Long-range formyl proton coupling constants of 4-X-phenyl formats (X = H, F, CH3, NO2) and 2,6-dichlorophenyl formate. Conformations in solution

1988 ◽  
Vol 66 (8) ◽  
pp. 1787-1793 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Carbonyl Group ◽  
Long Range ◽  
Chemical Shifts ◽  
Aldehyde Group ◽  
Coupling Constants ◽  
Polar Solvents ◽  
Proton Coupling ◽  
Nitro Derivatives ◽  
Proton Chemical Shifts

The signs and magnitudes of the long-range coupling constants between the formyl and ring protons over five, six, seven, and eight bonds in phenyl formate and its 4-fluoro, 4-methyl, and 4-nitro derivatives are reported. These numbers are combined with CNDO/2 and INDO MO FPT computations of their conformational dependence and with STO-3G MO populational distributions to provide a description of the conformational behaviour of these molecules. The Z conformers, predominantly nonplanar and having the carbonyl group pointing towards the ring, appear to account for more than 95% of the molecules in CS2 solution at 300 K. In polar solvents, significant populations of the E conformers are indicated by the long-range coupling constants. The long-range coupling constants for the formyl proton in 2,6-dichlorophenyl formate are consistent with geometry-optimized STO-3G MO computations, which imply that the Z conformation, with the aldehyde group lying near the plane perpendicular to the benzene plane, is again at least 95% abundant at 300 K. The proton chemical shifts are also consistent with these conclusions.

The Molecular Structure of Allenes and Ketenes, XI Semiempirical Calculations of 1H-Chemical Shifts of Allenes

1977 ◽  
Vol 32 (11) ◽  
pp. 1296-1303 ◽  
Author(s):  
W. Runge
Keyword(s):  
Molecular Structure ◽  
Boundary Conditions ◽  
Chemical Shifts ◽  
Quantitative Description ◽  
Algebraic Model ◽  
Coupling Constants ◽  
Semiempirical Calculations ◽  
Proton Coupling ◽  
Nmr Data ◽  
Proton Chemical Shifts

A comparison between calculated and observed values demonstrates that “ansätze” derived from an algebraic model in connection with appropriate boundary conditions are able to account for a quantitative description of the proton chemical shifts of allenes.Correlations of the proton chemical shifts with other NMR data, such as 13C-chemical shifts and one-bond carbon-proton coupling constants, reveal some insigths into the nature of the 1H substituent chemical shifts of alienes.

Studies on the PMR Spectra of Oxetanes. VI 2-(3-Chlorophenyl)oxetane and 2-(2-Chlorophenyl)oxetane at 60 and 100 MHz

1974 ◽  
Vol 29 (12) ◽  
pp. 1902-1906 ◽  
Author(s):  
Jukka Jokisaari
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Methine Proton ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Proton Proton ◽  
Temperature Range ◽  
Proton Coupling ◽  
Phenyl Proton ◽  
Pmr Spectra

The 100 MHz spectra of the phenyl protons in 2-(3-chlorophenyl) oxetane and 2-(2-chlorophenyl) oxetane have been analysed. The 60 MHz PMR chemical shifts and proton-proton coupling constants have been studied in the temperature range from -20 C to +80 °C. The chemical shifts were sensitive to temperature, while the coupling constants were not, except the long range 5Jm coupling constant between the methine proton and the meta positioned phenyl proton in 2-(2-chlorophenyl) oxetane.

An 1H NMR conformational analysis of 3-phenylpentane in solution

1993 ◽  
Vol 71 (4) ◽  
pp. 520-525 ◽  
Author(s):  
Ted Schaefer ◽  
Lina B.-L. Lee
Keyword(s):  
Alkyl Chain ◽  
Chemical Shifts ◽  
Close Approach ◽  
Solvent Mixture ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Proton Proton ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Proton Chemical Shifts

Some 30 proton chemical shifts and proton–proton coupling constants are reported for a 4.7 mol% solution of 3-phenylpentane in a CS2/C6D12/TMS solvent mixture at 300 K. The long-range coupling constant over six formal bonds between the methine and para protons is used to deduce an apparent twofold barrier of 15.0 ± 0.3 kJ/mol to rotation about the Csp2—Csp3 bond, at least twice as large as that for isopropylbenzene in solution. AM1 computations agree with experiment in finding the conformation of lowest energy as that in which the methine C—H bond is situated in the phenyl plane, but predict a barrier height of only 13.9 kJ/mol. The vicinal coupling constants are consistent with a fractional population, 0.38(2), of the TT conformer, that in which all the carbon atoms of the alkyl chain lie in a plane. A doubly degenerate conformer, TG+(G−T), in which one methyl group is twisted away from the phenyl substituent, then has a fractional population of 0.62(2). The assumption that only these three conformers are present is tested with the signs and magnitudes of the four different coupling constants over four bonds. These coupling constants are consistent with the absence of significant proportions of the other six all-staggered conformers. These six are characterized by a close approach of the methyl groups (1,5 interactions) or by proximity of the methyl and phenyl moieties.

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.

Interpretation of cytidine proton chemical shifts and J coupling constants calculated by DFT

2006 ◽  
Vol 767 (1-3) ◽  
pp. 81-85 ◽  
Author(s):  
J.T. Fischer ◽  
S.G. Wehner ◽  
U.M. Reinscheid
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
J Coupling ◽  
J Coupling Constants ◽  
Proton Chemical Shifts

Assignment of carbon-13 NMR spectra and sign determination of long range carbon-13—proton coupling constants with SPI

1974 ◽  
Vol 6 (8) ◽  
pp. 445-447 ◽  
Author(s):  
A. A. Chalmers ◽  
K. G. R. Pachler ◽  
P. L. Wessels
Keyword(s):  
Long Range ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Proton Coupling ◽  
Sign Determination

Long-range couplings in the N.M.R. spectra of isoquinolines

1971 ◽  
Vol 24 (11) ◽  
pp. 2311 ◽  
Author(s):  
F Balkau ◽  
ML Heffernan
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants

The N.M.R. spectra of several isoquinolines have been recorded and analysed. Extensive spin-decoupling allowed the magnitudes and relative signs of the long- range coupling constants to be determined, and these are presented. Several unusual features of the chemical shifts and coupling constants are noted.

Concerning a relationship between long-range ring proton – methyl proton coupling constants and mobile bond order

1968 ◽  
Vol 46 (4) ◽  
pp. 654-656 ◽  
Author(s):  
D. J. Blears ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Linear Relationship ◽  
Long Range ◽  
Bond Order ◽  
Coupling Constants ◽  
Methyl Proton ◽  
Methyl Group ◽  
Potential Barriers ◽  
Proton Coupling ◽  
Induced Changes ◽  
Excitation Parameters

Long-range proton – methyl proton coupling constants in propene, mesitylene, 9-methylphenanthrene, and acenaphthene appear to be linearly related to the square of the mobile bond order between the carbon atoms bonded to the methyl group and the proton. However, substituent-induced changes in the charge on and hybridization state of the carbon atoms, in excitation parameters and in potential barriers to rotation of the methyl group, may also affect the coupling. Such changes must be considered in the application of a possible linear relationship.

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