Geminal H,D spin-spin coupling and isotope effects in partially deuterated methyl-aromatic compounds

1964 ◽  
Vol 17 (1) ◽  
pp. 38 ◽  
Author(s):  
CG Macdonald ◽  
JS Shannon ◽  
S Sternhell
Keyword(s):  
Aromatic Compounds ◽  
Hydrogen Exchange ◽  
Isotope Effects ◽  
Deuterium Atom ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Deuterium Isotope Effect ◽  
Methyl Group ◽  
Catalytic Hydrogen ◽  
Spin Spin Coupling

Seventeen methyl-aromatic compounds were selectively, partially deuterated by catalytic hydrogen exchange. The proton magnetic resonance (p.m.r.) spectra of the partially deuterated compounds showed that the geminal H,D coupling constant is approximately 2.2 c/s and that it does not vary significantly with the type of substitution in the ring. The deuterium isotope effect on the chemical shift of the remaining protons in the methyl group is approximately 0.7-1.1 c/s in the upfield direction for the introduction of one deuterium atom.

The probable planarity of 1,2-dimethoxybenzene in solution

1983 ◽  
Vol 61 (2) ◽  
pp. 224-229 ◽  
Author(s):  
Ted Schaefer ◽  
Reino Laatikainen
Keyword(s):  
Benzene Solution ◽  
Theoretical Data ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Nmr Spectrum ◽  
Methyl Group ◽  
H Nmr ◽  
Planar Conformation ◽  
Precise Analysis ◽  
Spin Spin Coupling

A precise analysis of the 1H nmr spectrum of 1,2-dimethoxybenzene in benzene solution yields an accurate value for the proximate spin–spin coupling constant, [Formula: see text], between the ortho ring proton and the methyl protons. The latter also couple to other ring protons and these couplings are assessed. Comparison with some values in other anisole derivatives and with a variety of INDO MO FPT calculations of [Formula: see text] strongly implies the predominance of a planar conformation in solution. This implication disagrees with the interpretation of some other experimental and theoretical data. The mechanism of this proximate coupling is examined by the procedure of Barfield. It seems that the magnitude of the coupling is dominated by interactions involving the orbitals on the carbon atom of the methyl group.

The range of in anisole derivatives. An indicator of torsion and compression of the methoxy group

1985 ◽  
Vol 63 (3) ◽  
pp. 782-786 ◽  
Author(s):  
Ted Schaefer ◽  
Salman R. Salman ◽  
Timothy A. Wildman ◽  
Glenn H. Penner
Keyword(s):  
Methoxy Group ◽  
Bond Angle ◽  
Average Distance ◽  
Electron Donors ◽  
Spin Coupling ◽  
Ortho Position ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Methyl Group ◽  
Spin Spin Coupling

In a series of anisole derivatives, [Formula: see text], the spin–spin coupling constant between the methyl protons and the ring proton in the ortho position, ranges from −0.23 to −0.38 Hz when the methyl group lies cis to the ortho C—H bond. 5J, as a proximate coupling, is sensitive to the average distance between the coupled protons. Its variation with substituent can be rationalized in terms of torsion about the Csp2—O bond and changes in the bond angles near the methoxy moiety. The theoretical 5J numbers can be empirically reproduced by a cos4 ψ function, where ψ is the angle by which the methoxy group twists out of the benzene plane. In general, large ortho substituents cause an increase in the magnitude of 5J (bond angle changes), strong π electron donors in the para position cause a decrease in the magnitude of 5J (increased torsional freedom), and π electron acceptors do the opposite (decreased torsions).

Indirekte Kernspinkopplung zwischen Protonen und Elementen der IV. Gruppe

1964 ◽  
Vol 19 (1) ◽  
pp. 139-142 ◽  
Author(s):  
Herbert Dreeskamp
Keyword(s):  
Electron Density ◽  
Strong Correlation ◽  
Valence Electron ◽  
Spin Coupling ◽  
Atomic Data ◽  
Coupling Constant ◽  
Methyl Group ◽  
Hartree Fock ◽  
Fermi Contact ◽  
Spin Spin Coupling

The indirect spin-spin coupling between protons and Ge73, spin 9/2, in the tetraedric molecule GeH4 has been measured. JGe-H = 97,6 Hz. Introducing the normalized coupling constant J′ which is obtained by dividing the measured coupling constant by the product of the magnetogyric ratios of the coupling nuclei, a strong correlation is found between this quantity for XH4 (X = C, Si, Ge, Sn, Pb) and the electron density of the valence electron at the nucleus obtained from HARTREE-FOCK calculations or experimental atomic data. This demonstrates that at least in these cases the FERMI contact contribution is dominant. For the analogeous tetramethyl compounds the same relation holds only to the extend that the C - H coupling in the methyl group is constant.

The sign of the 'through-space' spin–spin coupling between methyl protons and the fluorine nucleus in 2,6-dimethylbenzoyl fluoride

1976 ◽  
Vol 54 (5) ◽  
pp. 800-804 ◽  
Author(s):  
Ted Schaefer ◽  
Kalvin Chum ◽  
Kirk Marat ◽  
Roderick E. Wasylishen
Keyword(s):  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Fluorine Nucleus ◽  
Methyl Group ◽  
Out Of Plane ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Carbonyl Fluoride

The spin–spin coupling constant over five formal bonds between 19F and methyl protons, [Formula: see text], in 2,6-dimethylbenzoyl fluoride is −3.1 Hz. Observation of a nonzero [Formula: see text] indicates an out-of-plane conformation for the carbonyl fluoride group and implies substantial nonbonded repulsions between the methyl and carbonyl fluoride groups. It is argued that [Formula: see text] is as small as −7 Hz when the C—F bond lies cis to a methyl group and that its magnitude is a consequence of the so-called 'through-space' coupling mechanisms. On the basis of INDO–MO–FPT computations, it is suggested that such observed couplings are a composite of large contributions of either sign and, therefore, that observed through-space 1H,19F couplings may be of either sign if conformational averaging occurs.

