coupling constants between aldehydic and ring protons in 2,6-dinitrobenzaldehyde. Evidence for a hyperconjugative contribution to JpH,CHO

1969 ◽  
Vol 47 (19) ◽  
pp. 3529-3533 ◽  
Author(s):  
C. L. Bell ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Aldehyde Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Para Position ◽  
Steric Interaction ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The spin–spin coupling constant between the aldehydic proton and the proton in the para position, JpH,HCO is negative in 2,6-dinitrobenzaldehyde. JpH,CHO is also very likely negative in 2,6-dichlorobenzaldehyde. It is suggested that steric interaction with the ortho substituents forces the aldehyde group out of a coplanar conformation and leads to an interaction of the aldehydic C–H bond with the π system of the ring. Tentative values of θ, a measure of the deviation from coplanarity, are given.

An estimate of the spin–spin coupling constant, 1J(1H,13C), in gaseous benzene

1996 ◽  
Vol 74 (8) ◽  
pp. 1524-1525 ◽  
Author(s):  
Ted Schaefer ◽  
Guy M. Bernard ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Dielectric Constant ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Gaseous Benzene

An excellent linear correlation (r = 0.9999) exists between the spin–spin coupling constants 1J(1H,13C), in benzene dissolved in four solvents (R. Laatikainen et al. J. Am. Chem. Soc. 117, 11006 (1995)) and Ando's solvation dielectric function, ε/(ε – 1). The solvents are cyclohexane, carbon disulfide, pyridine, and acetone. 1J(1H,13C)for gaseous benzene is predicted to be 156.99(2) Hz at 300 K. Key words: spin–spin coupling constants, 1J(1H,13C) for benzene in the vapor phase; spin–spin coupling constants, solvent dielectric constant dependence of 1J(1H,13C) in benzene; benzene, estimate of 1J(1H,13C) in the vapor; nuclear magnetic resonance, estimate of 1J(1H,13C) in gaseous benzene.

Anisotropy of indirect spin–spin coupling constants from nuclear magnetic resonance powder patterns of rigid solids. 1J(31P,199Hg) in [HgP(o-tolyl)3(NO3)2]2

1988 ◽  
Vol 66 (8) ◽  
pp. 1821-1823 ◽  
Author(s):  
Glenn H. Penner ◽  
William P. Power ◽  
Roderick E. Wasylishen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constants ◽  
Fermi Contact ◽  
Spin Spin Coupling ◽  
Contact Mechanism ◽  
Nuclear Magnetic

The anisotropy of the indirect 31P,199Hg spin–spin coupling constant, ΔJ, in solid [HgP(o-tolyl)3(NO3)2]2 is obtained from an analysis of the 31P nuclear magnetic resonance powder pattern. The value of ΔJ, 5170 ± 250 Hz, is large and indicates that mechanisms other than the Fermi contact mechanism are important for this spin–spin coupling. The powder spectrum also indicates that the absolute sign of 1J(31P,199Hg) is positive.

Unusual behaviour of the spin–spin coupling constant 1JCH upon formation of CH⋯X hydrogen bond

2020 ◽  
Vol 22 (4) ◽  
pp. 1994-2000
Author(s):  
Elena Yu. Tupikina ◽  
Gleb S. Denisov ◽  
Alexander S. Antonov ◽  
Peter M. Tolstoy
Keyword(s):  
Hydrogen Bond ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Interatomic Distances ◽  
Unusual Behaviour ◽  
Spin Spin Coupling

One-bond coupling constants 1JXY are usually used as a measure of the corresponding X⋯Y interatomic distances.

