Carbon-13 chemical shifts as a probe for conformational and electronic effects in alkyl vinyl ethers

1983 ◽  
Vol 61 (3) ◽  
pp. 488-493 ◽  
Author(s):  
John G. K. Webb ◽  
David K. Yung
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Electronic Effects ◽  
Vinyl Ethers ◽  
Resonance Effects ◽  
Polarization Mechanism ◽  
Chemical Shift Data ◽  
Vinyl Group ◽  
The Relationship ◽  
Geminal Substituent

The principle of additivity of substituent chemical shifts (SCS) is applied to the carbon-13 chemical shifts of β carbons (δβ) in a number of 1,1-disubstituted ethylenes and propenes, which includes some α-substituted alkyl vinyl ethers. An additivity relationship is observed for 34 compounds that indicates an independent polarization mechanism across the double bond for each geminal substituent. Positive deviations from additivity are observed for compounds bearing bulky substituents. The magnitude of deviations is taken as an indication of the severity of steric interactions among substituents.Reductions in efficiency of transmission of substituent effects in ring substituted α-phenyl alkyl vinyl ethers, relative to para-substituted styrenes, are interpreted as the result of a variable dihedral angle between the ring and vinyl group. An explanation of the relationship between conformation and transmission of substituent effects is presented as an alternative to existing views. An angular dependence of π-polarization and resonance effects is consistent with the chemical shift data.

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.

scholarly journals Effect of substituents on the 13C-NMR chemical shifts of 3-methylene-4-substituted-1, 4-pentadienes - Part I

2003 ◽  
Vol 68 (2) ◽  
pp. 67-76 ◽  
Author(s):  
Natasa Valentic ◽  
Zeljko Vitnik ◽  
Sergei Kozhushkov ◽  
Majere de ◽  
Gordana Uscumlic ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Heat Of Formation ◽  
Electronic Effects ◽  
Resonance Effects ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Consistent Picture ◽  
The One ◽  
Semi Empirical

The principles of linear free energy relationships were applied to the 13C substituent chemical shifts (SCS) of the carbon atoms in the unsaturated chain of 3-methylene-4-substituted-1,4-pentadienes. Correlations of the SCS with the substituent parameters of Swain and Lupton provide a mutually consistent picture of the electronic effects in these compounds. The pattern of the electronic effects can be fully rationalized by a model based on the direct transmission of substituent effects through-space (direct through-space field effects), and via conjugative interactions (resonance effects), or by substituent-induced polarization of the ?-system in the unsaturated chain (?-polarization effect). Semi-empirical MNDO-PM3 calculations suggest the s-cis conformation of 3-methylene-4-substituted-1,4-pentadienes as the one with minimal heat of formation.

scholarly journals Substituenteneinflüsse auf die 13C–NMR-chemischen Verschiebungen cis- und trans-konfigurierter Trimethincyanine / Substituent Effects on the 13C NMR Chemical Shifts of Trimethincyanines with cis and trans Configuration

1976 ◽  
Vol 31 (12) ◽  
pp. 1641-1645 ◽  
Author(s):  
Walter Grahn
Keyword(s):  
13C Nmr ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Electron Systems ◽  
Coupling Constant ◽  
Electronic Effects ◽  
Nmr Chemical Shifts ◽  
Monosubstituted Benzenes ◽  
Cis And Trans ◽  
C Nmr

The 13C NMR chemical shifts of fifteen 6 substituted 2,3-dihydro-1,4-diazepinium salts (cis trimethincyanines) (1) and twelve 2 substituted bis(dimethylamino)trimethinium salts (trans trimethincyanines) (2) have been determined. A comparison of the substituentinduced shifts (13C SCS) of 1 and 2 allows no distinction between steric and electronic effects. In the three 6 п-electron systems 1, 2 and monosubstituted benzenes the 13C SCS are similar for the substituent bearing carbon atoms. A surprisingly large 4JFCCNC coupling constant has been observed.

Coplanarity in 2,6-Dimethylazobenzenes: a 13C N.M.R. Study

1993 ◽  
Vol 46 (6) ◽  
pp. 887 ◽  
Author(s):  
CJ Byrne ◽  
DAR Happer
Keyword(s):  
Chemical Shifts ◽  
Substantial Effect ◽  
The Other ◽  
Methyl Groups ◽  
Electronic Effects ◽  
Resonance Effects

A number of 3- and 4-X-2′,6′-dimethylazobenzenes and 4-X-2,6-dimethylazobenzenes have been prepared, and their 13C N.M.R . Spectra have been measured. Comparison of the effect of X on the 13C N.M.R . chemical shifts for C4′ with that for the corresponding azobenzenes has been used as a probe for exploring the influence of the two introduced ortho-methyl groups on the degree of coplanarity of the azobenzene system and the efficiency of transmission of electronic effects from one ring to the other. The results support previous studies that have suggested that the methyl groups have a substantial effect on the planarity of the system, but, surprisingly, suggest that such loss of planarity has relatively little effect on the efficiencies of transmission of both polar and resonance effects between the two rings.

13C NMR and IR study of substitution effects and mass spectra of biphenyl analogues of α-cyanochalcones

1984 ◽  
Vol 49 (2) ◽  
pp. 421-432
Author(s):  
Štefan Marchalín ◽  
Petr Trška ◽  
Josef Kuthan
Keyword(s):  
13C Nmr ◽  
Mass Spectra ◽  
Chemical Shifts ◽  
Substitution Effects ◽  
Electronic Effects ◽  
Consistent Picture ◽  
Ir Study ◽  
The Relationship ◽  
Hammett Parameters ◽  
C Nmr

Thirteen biphenyl analogues of α-cyanochalcones IIa-IIm were prepared by condensation of p-phenylbenzoylacetonitrile (I) with p-substituted benzaldehydes. Their 13C NMR chemical shifts were measured and correlated with the Hammett parameters (σ, σ+) and the Swain-Lupton reactivity parameters. A consistent picture of the transmission of the substituent (electronic) effects through the carbon skeleton of the studied compounds was obtained. The relationship between the structure of synthetized α-cyanochalcones and their mass spectra is discussed.

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