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.

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.

Carbon-13 Substituent-Induced Chemical Shifts: Monosubstituted Benzene Derivatives

1992 ◽  
Vol 57 (3) ◽  
pp. 497-507 ◽  
Author(s):  
Otto Exner ◽  
Miloš Buděšínský
Keyword(s):  
Benzene Ring ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
The Other ◽  
Correlation Equations ◽  
Benzene Derivatives ◽  
Complex Mechanism ◽  
Monosubstituted Benzene ◽  
Resonance Effects ◽  
Other Hand

Carbon-13 NMR spectra of twelve monosubstituted benzene derivatives were measured in deuterochloroform. Together with the literature data a set of 35 systematically chosen substituents was obtained on which some thirty correlation equations were tested. As anticipated only substituent chemical shifts (SCS) in the position 4 are controlled by inductive and resonance effects, and can be correlated by dual substituent parameters (DSP). For the other positions DSP were not successful and more sophisticated equations are not much telling. On the other hand, the direct relations between two series of SCS are usually more precise and simple to understand. It is concluded that SCS in benzene ring need not be controlled by too complex mechanism but simply by different factors than by inductive and resonance effects.

Etude par résonance magnétique nucléaire de composés organiques contenant des chalcogènes. I. L'anisole et ses analogues soufré, sélénié et tellure

1978 ◽  
Vol 56 (15) ◽  
pp. 2008-2012 ◽  
Author(s):  
Gabriel Llabres ◽  
Marcel Baiwir ◽  
Léon Christiaens ◽  
José Denoel ◽  
Léopold Laitem ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Heavy Atom ◽  
Methyl Groups ◽  
Electronic Effects ◽  
Methyl Halides ◽  
Planar Configuration ◽  
Résonance Magnétique ◽  
Atom Effect

Results are reported of a study by 1H and 13C nuclear magnetic resonance of anisole, thioanisole, selenoanisole and telluroanisole as well as of several of their para-substituted derivatives. If these compounds are considered as substituted methyl groups, they display a behaviour analogous to that of the methyl halides. It is possible to demonstrate that a linear relation exists between the proton and the carbon chemical shifts in the anisole series as well as in the methyl halides. Although these results most frequently are interpreted in terms of electronic effects, a 'heavy atom effect' must be invoked for the tellurium compounds. The experimental results do not contradict the hypothesis that the compounds studied have a planar configuration [Journal translation]

The application of the Hammett equation to 13C N.M.R. spectrometry. VI. Remote ring effects in azobenzenes and stilbenes

1983 ◽  
Vol 36 (10) ◽  
pp. 2083 ◽  
Author(s):  
D Christoforou ◽  
DAR Happer
Keyword(s):  
Chemical Shifts ◽  
Phenyl Group ◽  
Resonance Interaction ◽  
Parameter Analysis ◽  
The Other ◽  
Hammett Equation ◽  
Resonance Effects ◽  
Inductive Effects

The 13C n.m.r. chemical shifts for the non-substituted rings of azobenzene, stilbene, 26 monosubstituted azobenzenes and 28 monosubstituted stilbenes are reported. The effects of substituents in one ring on the chemical shifts of the other have been interpreted in terms of their inductive and resonance effects by means of a dual substituent parameter analysis. The results show that inductive effects are transmitted to the remote ring from the meta and para positions with equal efficiencies and polarize the phenyl group independently of the rest of the molecule. Resonance interaction is greatest when the substituent is para to the azo or vinylene linking group and is relayed with greatest efficiency to the ortho and para carbons of the remote ring. The results of the study are compared with previously unreported data for the corresponding ring carbons of the ethyl arylazo- and arylethenyl-cinnamates, and with literature data on para-substituted biphenyls and terphenyls.

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.

Electronic effects of halogen-substituted methyl groups

1980 ◽  
Vol 33 (6) ◽  
pp. 1291 ◽  
Author(s):  
CW Fong
Keyword(s):  
Benzene Ring ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Methyl Groups ◽  
Electronic Effects ◽  
Substituted Toluenes ◽  
Molecular Deformations

The electronic effects of the halogen-substituted methyl groups, CHnX3-n, where X is F, Cl, Br or I, have been examined by 13C n.m.r, spectroscopy in a series of α-halogen-substituted toluenes. The substituent chemical shifts of all carbon atoms, as well as the σI and σR0 substituent parameters derived from a dual substituent parameter (DSP) analysis, are examined in terms of hyperconjugative and π-inductive substituent effects. Bulky CHnX3-n substituents cause molecular deformations of the benzene ring, consequently invalidating the derivation of substituent parameters from a DSP analysis.

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.

17O and 13C NMR spectra of some geminal diacetates

1988 ◽  
Vol 53 (3) ◽  
pp. 588-592 ◽  
Author(s):  
Antonín Lyčka ◽  
Josef Jirman ◽  
Jaroslav Holeček
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
The Other ◽  
13C Nmr Spectra ◽  
Other Hand ◽  
Carboxylic Esters ◽  
C Nmr ◽  
Oxygen Atoms

The 17O and 13C NMR spectra of eight geminal diacetates RCH(O(CO)CH3)2 derived from simple aldehydes have been measured. In contrast to the dicarboxylates R1R2E(O(CO)R3)2, where E = Si, Ge, or Sn, whose 17O NMR spectra only contain a single signal, and, on the other hand, in accordance with organic carboxylic esters, the 17O NMR spectra of the compound group studied always exhibit two well-resolved signals with the chemical shifts δ(17O) in the regions of 183-219 ppm and 369-381 ppm for the oxygen atoms in the groups C-O and C=O, respectively.

Electronic effects on13C NMR chemical shifts of substituted 1,3,4-thiadiazolium salts

2001 ◽  
Vol 39 (4) ◽  
pp. 182-186 ◽  
Author(s):  
Ana Cristina Souza dos Santos ◽  
Aurea Echevarria
Keyword(s):  
Chemical Shifts ◽  
Electronic Effects ◽  
Nmr Chemical Shifts

Proximity effects in 29Si, 13C, and 1H NMR spectra of ortho substituted phenoxytrimethylsilanes

1990 ◽  
Vol 55 (8) ◽  
pp. 2019-2026 ◽  
Author(s):  
Jan Schraml ◽  
Václav Chvalovský ◽  
Harald Jancke ◽  
Peter Koehler ◽  
Mikhail F. Larin ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
1H Nmr ◽  
Proximity Effect ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Proximity Effects ◽  
1H Nmr Spectra ◽  
Methyl Groups ◽  
Conformational Preferences

NMR Spectra of eight ortho substituted phenoxytrimethylsilanes, 2-X-C6H4-OSi(CH3)3 (X = Cl, Br, OCH3, NH2, NO2, OSi(CH3)3, CH3, and H), are reported. In contrast to analogous ortho substituted methoxybenzenes the 13C chemical shifts of C-2 and C-6 aromatic carbons do not exhibit consistent trends indicating different conformational preferences in the trimethylsiloxybenzenes. Under the influence of the ortho substituents the nuclei of OSi(CH3)3 group (29Si, 13C, and 1H) are deshielded; compounds with X = CH3 (and H) appear anomalous in this respect. It is argued that this proximity effect is not due to an interaction involving terminal methyl groups but involves the oxygen atom of the OSi(CH3)3 group; it is most likely due to an interaction with unshared electrons of the ortho substituent.

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