Long-range 13C, 13C spin–spin coupling constants in anisole and some derivatives

1988 ◽  
Vol 66 (7) ◽  
pp. 1635-1640 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Nuclear Magnetic

13C nuclear magnetic resonance chemical shifts and nJ(13C,13C) are reported for anisole and 16 of its derivatives, all enriched with 13C in the methoxyl group. 5J(13C,13C) is directly proportional to sin2θ, where θ is the angle by which the methoxy group twists about the C(1)—O bond. In acetone-d6 solution, 5J(C,C) is not observable for a number of 4-substituted anisoles, except for 1,4-dimethoxybenzene. For the latter, 5J(C,C) is compatible with a twofold barrier of 19.3 ± 1.1 kJ/mol hindering rotation about the C(1)—O bond. However, it is unlikely that the barrier is purely twofold in nature. The observed 5J(C,C) is also compatible with 10.5 and 6.0 kJ/mol for the twofold and fourfold components, respectively, implying a dynamical nuclear magnetic resonance barrier of less than 13 kJ/mol. While phase and solvent effects on the internal barrier in anisole are certainly substantial, it appears that a fourfold component must also be present. The apparent twofold barrier in 2,6-difluoroanisole is 5.4 ± 0.9 kJ/mol, based on 5J(C,C) and 6J(H-4,13C). The latter coupling constant is also reported for 1,2,3-trimethoxybenzene and used to deduce its conformation. The θ dependence of 3J(C,C) and 4J(C,C) is briefly discussed for symmetrical anisole derivatives. Differential 13C, 13C isotope shifts are reported for 1,4-dimethoxybenzene.

Long-range spin–spin coupling constants between ring protons and aldehydic protons in some para-substituted benzaldehydes

1969 ◽  
Vol 47 (21) ◽  
pp. 4005-4010 ◽  
Author(s):  
S. S. Danyluk ◽  
C. L. Bell ◽  
T. Schaefer
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Proton Proton ◽  
Proton Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Benzaldehyde Derivatives

The long-range proton–proton coupling constants between the ring protons and the aldehydic proton are reported for a series of para-substituted benzaldehyde derivatives. It was found that JoH,CHO < 0 and JmH,CHO > 0. Furthermore, JoH,CHO increases in magnitude as the electron donating power of the sub-stituent increases. A similar trend is observed forJmH,CHO but the ratio of the increase to the magnitude of JmH,CHO is much less than for JoH,CHO. A good correlation is obtained between JoH,CHO and the sub-stituent parameters of Swain and Lupton.The coupling constant data are discussed in terms of σ and π coupling mechanisms and it is concluded that σ electron mechanisms are dominant for both JoH,CHO and JmH,CHO.

C—H … O=C and C—H … H—C interactions in the side chains of 2-isopropylbenzaldehyde. A negative 5J(CHO,CH(CH3)2)

1991 ◽  
Vol 69 (6) ◽  
pp. 919-926 ◽  
Author(s):  
Ted Schaefer ◽  
Kerry J. Cox
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Aldehyde Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Side Chains ◽  
Hydrogen Atoms ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectra of 2-isopropylbenzaldehyde in CS2/C6D12 and acetone-d6 solutions provide the chemical shifts and coupling constants of all the protons. The long-range coupling constants involving the side-chain protons yield certain sums of the populations of the four putatively planar conformations. The o-anti conformers have a fractional population of 0.55(3) in the polar and of 0.49(3) in the nonpolar solvent. The conformers in which the methine C—H bond lies cis to the aldehyde group have a fractional population of 0.83(3) in both solutions. The close approach of the methine and aldehydic hydrogen atoms in one conformer is indicated by a negative proximate coupling constant between their protons of –0.39(1) Hz. The chemical shifts of the ring and of the side-chain protons are consistent with the conformer populations deduced from the long-range coupling constants and also with the indications that the side chains do not, on average, deviate from "coplanarity" with the ring by much more or less than in the parent compounds. The C—H … H—C and C—H … O=C interactions in the o-syn and o-anti conformers are most likely repulsive and of very similar magnitude and lead to a significant deshielding of the protons in these moieties. Molecular orbital computations are also reported and are an aid in estimating the populations of the individual conformers. The STO-3G MO structures have H … H and H … O distances well below the sums of the van der Waals radii of hydrogen and oxygen atoms in the conformers with the methine C—H bond placed cis to the aldehyde group, yet these are computed to be by far the most abundant by the STO-3G as well as by AM1 algorithms. Key words: 2-isopropylbenzaldehyde, conformations of; 2-isopropylbenzaldehyde, proximate spin–spin coupling constants in; MO calculations, STO-3G, and AM1 on 2-isopropylbenzaldehyde, 1H NMR and long-range spin–spin coupling constants in 2-isopropylbenzaldehyde.

