Structure and bonding in cyclic phosphoramidates as determined by carbon-13 magnetic resonance

1979 ◽  
Vol 57 (1) ◽  
pp. 21-26 ◽  
Author(s):  
Gerald W. Buchanan ◽  
Frederick G. Morin
Keyword(s):  
Magnetic Resonance ◽  
Nitrogen Atom ◽  
Electron Pair ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Ring Conformation ◽  
Delocalized Electron ◽  
Nitrogen Lone Pair ◽  
Structure And Bonding

13C chemical shifts and 13C–31P couplings are reported for 11 cyclic phosphoramidates of ring sizes from four to nine. Vicinal couplings are compared with those of carbocyclic analogs and provide insight regarding the degree of nitrogen lone pair derealization into the N—P bond. For six-membered and larger rings, there appears to be nearly complete lone pair delocalization, i.e., a trigonal planar nitrogen atom. In azetidine derivatives the nitrogen lone pair remains localized, giving rise to a highly puckered ring conformation. Pyrrolidine derivatives are viewed as having a nitrogen with a partially delocalized electron pair.

N.M.R. spectra and stereochemistry of the bipyridyls. III. 2,2'-Bipyridyl and dimethyl derivatives, 3,3'- bipyridyl, and 4,4' - bipyridyl

1967 ◽  
Vol 20 (6) ◽  
pp. 1227 ◽  
Author(s):  
TM Spotswood ◽  
CI Tanzer
Keyword(s):  
Hydrogen Bonding ◽  
Electrostatic Field ◽  
Field Effect ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Diamagnetic Anisotropy ◽  
Equal Importance ◽  
Nitrogen Lone Pair ◽  
Lone Pair Electrons ◽  
Derivatives Of

The analysis of the n.m.r, spectra of 2,2?-, 3,3?-, and 4,4?-bipyridyl and three dimethyl-2,2?-bipyridyls is reported and the factors determining the relative chemical shifts of the ring protons and methyl groups in several solvents are discussed. The diamagnetic anisotropy of the neighbouring ring and electrostatic field effect of the nitrogen lone pair electrons are shown to be of roughly equal importance for derivatives of 2,2?-bipyridyl except in hydrogen bonding solvents. Attenuation of the electrostatic field effect in polar, and particularly in hydrogen bonding solvents, is established for 4- picoline, and for the bipyridyls, and this effect is responsible for striking changes in the spectrum of 2,2?-bipyridyl in hydrogen bonding solvents. An approximate interplanar angle of 58� is derived for 3,3?- dimethyl-2,2?-bipyridyl, and 2,2?-bipyridyl and its 4,4?- and 5,5?- dimethyl derivatives appear to be trans coplanar in all solvents. 3,3?- Bipyridyl and 4,4?-bipyridyl are probably highly twisted in all solvents, or alternatively, behave as essentially free rotors. The predicted conformations are in good agreement with the electronic spectral data.

Elektronendichte und chemische Verschiebung der Styryldiazin- und Diazaphenanthrenprotonen / Electrondensity and Proton Chemical Shift of Styryldiazines and Diazaphenanthrenes

1972 ◽  
Vol 27 (2) ◽  
pp. 310-319
Author(s):  
H.-H. Perkampus ◽  
Th. Bluhm ◽  
J. Knop
Keyword(s):  
Ring Current ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Current Effect ◽  
Electron Densities ◽  
Paramagnetic Effect ◽  
Nitrogen Lone Pair ◽  
Chemische Verschiebung ◽  
Lone Pair Electrons ◽  
Proton Chemical Shifts

AbstractProton chemical shifts in styryldiazines and diazaphenanthrenes linearly correlate with SCF-π-electron densities of the attached carbon atom and with the electron densities of the hydrogen atom (calculated by the CNDO/2 method). The observed deviations from linearity are discussed in terms of ring current effect, steric effects and the paramagnetic effect of the nitrogen lone pair electrons. An appreciable weakening of ring current is found for diazaphenanthrenes with two adjacent N-atoms. Under the same condition the paramagnetic effect on ortho-hydrogens is increased.

A nitrogen-15 nuclear magnetic resonance study of N-aryl phosphoramidates and phosphorimidates

1980 ◽  
Vol 58 (23) ◽  
pp. 2442-2446 ◽  
Author(s):  
G. W. Buchanan ◽  
F. G. Morin ◽  
R. R. Fraser
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Aromatic Ring ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Nuclear Magnetic Resonance Study ◽  
Magnetic Resonance Study ◽  
Nuclear Magnetic

15N nuclear magnetic resonance chemical shifts and one-bond 15N—31P couplings are reported for a series of five N-arylphosphoramidates and four N-arylphosphorimidates. Results are interpreted in terms of an extensively delocalized N lone pair in the phosphoramidates, with pπ–pπ donation into the aromatic ring being dominant over pπ–dπ donation from nitrogen to phosphorus.

