Substituent effects on aromatic proton chemical shifts. VII. Further examples drawn from disubstituted benzenes

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.

Download Full-text

Correlations of substituent effects on proton and fluorine chemical shifts with inverse ionization potentials

Canadian Journal of Chemistry ◽

10.1139/v67-506 ◽

1967 ◽

Vol 45 (24) ◽

pp. 3143-3151 ◽

Cited By ~ 15

Author(s):

T. Schaefer ◽

F. Hruska ◽

H. M. Hutton

Keyword(s):

Electric Fields ◽

Chemical Shifts ◽

Substituent Effects ◽

Group Iv ◽

The Other ◽

Ionization Potentials ◽

Time Dependent ◽

Practical Application ◽

Methyl Proton ◽

Proton Chemical Shifts

The fluorine and proton chemical shifts in some geminally disubstituted vinylidene fluorides and ethylenes are discussed. For these compounds, at least, there are difficulties with an interpretation based on intramolecular time-dependent electric fields. On the other hand, the shifts correlate with the inverse ionization potentials of the substituents, indicating a paramagnetic effect arising from the second term in Ramsey's expression. It is suggested that the effect operates via the bonds and not across space. Methyl proton shifts in a series of substituted methyl compounds of group IV, V, and VI elements show similar correlations. A practical application of the correlation to spectral analysis problems is given.

Download Full-text

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

Journal of the Serbian Chemical Society ◽

10.2298/jsc0307525v ◽

2003 ◽

Vol 68 (7) ◽

pp. 525-534 ◽

Cited By ~ 1

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.

Download Full-text