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.

The Proton–Proton and Proton–Carbon-13 Spin–Spin Coupling Constants in 1,3-Dioxole and Bis-1,3-dioxolyl. Conformational Dependence

1975 ◽  
Vol 53 (18) ◽  
pp. 2734-2741 ◽  
Author(s):  
Ted Schaefer ◽  
Kalvin Chum ◽  
David McKinnon ◽  
M. S. Chauhan
Keyword(s):  
Double Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dihedral Angles ◽  
Proton Proton ◽  
Proton Coupling ◽  
Vicinal Proton ◽  
Karplus Relationship ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The carbon-13 satellite peaks in the proton magnetic resonance spectra of 1,3-dioxole and bis-1,3-dioxolyl are analyzed under single and double resonance conditions to yield the signs and magnitudes of proton–proton coupling constants over three, four, and five bonds, and of proton–carbon-13 coupling constants over one, two, and three bonds. The conformational behavior of bis-1,3-dioxolyl contrasts sharply with that of analogous sym-tetrasubstituted ethane derivatives. It is indicated that the two-bond proton–carbon-13 coupling in the ethanic fragment can be used for conformational analysis in a manner similar to vicinal proton–proton couplings. The vicinal three-bond proton–carbon-13 couplings are given for dihedral angles of 180 and 120° and their relative magnitudes are as expected from a Karplus relationship. The two-bond proton–carbon-13 coupling in the olefinic fragment is, at 20.0 Hz, the largest coupling known for such a bond.

The conformational distribution of 2-cyanobenzaldehyde and 3-cyanobenzaldehyde in solution and in the vapor

1991 ◽  
Vol 69 (7) ◽  
pp. 1039-1046 ◽  
Author(s):  
Ted Schaefer ◽  
Kerry J. Cox ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Dipole Moments ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Orbital Theory ◽  
Spectral Parameters ◽  
Proton Proton ◽  
H Nmr ◽  
Proton Coupling ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectra of 2-cyanobenzaldehyde (2CNB) and 3-cyanobenzaldehyde (3CNB) in CS2/C6D12 and acetone-d6 solutions at 300 K yield precise stereospecific long-range proton–proton coupling constants. These are used to establish the conformational population of the o-cis and o-trans conformers of these relatively polar molecules. For example, the fractional o-cis population of 2CNB changes from 0.12(4) in CS2/C6D12 to 0.46(6) in acetone-d6, whereas that of 3CNB is 0.48(2) in both solvents. Extrapolation to the vapor phase, using a dielectric model, implies a negligible concentration of the o-cis conformer of 2CNB and a roughly 50% abundance of each conformer of 3CNB. Computations at various levels of molecular orbital theory provide estimates of the rotational barrier of the aldehyde moiety and confirm the planar structure of each conformer. The geometries of three conformers are given as obtained from the 6-31G MO basis and may be useful to molecular spectroscopists. Theoretical and experimental dipole moments are interpolated to yield estimates of their magnitudes for the four planar conformers. Somewhat less precise 1H nmr spectral parameters (than for the above solutions) are also obtained for dilute solutions in benzene-d6 at 300 K. The conformational distributions based on these parameters are compared with their only other measurement, based on dipolar moments in benzene at 298 K. Good agreement between the results of the two methods is found for 3CNB but not for 2CNB. It is suggested that specific interactions occur between benzene solvent and solute molecules, particularly for 3CNB, for which these interactions stabilize the conformer having a low dipole moment. Remarkable changes in the intraring proton–proton coupling constants occur in going from CS2/C6D12 to acetone-d6 solution. Key words: 2- and 3-cyanobenzaldehyde (2CNB and 3CNB): 1H NMR, conformations, long-range spin–spin coupling constants, MO computations.

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.

Indirekte Kernspinkopplung in den Tetramethylverbindungen der IV. Gruppe

1967 ◽  
Vol 22 (9) ◽  
pp. 1458-1464 ◽  
Author(s):  
Herbert Dreeskamp ◽  
Gerhard Stegmeier
Keyword(s):  
Double Resonance ◽  
Group Iv ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Group Iv Elements ◽  
Semi Empirical ◽  
Spin Spin Coupling ◽  
Contact Mechanism ◽  
Good Agreement

The indirect nuclear spin-spin coupling between protons, C13 and the spin ½ isotopes of the group IV elements (Si29, Sn119 and Pb207) were investigated in the tetramethylcompounds X(CH3)4. Substances enriched in C13 were used. The absorption of the most sensitive nucleus H1 was observed directly while the resonances of the other nuclei were located by a double resonance technique. The normalized coupling constants between directly bonded nuclei were found to be positive in all cases while their magnitudes are in good agreement with a semi-empirical estimate using the contact mechanism. All normalized two-bond X—C—H coupling constants are negative while the three-bond C—X—C—H coupling constants are positive as well as the four-bond H—C—Si—C—H coupling constant. Using these results it is shown that the sign of the normalized X—H coupling constants in the analogous hydrides XH4 are positive confirming a theoretical prediction made in previous work.

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.

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.

scholarly journals Signs of proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine. Sigma and pi contributions to coupling in a nitrogen heterocycle

1969 ◽  
Vol 47 (9) ◽  
pp. 1507-1514 ◽  
Author(s):  
T. Schaefer ◽  
S. S. Danyluk ◽  
C. L. Bell
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nitrogen Heterocycle ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Proton Proton ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The signs of all proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine have been determined by double and triple resonance experiments. The signs of the longrange coupling constants, JH,CH3 and JF,CH3 are the same as in fluorotoluene derivatives. Their magnitudes are consistent with the assumption that the nitrogen atom primarily polarizes the σ bonds in the molecule, leaving the π contribution to the long-range coupling relatively unaffected.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

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