Phosphorus-31 nuclear magnetic resonance spectra of methylplatinum(II) and methylpalladium(II) cations containing 4-substituted pyridine ligands

1979 ◽  
Vol 57 (9) ◽  
pp. 958-960 ◽  
Author(s):  
Howard C. Clark ◽  
Charles R. Milne
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Coupling Constants ◽  
The Other ◽  
Pyridine Ligands ◽  
Trans Influence ◽  
Nuclear Magnetic Resonance Spectra

The 31P nmr spectra of the compounds cis-[M(CH3)(L)diphos]PF6, where M = Pd, Pt; L = 4-C5H4NX; X = CH3, H, NMe2, COOMe, COMe, CN; diphos = 1,2-bisdiphenylphosphino ethane, have been recorded. The 31P chemical shifts and 31P–195Pt coupling constants decrease regularly as the ρ values of the substituent on pyridine decrease. These trends are attributed to decreasing lone pair donation from phosphorus as the electron donating ability of the other ligands on the metal increases. The trans influence of the coordinated pyridine molecule, as measured by J(195Pt–31P), is greater than its cis influence on the phosphorus atoms.

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.

scholarly journals A study of 13C–15N couplings and revised 13C shieldings in 15N-enriched E-acetophenone oximes

1976 ◽  
Vol 54 (5) ◽  
pp. 790-794 ◽  
Author(s):  
Gerald W. Buchanan ◽  
Brian A. Dawson
Keyword(s):  
Chemical Shifts ◽  
Lone Pair ◽  
Methoxyl Group ◽  
Coupling Constant ◽  
Absolute Value ◽  
Lanthanide Induced Shifts ◽  
Nitrogen Lone Pair ◽  
Acetophenone Oxime ◽  
Cndo Calculations ◽  
C Nmr

13C nmr chemical shifts and 13C–15N couplings through one, two, and three bonds are reported for E-acetophenone oxime and five para-substituted derivatives. It is shown that earlier assignments for three of these compounds, based on lanthanide induced shifts and CNDO calculations, are erroneous. With the exception of the methoxyl group, couplings are relatively insensitive to the nature of the para-function. For geminal 13C–15N interactions, the proximity of the nitrogen lone pair to the carbon terminus greatly enhances the absolute value of the coupling constant.

NUCLEAR MAGNETIC RESONANCE MEASUREMENTS IN SOLUTIONS OF ACETYLACETONE: THE EFFECT OF SOLVENT INTERACTIONS ON THE TAUTOMERIC EQUILIBRIUM

1957 ◽  
Vol 35 (11) ◽  
pp. 1351-1365 ◽  
Author(s):  
L. W. Reeves
Keyword(s):  
Chemical Shifts ◽  
Lone Pair ◽  
Tautomeric Equilibrium ◽  
Keto Form ◽  
Solvent Interaction ◽  
Solvent Interactions ◽  
Tautomeric Forms ◽  
Interacting Systems ◽  
Nitrogen Lone Pair ◽  
Hydrogen Bonded

A modified assignment of the PMR signals in acetylacetone is confirmed. The changes in intensity of selected signals with temperature are used to calculate an enthalpy of conversion of 2700 ± 100 cal. between keto and enol forms in pure acetylacetone.Interactions, which perturb the equilibrium between the tautomeric forms in dilute solution by formation of solution complexes, are studied by observing dilution chemical shifts in various solvents. The ratio of keto to enol forms is estimated from measurements of signal intensities at several dilutions in each solvent. The deviations from the correlations of Bernstein and Powling (5) between solvent dielectric constant and molar volume, and the position of the tautomeric equilibrium in dilute solutions, have been used as a criterion of solvent interaction. They are consistent with the present measurements.Typical basic, acidic, amphoteric, and neutral solvents have been chosen to investigate possible types of interaction. Cyclohexane and acetic acid do not perturb the equilibrium by any interactions. Triethylamine forms a hydrogen bonded complex through the enolic—OH group and the nitrogen lone pair, thus converting acetylacetone completely to enol form. Pyrrole forms a weakly hydrogen bonded complex through the carbonyl oxygens of the keto form. Freezing diagrams in the interacting systems are consistent with the complexes suggested by the PMR measurements.

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