Pi‐Electron Charge Densities and Chemical Shifts in Nitrogen Heterocyclics

1969 ◽  
Vol 50 (10) ◽  
pp. 4262-4282 ◽  
Author(s):  
T. B. Cobb ◽  
J. D. Memory
Keyword(s):  
Chemical Shifts ◽  
Electron Charge ◽  
Charge Densities

Photochromic systems. Part 1. Structural and spectroscopic study of photochromically active products of Stobbe condensation. 2,3-Dibenzylidenesuccinic acid and its anhydride

1990 ◽  
Vol 68 (5) ◽  
pp. 741-746 ◽  
Author(s):  
P. Adriaan Davidse ◽  
Jan L. M. Dillen ◽  
Anton M. Heyns ◽  
Tomasz A. Modro ◽  
Petrus H. van Rooyen
Keyword(s):  
Cinnamic Acid ◽  
Structural Changes ◽  
Chemical Shifts ◽  
Spectroscopic Properties ◽  
Shielding Effect ◽  
Electron Charge ◽  
Hydrogen Atoms ◽  
Steric Strain ◽  
Space Group ◽  
Charge Densities

E,E-2,3-Dibenzylidenesuccinic acid (2) and its anhydride (1) were synthesized, their crystal structures and 1H and 13C nuclear magnetic resonance spectra were determined, and electron charge densities of carbon atoms were calculated. These results were related to the corresponding data available for E-cinnamic acid (3) in order to evaluate the effect of structural changes in a series 3 → 2 → 1 on the molecular parameters and spectroscopic properties of the cinnamic system. In the molecule of 2 most of the steric strain is released by the rotation about the C(α)—C(α′) bond giving rise to a structure consisting of two, approximately independent, cinnamic acid moieties. In 1, severe steric strain is introduced, as demonstrated by the unusually large values of the CCC bond angles exocyclic with respect to the anhydride ring, as well as by significant deviations from the plane of the cinnamic skeleton. The geometry of 1 results in an intramolecular shielding of the aromatic hydrogen atoms due to the proximity of the two benzene rings; this shielding effect for the ortho, meta, and para hydrogen atoms correlates well with the intramolecular distances between the corresponding positions of both rings. The common linear relationship between 13C chemical shifts and the electron charge densities on the given carbon atom has been obtained for compounds 1, 2, and 3.Crystal data. Anhydride (1): space group P21/c with a = 13.536(3), b = 14.391(3), c = 7.159(1) Å; β = 98.69(1)°; Rw = 0.029 and R = 0.055. Succinic acid (2): space group [Formula: see text] with a = 8.881(3), b = 9.786(1), c = 11.355(3) Å; α = 85.56(1), β = 88.76(2), γ = 69.46(2)°; Rw = 0.048 and R = 0.081. This compound cocrystallizes with one molecule of the solvent (acetic acid). Keywords: photochromic, cinnamic, succinic.

CNDO/2-Elektronenladungsdichten und 13C-chemische Verschiebungen von Phenylacetylenen / CNDO/2-Electron Charge Densities and 13C-Chemical Shifts of Phenylacetylenes

1972 ◽  
Vol 27 (12) ◽  
pp. 1772-1776 ◽  
Author(s):  
L Klasinc ◽  
J.V. Knop ◽  
H.-J Meiners ◽  
W Zeil
Keyword(s):  
Charge Transfer ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Electron System ◽  
Total Charge ◽  
Electron Charge ◽  
Substituted Benzenes ◽  
Charge Densities ◽  
Inductive Effects ◽  
Monosubstituted Benzenes

AbstractThe 13C FT NMR spectra of phenylacetylene (1), p-methoxyphenylacetylene (2), p-fluorophenyl-acetylene (3), p-chlorophenylacetylene (4), p-bromophenylacetylene (5), p-ethylphenylacetylene (6) and p-isopropylphenylacetylene (7) as well as of a number of monosubstituted benzenes have been measured. The 13 C-chemical shifts in these compounds are correlated with the total charge densities at the corresponding carbon atoms, calculated by the CNDO/2 method. The present results show that a simple additivity exists between 13C-chemical shifts in substituted benzenes, phenylacetylene and substituted phenylacetylenes and that practically no charge transfer between the linked sub-stituted phenyl and the ethinyl groups takes place. The interaction of the ethinyl substituent and the π-electron system can mainly be attributed to inductive effects.