31P−15N Coupling Constants and 15N/14N Isotope Effects on 31P NMR Chemical Shifts of 2-Phenylamino-2-oxo(-thioxo, -selenoxo)- 4-methyl-1,3,2-dioxaphosphorinanes and Related Compounds

1983 ◽  
Vol 38 (7) ◽  
pp. 815-818 ◽  
Author(s):  
Willy Gombler ◽  
Ryszard W. Kinas ◽  
Wojciech J. Stec
Keyword(s):  
31P Nmr ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
The Family ◽  
Nuclear Shielding ◽  
Spin Spin Coupling ◽  
Related Compounds

The strong influence of a chalcogen atom (O, S, Se) attached to phosphorus on the spin-spin coupling constant 1J(P-15N) in the family of diastereoisomeric 2-|15N] -phenyl-amino-2X(X = O, S, Se)-4-methyl-l,3,2-dioxaphosphorinanes is demonstrated. The 15N/14N isotope effect on the nuclear shielding of phosphorus-31 is larger for the shorter equatorial than for the longer axial P-N bonds.

The proximate coupling constant, 5J(H,CH3), and the torsional mobility of the thiomethyl group in some thioanisole derivatives

1991 ◽  
Vol 69 (4) ◽  
pp. 620-624 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Salman R. Salman ◽  
James D. Baleja ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Bond Order ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Torsional Motion ◽  
Coupling Constant ◽  
Methyl Group ◽  
H Nmr ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Ortho Substituent

The proximate coupling constants, 5J, between ortho and methyl protons in thioanisole and 18 of its derivatives are discussed as conformational indicators. On the assumption that 5J varies as cos4θ, for 0° ≤ θ ≤ 90°, θ being the angle by which the methyl group twists out of the aromatic plane, 5J for θ = 0° follows as −0.43 (2) Hz from the known internal barrier in thioanisole in solution. A measurement of 5J in meta- or para-substituted thioanisole derivatives then yields an approximate value for the twofold barrier to rotation about the Csp2—S bond. For derivatives containing an ortho substituent, 5J yields an estimate of the torsion angle for the thiomethyl moiety. In some instances these angles are compared with those derived from long-range 1H, 13C and 13C, 13C coupling constants. The size of the ortho substituent appears to have only a small effect on the magnitude of 5J. The major determinant of the latter appears to be the manner in which the substituent perturbs the mobile bond order of the Csp2—S bond. Key words: spin–spin coupling constants, thioanisole derivatives; 1H NMR, thioanisole derivatives; conformations, thioanisole derivatives; conformations, torsional motion of SCH3 group.

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.

Internal motion in benzylidene diacetate and its 2,6-dibromo derivative by DNMR and the J method

1989 ◽  
Vol 67 (6) ◽  
pp. 1022-1026 ◽  
Author(s):  
Ted Schaefer ◽  
Craig S. Takeguchi
Keyword(s):  
Double Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Maximum Magnitude ◽  
Coupling Constant ◽  
Spectral Parameters ◽  
Proton Proton ◽  
Ether Solution ◽  
Spin Spin Coupling ◽  
Dibromo Derivative

The 1H nuclear magnetic resonance spectral parameters are reported for benzylidene diacetate in CS2 and acetone-d6 solutions. The long-range spin–spin coupling constant over six formal bonds, 6J, is used to derive apparent twofold barriers to rotation about the exocyclic C(1)—C bond in the two solutions. The conformation of lowest energy has the α. C—H bond in the benzene plane. The barrier is higher in CS2 than in acetone-d6 solution, in contrast to a molecule like benzyl chloride. In the 2,6-dibromo derivative, the free energy of activation for reorientation about the bond in question is 36 kJ/mol at 165 K in dimethyl ether solution. Such a high barrier implies a very small six-bond proton–proton coupling constant for this derivative because 6J is proportional to the expectation value of sin2θ. The angle θ is zero when the α C—H bond lies in the benzene plane. 6J is −0.051 Hz in acetone-d6 solutions; its sign is determined by double resonance experiments. The question of an angle-independent component of 6J, that is, whether 6J is finite at θ = 0°, is addressed. A maximum magnitude of 0.02 Hz may be present at θ = 0° for the 2,6-dibromo derivative, although a zero magnitude is also compatible with the experimental data. In a compound with a higher internal barrier, α,α,2,6-tetrachlorotoluene, the experimental results are best in accord with a negligibly small 6J at θ = 0°. Keywords: 1H NMR of benzylidene diacetate, spin–spin coupling constants for benzylidene diacetate, DNMR, 2,6-dibromobenzylidene diacetate.

"Through-space" spin–spin coupling between thallium and fluorine in fluorophenylthallium compounds

1989 ◽  
Vol 67 (11) ◽  
pp. 1847-1850
Author(s):  
Gerald Norman Pecksen ◽  
Raymond Frederick Martin White
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Methyl Group ◽  
Fluorine Nmr ◽  
Thallium Atom ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Thallium to fluorine spin–spin coupling constants have been measured for a number of fluoro- and trifluoro-methyl-substituted mono- and di-arylthallium derivatives. The results provide evidence of "through-space" coupling in the diaryl derivatives when the fluoro- or trifluoro-methyl group is ortho to the thallium atom. Keywords: thallium, fluorine, NMR, through-space coupling.

Sign in / Sign up

Export Citation Format

Share Document