Linear relationships between carbon-13 and proton chemical shifts and Hückel π-electron densities in diazoles and triazoles

1968 ◽  
Vol 0 (21) ◽  
pp. 1337-1337 ◽  
Author(s):  
Brian M. Lynch
Keyword(s):  
Chemical Shifts ◽  
Electron Densities ◽  
Linear Relationships ◽  
Proton Chemical Shifts

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.

Proton chemical shifts and electron densities

1962 ◽  
Vol 34 ◽  
pp. 18 ◽  
Author(s):  
B. P. Dailey ◽  
Albert Gawer ◽  
W. C. Neikam
Keyword(s):  
Chemical Shifts ◽  
Electron Densities ◽  
Proton Chemical Shifts

Proton chemical shifts and ?-electron densities

1968 ◽  
Vol 9 (4) ◽  
pp. 540-544
Author(s):  
R. M. Aminova ◽  
I. D. Morozova
Keyword(s):  
Chemical Shifts ◽  
Electron Densities ◽  
Proton Chemical Shifts

CNDO/2 Electron Densities and Proton Chemical Shifts

1971 ◽  
Vol 49 (10) ◽  
pp. 1779-1781 ◽  
Author(s):  
John F. Sebastian ◽  
John R. Grunwell
Keyword(s):  
Linear Dependence ◽  
Chemical Shifts ◽  
Electron Densities ◽  
Proton Chemical Shifts

An approximate linear dependence of the proton shifts on the CNDO/21 calculated electron densities on hydrogen for C5H5−, C6H6, C7H7+, C5H5NH+, and C6H5CH2− has been found. The significance and limitations of the correlation are discussed.

Purine analogues. I. The status of Hückel molecular orbital calculations as predictors of proton shifts, basic strengths, and reactivity

1969 ◽  
Vol 47 (7) ◽  
pp. 1129-1138 ◽  
Author(s):  
Brian M. Lynch ◽  
Allan J. Robertson ◽  
John G. K. Webb
Keyword(s):  
Nucleophilic Substitution ◽  
Molecular Orbital ◽  
Chemical Shifts ◽  
Ionic Species ◽  
Membered Ring ◽  
Molecular Orbital Calculations ◽  
Electron Densities ◽  
Purine Analogues ◽  
The Status ◽  
Proton Chemical Shifts

A detailed series of molecular orbital calculations based on the HMO method has been made for the various possible ionic species of purine, pyrazolo(3,4-d)pyrimidine, v-triazolo(4,5-d)pyrimidine, and pyrazolo(3,4-b)pyridine. π-Electron densities and localization and delocalization energies for nucleophilic substitution have been derived.The results are compared with the observed proton chemical shifts in the conjugate acids of these molecules, with the relative rates of nucleophilic piperidinodehalogenations in the neutral molecules, and with the ionization constants.It is concluded that it is possible to reconcile the calculations with experimental results for the various positions within a six-membered ring, but that positions in six- and five-membered rings cannot be directly compared. The electron densities seem to be of little value in correlating the observed ionization patterns of purines and their analogues.

scholarly journals Methyl Substitution Effects on the Proton Chemical Shifts in Benzene

1966 ◽  
Vol 21 (5) ◽  
pp. 609-615 ◽  
Author(s):  
G. S. Reddy
Keyword(s):  
Dipole Moment ◽  
Inverse Relationship ◽  
Chemical Shifts ◽  
Substitution Effects ◽  
Electron Densities ◽  
Methyl Proton ◽  
Methyl Substitution ◽  
Calculated Dipole Moment ◽  
Proton Chemical Shifts ◽  
Good Agreement

Methyl substitution effects on aromatic and methyl proton chemical shifts in several mono-, di-, and trimethyl benzenes are studied. A new method for obtaining the changes in the ring proton chemical shifts from those of methyl proton shifts at the corresponding positions is used. The extra π-electron densities in toluene are calculated using the already known relation between the π-electron densities and the proton shifts in aromatic systems. An inverse relationship is obtained between the ionization potentials and the total methyl effects on the chemical shifts in this series of compounds as one would expect. Dipole moment of toluene is calculated, and a reasonably good agreement is found between the experimentally observed and the calculated dipole moment.

Proton chemical shifts and electron densities in aromatic and heteroaromatic molecules. II. Derivatives of pyrrole and furan

1967 ◽  
Vol 20 (7) ◽  
pp. 1325 ◽  
Author(s):  
PJ Black ◽  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Electron Distribution ◽  
Chemical Shifts ◽  
Membered Ring ◽  
Electron Densities ◽  
Heteroaromatic Compounds ◽  
Derivatives Of ◽  
Proton Chemical Shifts

In this paper, the methods outlined in Part I are used to estimate the electron distribution from the proton chemical shifts in a series of five-membered ring heteroaromatic compounds. The systems studied are pyrrole and furan, their benzo and dibenzo derivatives, indazole, indolizine, the azaindolizines, and purine. It is found that the estimated excess charges are not as closely represented by the BJ VESCF method as was the case for the azine derivatives and that the role of the σ-electrons is in urgent need of closer investigation.

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