1H and 13C nuclear magnetic resonance studies of the conformational equilibrium of 2-(diphenylphosphino)benzaldehyde in polar and nonpolar solutions. Signs of the proximate coupling constants, 4J(CHO, 31P) and 3(13CHO, 31P)

1993 ◽  
Vol 71 (9) ◽  
pp. 1384-1393 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Robert W. Schurko ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Lone Pair ◽  
Pair Interaction ◽  
Coupling Constants ◽  
Torsion Angles ◽  
Solvent Dependence ◽  
13C Nuclear Magnetic Resonance ◽  
Repulsive Forces ◽  
Nuclear Magnetic

The analyses of the 1H nuclear magnetic resonance spectra of 2-(diphenylphosphino)benzaldehyde in CS2/C6D12 and acetone-d6 solutions yield stereospecific coupling constants from which the populations of the O-cis and O-trans conformers are derived. The free energy differences favouring the O-trans conformer at 300 K are 2.7 and 0.9 kJ/mol, in the polar and nonpolar solutions, respectively; in the crystal only the O-cis conformer exists. The coupling constant, 4J(CHO, P), is estimated as −7.1(2) Hz in the O-trans confomer and 3J(CHO, P) as +29.4(1.3) Hz. Their magnitudes depend on the proximity of the C—H bond to the lone pair on phosphorus. nJ(C, P) are reported for triphenylphosphine and for the benzaldehyde derivative as dilute solutions in the two solvents, demonstrating a significant solvent dependence for some of these coupling constants. Some simple relationships are proposed between nJ(C, P) and the torsion angle about the C—P bond, estimates of the latter coming from AM1 and STO 3G MO computations. nJ(C, P) are also sensitive to intrinsic ring substituent perturbations, as are the nJ(H, P); for example, 5J(H, P) is negative in the disubstituted ring of 2-(diphenylphosphino)benzaldehyde but positive in the phenyl groups. The nJ(H, P) are also discussed with respect to their dependence on the torsion angles about the C—P bonds. It appears that the conformational properties of the aromatic rings in triphenylphosphine and its formyl derivative are very similar. Further, the phosphorus atom is polarized such that the carbonyl bond is attracted towards the positive region near phosphorus, and the C—H bond of the formyl group more towards the lone-pair region; the actual torsion angles represent a compromise between these attractive forces and the repulsive forces between bonds on neighbouring aromatic moieties. CNDO/2 MO and INDO MO FPT computations of nJ(C, P) and nJ(H, P) are of mixed utility, although the former bear out the idea that the proximate [Formula: see text]lone-pair interaction dominates 3J(CHO,P) and 4J(CHO,P).

13C nuclear magnetic resonance spectra of 3,6-disubstituted pyridazines

1991 ◽  
Vol 69 (6) ◽  
pp. 972-977 ◽  
Author(s):  
Gottfried Heinisch ◽  
Wolfgang Holzer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

The 13C nuclear magnetic resonance spectra of 17 3,6-disubstituted pyridazine derivatives have been systematically analyzed. Chemical shifts and various 13C, 1H coupling constants are reported. Attempts were made to correlate these data with results obtained from semiempirical molecular orbital calculations as well as with substituent electronegativities and Taft's substituent constants σI and σR0. Key words: 3,6-disubstituted pyridazines, 13C NMR spectroscopy, 13C, 1H spin coupling constants.

A 1H and 13C nuclear magnetic resonance study of nucleosides with methylated pyrimidine bases

1982 ◽  
Vol 60 (24) ◽  
pp. 3026-3032 ◽  
Author(s):  
Frank E. Hruska ◽  
Wayne J. P. Blonski
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Coupling Constants ◽  
Magnetic Resonance Data ◽  
Proton Coupling ◽  
13C Nuclear Magnetic Resonance ◽  
Pyrimidine Bases ◽  
Nuclear Magnetic

Alkylated pyrimidine bases are of interest from the viewpoint of mutagenesis and carcinogenesis. 1H nuclear magnetic resonance data are presented for a series of ribosides and arabinosides alkylated at the O2,O4, N3, and C5 positions of the pyrimidine base. The data provide information about the stereochemical effects of base methylation. The J(5—6) proton coupling constants show that O-alkylation leads to a decrease in the π-bond order of the C5—C6 bond. The 13C chemical shifts are related to the tautomeric changes effected by O-alkylation.