The conformational behaviour of 2-fluoro and of 2,6-difluoroacetophenone implied by proximate spin–spin coupling constants and MO calculations

1985 ◽  
Vol 63 (8) ◽  
pp. 2256-2260 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Timothy A. Wildman ◽  
James Peeling
Keyword(s):  
Temperature Dependence ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Population Distributions ◽  
Carbon Carbon Bond ◽  
Acetyl Group ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The temperature dependence of [Formula: see text], the nuclear spin–spin coupling constant over five formal bonds between the methyl protons and the 19F nucleus in 2-fluoroacetophenone and 2,6-difluoroacetophenone, is modelled on the assumption that 5J is a proximate coupling and that the STO 3G MO potential functions describe the population distributions of the rotamers defined by rotation about the exocyclic sp2–sp2 carbon–carbon bond. It is assumed that 5J has a cos4 θ dependence between 0 and 90°, where θ is the angle by which the acetyl group twists out of the plane of the benzene plane. The potential function is obtained from extensive geometry optimization procedures for a range of θ values. At 305 K, nonplanar conformations are substantially populated in 2-fluoroacetophenone, according to this model, which is also consistent with the idea that the 2,6-difluoro derivative has a markedly nonplanar ground state. The model reproduces the large 5J in the monofluoro relative to the difluoro compound, as well as the much larger temperature dependence in the former.

Indirect Nuclear Spin-Spin Coupling Constants 1J(17O,13C) in Derivatives of Carbon Dioxide and Carbon Monoxide – Density Functional Theory (DFT) Calculations

2004 ◽  
Vol 59 (3) ◽  
pp. 286-290 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Carbon Dioxide ◽  
Density Functional Theory ◽  
Carbon Monoxide ◽  
Density Functional ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Calculations of spin-spin coupling constants 1J(17O,13C) in carbon dioxide (1) carbon monoxide (2) and several derivatives using density functional theory (DFT) have been carried out. This coupling constant possesses a positive sign [reduced coupling constant 1K(17O,13C)<0] except for the parent acylium cation [H-CO]+ (4a). It is shown that the Fermi contact term (FC) is positive [< 0 for 1K(17O,13C)] and that there are significant contributions from spin-dipole (SD) and paramagnetic spin-orbital (PSO) interactions

Signs of long-range amino proton – ring proton coupling constants in N-ethyl-4-chloro-2-nitroaniline

1970 ◽  
Vol 48 (8) ◽  
pp. 1343-1345 ◽  
Author(s):  
T. Schaefer ◽  
R. Wasylishen
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Proton Resonance ◽  
Ring Proton ◽  
Multiple Resonance ◽  
Proton Coupling ◽  
Spin Spin Coupling

In N-ethyl-4-chloro-2-nitroaniline there exists a measurable indirect spin–spin coupling constant of ±0.39 ± 0.03 Hz between the methylene protons and ring proton 6. The amino proton is coupled to ring protons 5 and 6 and also to the methylene protons. Consequently, although the amino proton resonance is broad due to incompletely relaxed coupling to 14N, normal multiple resonance experiments show that 5JmH,NH = 0.67 ± 0.03 Hz and 4JoH,NH = −0.35 ± 0.03 Hz.

A 13 C and 31 P magnetic double resonance study of organo-phosphorus compounds

1968 ◽  
Vol 306 (1485) ◽  
pp. 185-199 ◽  
Keyword(s):  
Phosphorus Atom ◽  
Chemical Shifts ◽  
Double Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Phosphorus Compounds ◽  
Resonance Spectroscopy ◽  
Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Twenty-two organo-phosphorus compounds of a variety of structural types have been examined by 1 H—{ 13 C} and 1 H—{ 31 P} magnetic double resonance spectroscopy. The signs and magnitudes of the 31 P—H and 31 P— 13 C spin-spin coupling constants are sensitive to the valency of the phosphorus atom, and the nature of the groups attached to it. Parallel behaviour is noted between two types of coupling constant. The 31 P chemical shifts agree with results obtained by conventional 31 P single resonance spectroscopy, and the 13 C chemical shifts depend on the polarizability of the phosphorus atom and its associated groups.

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