scholarly journals A Reconsideration of the Validity of Correlating Substituent-induced Proton Chemical Shifts in Aromatic Derivatives with Reactivity Parameters

1974 ◽  
Vol 52 (1) ◽  
pp. 39-45 ◽  
Author(s):  
Daniel A. Dawson ◽  
Gordon K. Hamer ◽  
William F. Reynolds
Keyword(s):  
Infinite Dilution ◽  
Chemical Shifts ◽  
Electronic Effects ◽  
Mo Calculations ◽  
Polar Medium ◽  
Charge Densities ◽  
Substituted Toluenes ◽  
Derivatives Of ◽  
Proton Chemical Shifts

Comparisons of 1H chemical shifts and charge densities (determined by CNDO/2 MO calculations) for 4-substituted derivatives of styrene, toluene, benzylchloride, and N,N,N-trimethylphenylammonium ion indicate that the chemical shifts primarily reflect intramolecular electronic effects. These effects are reflected by correlations of 1H chemical shifts with the F and R reactivity parameters of Swain and Lupton. It is concluded that it is valid to correlate substituent-induced chemical shifts for aromatic derivatives with divided reactivity parameters provided that (1) chemical shifts are measured at infinite dilution in a non-polar medium and (2) at least ten derivatives of each family are investigated.Calculations for 4-substituted toluenes indicate that there will be a small conformational dependence for substituent-induced benzylic proton chemical shifts.

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.

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.

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.

Proton Chemical Shifts, Long-Range Spin Coupling, and pi-Electron Distributions in Methoxy Derivatives of Salicylaldehyde and o-Hydroxyacetophenone.

1964 ◽  
Vol 18 ◽  
pp. 2313-2328 ◽  
Author(s):  
Sture Forsén ◽  
Björn Åkermark ◽  
Torbjörn Alm ◽  
D. R. Sparrow
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Spin Coupling ◽  
Electron Distributions ◽  
Derivatives Of ◽  
Proton Chemical Shifts

Proton chemical shifts and charge densities

2010 ◽  
Vol 94 (6) ◽  
pp. 124-124 ◽  
Author(s):  
H. Kloosterziel ◽  
M.A. Werner
Keyword(s):  
Chemical Shifts ◽  
Charge Densities ◽  
Proton Chemical Shifts

scholarly journals Investigations of Substituent Effects by Nuclear Magnetic Resonance Spectroscopy and All-valence Electron Molecular Orbital Calculations. II. 4-Substituted α-Methylstyrenes and α-t-Butylstyrenes

1973 ◽  
Vol 51 (6) ◽  
pp. 915-926 ◽  
Author(s):  
Gordon K. Hamer ◽  
Ian R. Peat ◽  
W. F. Reynolds
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electron System ◽  
Resonance Spectroscopy ◽  
Molecular Orbital Calculations ◽  
Electronic Effects ◽  
Partial Explanation ◽  
Charge Densities ◽  
Related Compounds ◽  
Molecular Framework

Substituent-induced 1H chemical shifts (S.C.S.) for 19 4-substituted α-methyl- and α-t-butylstyrenes have been determined at infinite dilution in C6H12 and 13C S.C.S. have been determined for 0.4 M solutions in CCl4. S.C.S. are correlated with field and resonance substituent parameters and compared with charge densities determined by CNDO/2 MO calculations. The variation of S.C.S. with the dihedral angle, ρ, between phenyl and vinyl groups and the overall pattern of S.C.S. can be largely accounted for by a model of substituent effects based on field, resonance, and π polarization effects, with conjugative interactions varying as cos2ρ. Both 13C chemical shifts and charge densities indicate that the π polarization effect consists of two components: (1) a through-space polarization of the vinyl system by the polar C—X bond and (2) polarization of the entire conjugated styrene π electron system. However, significant deviations are noted for some of the 1H S.C.S. correlations. The CNDO/2 calculations indicate that these deviations are primarily due to electronic effects not predicted by the model outlined above. CNDO/2 calculations for related compounds provide a partial explanation by indicating that the magnitude of the field effect depends upon the nature of the molecular framework.

ChemInform Abstract: PROTON CHEMICAL SHIFTS AND CHARGE DENSITIES

1975 ◽  
Vol 6 (40) ◽  
pp. no-no
Author(s):  
H. KLOOSTERZIEL ◽  
M. A. WERNER
Keyword(s):  
Chemical Shifts ◽  
Charge Densities ◽  
Proton Chemical Shifts

Investigations of Substituent Effects by Nuclear Magnetic Resonance Spectroscopy and All-valence Electron Molecular Orbital Calculations. I, 4-Substituted Styrenes

1973 ◽  
Vol 51 (6) ◽  
pp. 897-914 ◽  
Author(s):  
Gordon K. Hamer ◽  
Ian R. Peat ◽  
William F. Reynolds
Keyword(s):  
Field Effect ◽  
Chemical Shifts ◽  
Hydrogen Charge ◽  
Substituent Effects ◽  
Conclusive Evidence ◽  
Resonance Spectroscopy ◽  
Molecular Orbital Calculations ◽  
Electronic Effects ◽  
Charge Densities ◽  
Self Consistent

1H and 13C chemical shifts have been determined for over 20 4-substituted styrenes under conditions corresponding to infinite dilution in a non-polar medium. Correlations of the internal chemical shift difference for the β vinyl protons, Δδ(B − C) with electric field components estimated by a classical electrostatic calculation, with the field parameter F, and with hydrogen charge densities estimated by CNDO/2 MO calculations provide conclusive evidence for the existence of a through-space field effect. CNDO/2 calculations for 4-substituted 1-vinylbicyclo[2.2.2]octanes and ethylene–methylX pairs indicate that this through-space field effect has a geometric dependence similar to that predicted by the Buckingham equation.Correlations of vinyl 1H and 13C chemical shifts and charge densities with field, F, and resonance, R, parameters provide a self-consistent picture of electronic effects in these compounds. 1H chemical shifts for some derivatives are affected by magnetic effects but this does not obscure the overall pattern of electronic effects. This pattern of electronic effects can be completely accounted for by a model which assumes that substituent effects can be transmitted through space (field effects), via conjugative interactions (resonance effects) or by polarization of the styrene π electron system by the polar C—X bond (π polarization effects). The latter effect appears to be more important than previously realized.1H correlations with F and R are used to estimate self-consistent and apparently reasonable Δχ values for C≡N and C≡C—H groups and F and R values for carbonyl substituents and (CH3)3M substituents (M = Si, Ge, Sn, and Pb). The halogens give anomalous results. A comparison of various correlations suggests that these anomalies are magnetic in origin.

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