39K and 13C nuclear magnetic resonance studies of the potassium cation – dibenzo-30-crown-10 complex in solution

1987 ◽  
Vol 65 (7) ◽  
pp. 1684-1687 ◽  
Author(s):  
Christian Detellier ◽  
Marc Robillard
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Times ◽  
Potassium Thiocyanate ◽  
Coupling Constants ◽  
Potassium Cation ◽  
Thiocyanate Complex ◽  
Quadrupolar Coupling ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The structure and microdynamics in solution of the dibenzo-30-crown-10–potassium thiocyanate complex have been studied by 39K and 13C nuclear magnetic resonance. In the four solvents studied (nitromethane, acetonitrile, acetone, and pyridine), the large crown ether wraps around the potassium cation and expels the conjugate anion and the solvent molecules from the cation coordination sphere. Measurements of 39K quadrupolar and 13C dipole–dipole relaxation times in acetone-d6 gave the effective correlation time of the complex and the 39K quadrupolar coupling constant (1.4 ± 0.3 MHz). The comparison between 23Na and 39K quadrupolar coupling constants for the complexes Na+–dibenzo-24-crown-8 and K+–dibenzo-30-crown-10 showed that the electric field gradients at the metal nucleus sites are quasi identical [Formula: see text] in the two complexes.

Structural elucidation of the capsular polysaccharide antigen of Neisseria meningitidis serogroup Z using 13C nuclear magnetic resonance

1979 ◽  
Vol 57 (22) ◽  
pp. 2902-2907 ◽  
Author(s):  
Harold J. Jennings ◽  
Karl-Gunnar Rosell ◽  
C. Paul Kenny
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Neisseria Meningitidis ◽  
Capsular Polysaccharide ◽  
Resonance Spectrum ◽  
Coupling Constants ◽  
Polysaccharide Antigen ◽  
Phosphate Diester ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The capsular polysaccharide antigen from Neisseriameningitidis serogroup Z contains equimolar quantities of 2-acetamido-2-deoxy-D-galactose, glycerol, and phosphate. Carbon-13 nuclear magnetic resonance indicates that the polysaccharide is composed by a repeating unit of 1′-O-2-acetamido-2-deoxy-α-D-galactopyranosyl-glycerol joined through phosphate diester groups at O-3′ of glycerol and O-3 of the galactosamine residue. Assignments of the signals in the carbon-13 nuclear magnetic resonance spectrum were made by consideration of the previously assigned signals of related monomers and oligomers. When applied to a Karplus type relationship the values of the 3J(13C–31P) coupling constants were consistent with the polysaccharide having an extended conformation.

A precise analysis of the 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane. Ring pucker, signs of long-range J(H,H), internal rotational barrier, and van der Waals shifts

1994 ◽  
Vol 72 (7) ◽  
pp. 1722-1727 ◽  
Author(s):  
Ted Schaefer ◽  
Jeremy P. Kunkel ◽  
Robert W. Schurko ◽  
Guy M. Bernard
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrum ◽  
Resonance Spectrum ◽  
Chemical Shifts ◽  
Van Der Waals ◽  
Lone Pair ◽  
Coupling Constants ◽  
Van Der Waals Interactions ◽  
Nuclear Magnetic

The 1H nuclear magnetic resonance spectrum of 2-phenyl-1,3-dithiane, as a dilute solution in a CS2–C6D12–TMS solvent mixture at 300 K, is analyzed to yield 8 chemical shifts and 22 distinct coupling constants, nJ(H,H), n = 2–6. The coupling constant between H-2 and the para proton indicates, first, that the bisected conformer (phenyl plane perpendicular to the pseudo plane of the dithiane ring) is most stable and, second, that the apparent twofold barrier to rotation about the Csp2—Csp3 bond is 9.6 kJ/mol. The AM1, STO-3G, and STO-3G* computations confirm the twofoldedness of the barrier; the AM1 barrier is 9.4 kJ/mol. The empirical equation, [Formula: see text] reproduces the vicinal coupling constants of the CH2CH2CH2 fragments and implies puckering angles [Formula: see text] of 54°, 61°, and 64°, respectively. It is implied that 3J at [Formula: see text] is larger than at [Formula: see text] This results is discussed in terms of the latest theoretical approach to 3J in the HCCH fragment. The 4J(H,H) signs and magnitudes for the CH2CH2CH2 fragment agree reasonably well with theory. For the CH2SCH fragment, 4J(H,H) values are positive, in contrast to corresponding numbers in the propanic fragment, perhaps the first experimental values for certain rigid orientations about a heteroatom. INDO MO FPT computations on propane, dimethyl ether, and dimethyl sulfide confirm the experimental trend in 4J(H,H). 2J(H,H) and 5J(H,H) values are compared to those in related molecules. The striking differential shifts of the axial and equatorial protons are attributed to differential van der Waals interactions with the 3p lone-pair orbital on sulfur. A comparison of the ring proton chemical shifts with those in phenylcyclohexane and isopropylbenzene implies that C—S bonds are weaker net electron donors by hyperconjugation than are C—C bonds. It is also proposed that the ortho protons are deshielded by intramolecular van der Waals interactions with the 3p orbitals on the sulfur atoms.

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