Nuclear Magnetic Resonance Chemical Shifts of some Monosubstituted Isothiazoles

1975 ◽  
Vol 53 (4) ◽  
pp. 596-603 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Thomas R. Clem ◽  
Edwin D. Becker
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Charge Densities ◽  
Monosubstituted Benzenes ◽  
Proton Chemical Shifts ◽  
Nuclear Magnetic

Carbon-13 and proton chemical shifts have been measured for several monosubstituted isothiazoles. Substituent effects upon these chemical shifts are compared with those observed for monosubstituted benzenes, pyridines, and thiophenes. In general the observed substituent effects in the isothiazoles and thiophenes closely parallel one another. Correlations between the observed carbon-13 Chemical shifts and CNDO/2 calculated charge densities are examined.

Erratum: Electron charge densities at conduction-band edges of semiconductors

1987 ◽  
Vol 35 (17) ◽  
pp. 9308-9309
Author(s):  
Steven L. Richardson ◽  
Marvin L. Cohen ◽  
Steven G. Louie ◽  
James R. Chelikowsky
Keyword(s):  
Conduction Band ◽  
Electron Charge ◽  
Charge Densities

CMR CHEMICAL SHIFTS AND TOTAL CHARGE DENSITIES OF [2.2]CYCLOPHANES. THE EFFECT OF TRANSANNULAR Π- Π INTERACTION

1977 ◽  
Vol 6 (8) ◽  
pp. 865-868 ◽  
Author(s):  
Tetsuo Takemura ◽  
Kazushi Tokita ◽  
Shoichi Kondo ◽  
Nobuo Mori
Keyword(s):  
Chemical Shifts ◽  
Total Charge ◽  
Charge Densities

scholarly journals Effects of substituents on the 1H-NMR chemical shifts of 3-methylene-2-substituted-1, 4-pentadienes

2003 ◽  
Vol 68 (7) ◽  
pp. 525-534 ◽  
Author(s):  
Natasa Valentic ◽  
Gordana Uscumlic
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electronic Effects ◽  
Resonance Effects ◽  
Charge Densities ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Consistent Picture ◽  
Vinyl Group ◽  
Proton Chemical Shifts

The principle of linear free energy relationships was applied to the 1H chemical shifts of the ?-vinyl proton atoms of 3-methylene-2-substituted-1,4-pentadienes. The correlations of the proton chemical shifts with Swain and Lupton substituent parameters provide a mutually consistent picture of the electronic effects in these compounds. The overall pattern of proton chemical shifts can be largely accounted for by a model of substituent effects based on field, resonance and ? polarization effects. Owing to the particular geometric arrangement of the vinyl group in 3-methylene-2-substituted-1,4-pentadienes, the ?-vinyl protons HB and HC have different sensitivities to polar and resonance effects. The different sensitivities of the 1H chemical shifts to resonance effects reveals some effects not predicted by the model outlined above. Evidence is presented that demonstrates that both the 1H and 13C chemical shifts for these compounds reflect their ground-state charge densities.

Some ab Initio Calculations on Indole, Isoindole, Benzofuran, and Isobenzofuran

1974 ◽  
Vol 29 (4) ◽  
pp. 624-632 ◽  
Author(s):  
J. Koller ◽  
A. Ažman ◽  
N. Trinajstić
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Chemical Shifts ◽  
Dipole Moments ◽  
Molecular Properties ◽  
Ionization Potentials ◽  
Charge Densities ◽  
Homo Lumo

Ab initio calculations in the framework of the methodology of Pople et al. have been performed on indole, isoindole, benzofuran. and isobenzofuran. Several molecular properties (dipole moments, n. m. r. chemical shifts, stabilities, and reactivities) correlate well with calculated indices (charge densities, HOMO-LUMO separation). The calculations failed to give magnitudes of first ionization potentials, although the correct trends are reproduced, i. e. giving higher values to more stable isomers. Some of the obtained results (charge densities, dipole moments) parallel CNDO/2 values.

Revisions of Structural Assignments for l-Methyl-(3 and 5)-amino-4-nitropyrazoles and Related Compounds

1971 ◽  
Vol 49 (21) ◽  
pp. 3566-3569 ◽  
Author(s):  
Misbahul Ain Khan ◽  
Brian M. Lynch
Keyword(s):  
Chemical Shifts ◽  
Charge Densities ◽  
Related Compounds ◽  
Proton Chemical Shifts

Amino proton chemical shifts recorded for the compounds described as 5-amino-1-methyl-4-nitropyrazole and the 3-amino isomer (3) are inconsistent with charge densities calculated from simple H.m.o. treatments.Unequivocal synthesis of 5-amino-1-methyl-4-nitropyrazole from 5-amino-1-methylpyrazole proves that the assignments should be interchanged; the structures of compounds derived from these amino-nitropyrazoles are revised accordingly.

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