The mechanisms of long-range 13C,19F and 19F,19F coupling constants in derivatives of biphenyl and fluorene. Differential isotope shifts

1986 ◽  
Vol 64 (11) ◽  
pp. 2162-2167 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Glenn H. Penner
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Diffraction Patterns ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Coupling Components

13C,19F and 19F,19F nuclear spin–spin coupling constants over n formal bonds, n = 1–9, are reported for 4-fluorobiphenyl, 4,4′-difluorobiphenyl, 4,4′-difluoro-2,2′,6,6′-tetramethylbiphenyl, 2,7-difluorofluorene, 2-fluoro-9-fluorenone, and 2,7-difluoro-9-fluorenone in acetone solutions. The signs of many of the coupling constants are deduced from second-order spectral phenomena caused by differential 13C isotope effects on the I9F nmr chemical shifts. Theoretical potentials, based on geometry-optimized STO 3G MO computations for 4-fluorobiphenyl and 4,4′-difluorobiphenyl, yield expectation values for the torsion angles about the exocyclic C—C linkage that are very close to those deduced from electron diffraction patterns. These potentials and INDO MO FPT computations of the long-range coupling constants allow a discussion of the coupling mechanisms. In Hz, 9J(F,F) = 1.3(1) cos2 θ, where θ is zero for a planar biphenyl, while 8J(C,F) = 0.8(1) cos2 θ and 7J(C,F) = −0.43(5) cos2 θ. 6J(C,F) is a composite of σ–π and π electron coupling components and is written in Hz as 0.57(1) + 0.29(1) sin2 θ. The corresponding coupling constants in the fluorene and 9-fluorenone derivatives are enhanced in magnitude relative to a hypothetical planar biphenyl derivative. It is tentatively suggested that 5J(C,F) consists of three coupling components, one negative and proportional to cos2 θ, the other two positive and independent of θ. 4J(C,F) is suggested to consist of a σ component of −1.0 Hz and a π component proportional to the atom–atom polarizability for the parent hydrocarbon.

13C, 1H-Spin-Spin Kopplungskonstanten, Teil IVAdamantan / 13C, 1H Spin-Spin Coupling Constants, Part IVAdamantane

1979 ◽  
Vol 34 (3) ◽  
pp. 528-529 ◽  
Author(s):  
Rafet Aydin ◽  
Harald Günther
Keyword(s):  
Chemical Shifts ◽  
Isotope Effects ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Substitution Pattern ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Abstract One-bond, geminal, and vicinal 13C, 1H coupling constants have been determined for adamantane using α-and β-[D]adamantane and the relation nJp(13C, 1H) = 6,5144 nJ(13C, 2H) for the conversion of the measured nJ(13C, 2H) values. It is shown that the magnitude of 3Jtrans is strongly influenced by the substitution pattern. Relative H,D isotope effects for 13C chemical shifts are given.

Long-range proton–19F spin–spin coupling interactions in phenyltrifluorosilane

1977 ◽  
Vol 55 (18) ◽  
pp. 3243-3247 ◽  
Author(s):  
William J. E. Parr ◽  
T. Schaefer ◽  
K. Marat
Keyword(s):  
Long Range ◽  
Resonance Spectrum ◽  
Base Point ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hindered Rotation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

Analysis of the proton magnetic resonance spectrum of phenyltrifluorosilane yields the spin–spin coupling constants between the fluorine nuclei and the protons. These are compared with the analogous long-range coupling constants in benzotrifluoride, toluene, and phenylsilane and are rationalized in terms of coupling mechanisms. The coupling over six bonds is assessed as a base point for the estimation of hindered rotation about the carbon–silicon bond.

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.

Long-range proton-fluorine spin-spin coupling and 19F substituent chemical shifts (SCS) in the naphthalene ring system

1971 ◽  
Vol 24 (9) ◽  
pp. 1829 ◽  
Author(s):  
W Adcock ◽  
DG Matthews ◽  
SQA Rizvi
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Naphthalene Ring ◽  
Methyl Proton ◽  
Direct Mechanism ◽  
Spin Coupling Constants ◽  
Proton Resonances ◽  
Spin Spin Coupling

A number of acetyl-substituted fluoronaphthalenes have been synthesized and their fluorine as well as proton N.M.R. spectra have been measured. The methyl proton resonances of these derivatives appeared as a doublet which indicated long-range coupling with the fluorine. It was observed that the coupling (JMe,F) for 3-acetyl-2-fluoronaphthalene and o- fluoroacetophenone is independent of the magnitude of the 19F substituent chemical shifts (scs) which are shown to be sensitive indices of the bond-order differences in naphthalene (C 1 and C 2; C 2 and C 3) and benzene. Furthermore, the magnitude of the long-range proton-fluorine spin-spin coupling constants are solvent dependent. The data are clearly in accord with a predominant contribution of a ?direct? mechanism to the proton-fluorine spin-spin coupling.

Proton Spin–Spin Coupling Constants in Isothiazole, Isoxazole, and some of their Alkyl Derivatives

1974 ◽  
Vol 52 (5) ◽  
pp. 833-837 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
J. Brian Rowbotham ◽  
Ted Schaefer
Keyword(s):  
Chemical Shifts ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Common Mechanism ◽  
Orbital Theory ◽  
Alkyl Derivatives ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

The signs and magnitudes of the spin–spin coupling constants over three to six bonds between protons in isothiazole, isoxazole, and in 10 of their alkyl derivatives are measured and discussed in terms of the coupling mechanisms. The chemical shifts of ring protons and methyl protons appear to arise from a common mechanism originating in the ring but are not simply related to electron densities calculated by molecular orbital theory at the CNDO/2 level of approximation.

scholarly journals A relationship between some long-range 2H/1H isotope shifts in 13C nuclear magnetic resonance and long-range spin–spin coupling constants for toluene, ethylbenzene, and isopropylbenzene

1983 ◽  
Vol 61 (12) ◽  
pp. 2777-2778 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Timothy A. Wildman
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ring Plane ◽  
Expectation Value ◽  
Deuterium Substitution ◽  
13C Nuclear Magnetic Resonance ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

A very good correlation exists between long-range spin–spin coupling constants involving the α-protons in toluene, ethylbenzene, and cumene, and the changes in the chemical shifts of the para and α carbons caused by deuterium substitution at the α carbon. The coupling constants depend on sin2 θ, where θ is the angle by which the α C—H bond twists out of the ring plane, and can be used to find the expectation value of sin2 θ. Consequently the observed correlation provides quantitative support for the hyperconjugative model employed by Wesener and Günther.

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

Sign in / Sign up

Export Citation Format

Share Document