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.

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.

Liaison hydrogène des arylamines : compétition des sites π et N

2004 ◽  
Vol 82 (9) ◽  
pp. 1413-1422 ◽  
Author(s):  
Eric Marquis ◽  
Jérôme Graton ◽  
Michel Berthelot ◽  
Aurélien Planchat ◽  
Christian Laurence
Keyword(s):  
Hydrogen Bonding ◽  
Lone Pair ◽  
Molecular Electrostatic Potentials ◽  
Hydrogen Bond Donor ◽  
Complexation Constant ◽  
Steric Factors ◽  
Troger's Base ◽  
Nitrogen Lone Pair ◽  
Ir Study ◽  
Hydrogen Bonded

An IR study, in the region of OH stretching, of a reference hydrogen-bond donor, 4-fluorophenol, hydrogen bonded to primary, secondary, and tertiary arylamines differently substituted on the ring and on the nitrogen, shows the formation of two kinds of 1:1 complexes in CCl4 solution: an OH···π and an OH···N hydrogen-bonded complex. The IR method gives only access to a global complexation constant Kt. A method is proposed for separating Kt into a Kπ component for hydrogen bonding to the π system and a KN component for hydrogen bonding to the nitrogen atom. This method is validated by comparing the estimated Kπ and KN values to theoretically calculated descriptors of basicity: the nitrogen lone pair orientation towards the aromatic ring, the molecular electrostatic potentials around the nitrogen and the π cloud, and the enthalpy of hydrogen bonding of hydrogen fluoride with the π system of selected arylamines. The main electronic and steric factors governing the competition between π and N sites are analysed. The strongest π and N bases among the arylamines are julolidine and Tröger's base, respectively. Triphenylamine and diphenylamine, which are nitrogen Brønsted bases, become π bases in hydrogen bonding. Moreover, there is no correlation between the pKHB and the pKBH+ scales of basicity of arylamines. The use of the pKBH+ scale is therefore not recommended in hydrogen-bonding studies.Key words: hydrogen bonding, arylamines, pKHB scale, competition of π and N hydrogen-bonded sites.

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.

13C NMR spectroscopic studies of C-nitroso compounds. The orientation of the nitroso group in substituted nitrosobenzenes

1994 ◽  
Vol 72 (3) ◽  
pp. 514-518 ◽  
Author(s):  
Brian G. Gowenlock ◽  
Mailer Cameron ◽  
Alan S.F. Boyd ◽  
Baheeja M. Al-Tahou ◽  
Paul McKenna
Keyword(s):  
Solid State ◽  
Functional Group ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Spectroscopic Studies ◽  
Nitroso Compounds ◽  
Nitroso Group ◽  
Nitrogen Lone Pair ◽  
Electronic Character ◽  
Ortho Substituent

The carbon-13 chemical shifts of several substituted nitrosobenzenes are reported. It is shown that the NO group can be orientated to lie in the plane of the ring when constrained either by a bulky ortho substituent or in the solid state. In the presence of 2,6-di-tert-butyl substituents the NO group is twisted into orthogonality with the ring. The changes in the 13C chemical shifts are larger for the NO group than for other functional groups. It is suggested that these effects are a consequence of the electronic character of the NO group and that the nitrogen lone pair of electrons is of fundamental importance in producing these unique effects. The dimeric nitroso functional group does not display these properties.

A study of lone-pair interactions of tetracyclic diamines by ultraviolet photoelectron spectroscopy

1986 ◽  
Vol 64 (4) ◽  
pp. 760-763 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Douglas Neve Butler ◽  
Sushil Datta
Keyword(s):  
Photoelectron Spectroscopy ◽  
Lone Pair ◽  
Photoelectron Spectra ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
First Report ◽  
Lone Pairs ◽  
Nitrogen Lone Pair ◽  
Lone Pair Interactions ◽  
Pair Interactions ◽  
Hydrogen Bonded

The ultraviolet photoelectron spectra of 2,7-diazatetracyclo[3.3.3.0.4,90.8,11]undecane (1) and its N,N-dimethyl- and methylene-bridged analogues 2 and 3 are documented. The spectrum of 2, which exhibits a nitrogen lone-pair splitting of 0.95 ± 0.1 eV, is interpreted on the basis of an interaction of "inside" lone pairs of the 1,2-diamine. Apparently this is the first report of a study of such an interaction. The spectrum of 1 is consistent with our view that 1 is an intramolecularly hydrogen bonded species in which the lone pairs are "inside–outside".

NUCLEAR MAGNETIC RESONANCE STUDIES: PART II. SOLVENT EFFECTS IN THE N.M.R. SPECTRA OF AROMATIC ALDEHYDES

1962 ◽  
Vol 40 (12) ◽  
pp. 2329-2338 ◽  
Author(s):  
R. E. Klinck ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Electron Distribution ◽  
Chemical Shifts ◽  
Aromatic Aldehydes ◽  
Solvent Interaction ◽  
Solvent Interactions ◽  
Magnetic Resonance Studies ◽  
Substituent Group ◽  
Solvent Shift ◽  
Solute Solvent Interaction

The chemical shifts for the aromatic and formyl protons of a series of substituted benzaldehydes have been obtained in a number of solvents. Relative to the shifts observed in chloroform, pronounced effects are observed in acetone and benzene solutions. In general, the shielding of these nuclei is decreased in acetone and increased in benzene, while in benzene the magnitude of the solvent shift for a given proton depends markedly on the nature of the substituent group. These results can be rationalized in terms of a specific solute-solvent interaction in which the site of association is governed by the electron distribution in the solute molecule. The nature of the solvent interactions in this and related systems is discussed.

scholarly journals Tautomerism in 1-hydroxy-2-naphthaldehyde Schiff bases: Calculation of tautomeric isomers using carbon-13 NMR

2003 ◽  
Vol 17 (4) ◽  
pp. 747-752 ◽  
Author(s):  
Salman R. Salman ◽  
Fadhil S. Kamounah
Keyword(s):  
Schiff Bases ◽  
Spectroscopic Data ◽  
Model Compound ◽  
Chemical Shifts ◽  
The Novel ◽  
Keto Form ◽  
Nmr Chemical Shifts ◽  
Tautomeric Equilibria ◽  
C Nmr ◽  
Hydrogen Bonded

Tautomeric equilibria in intramolecularly hydrogen bonded Schiff bases is studied on the basis of solution13C NMR chemical shifts. NMR spectroscopic data and comparison with two anils model compound, namely, salicylideneaniline (1A) and naphthalylidinequinoline (2A) were used to represent the enol (A) and the keto (H) forms. The13C NMR chemical shifts data of the novel series 4A (compounds, 4-12) were used together with the values13C chemical shifts data of compounds 1A and 2A to calculate the % keto form. The calculated % keto form of 3A was compared to that calculated for series 4A compounds.

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