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.

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 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.

Substituent effects on the chemical shifts of the bridge protons of benzonorbornenes

1967 ◽  
Vol 45 (11) ◽  
pp. 1185-1193 ◽  
Author(s):  
Naoki Inamoto ◽  
Shozo Masuda ◽  
Kazuo Tori ◽  
Katsutoshi Aono ◽  
Hiroshi Tanida
Keyword(s):  
Benzene Ring ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Electron System ◽  
Electronic Interaction ◽  
Orbital System ◽  
Significant Difference ◽  
Bridge Carbon ◽  
Hammett Relationship ◽  
Good Agreement

The substituent effects on the chemical shifts of the C9 bridge protons in a series of 6-substituted benzonorbornenes and benzonorbornadienes, and on those of the C2 protons in 5-substituted 2-indanols, were investigated. They were linearly correlated with the modified Hammett relationship τR − τH = ρ (σm + σp)/2. The ρ values obtained from the anti-C9 protons in the bornenes and bornadienes were slightly but significantly larger than those from the corresponding syn protons, whereas no significant difference was observed between the ρ values obtained from syn-9-benzonorbornenols and the indanols. The larger ρanti values were explained in terms of a stereospecific electronic interaction between the π-electron system of the benzene ring and the orbital system of the bridge carbon. In addition, it was shown that the above modified Hammett relationship gives generally a good agreement with the substituent effects on the aliphatic constituents of benzocyclenes and analogous compounds.

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]

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.

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.

Carbon-13 N.M.R. chemical shifts and rotational barriers of ortho-substituted N,N-dimethylbenzamides

1978 ◽  
Vol 31 (12) ◽  
pp. 2623 ◽  
Author(s):  
CW Fong ◽  
SF Lincoln ◽  
EH Williams
Keyword(s):  
Carbonyl Group ◽  
Steric Effect ◽  
Chemical Shifts ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Parameter Method ◽  
Methyl Groups ◽  
Rotational Barriers ◽  
Effect Parameter ◽  
Nitrogen Bond

The barriers to rotation about the carbon-nitrogen bond and the carbon- 13 N.M.R. chemical shifts of a series of 2-substituted N,N- dimethylbenzamides have been measured. The substituent effects have been examined by a multi-substituent parameter method incorporating a steric effect parameter. The barriers to rotation are subject to a large steric effect, whilst the carbon-13 chemical shifts of the carbonyl group and the methyl groups are dominated by the resonance effect.

Carbon-13 magnetic resonance: hydrogen involvement in γ-anti substituent effects

1981 ◽  
Vol 59 (19) ◽  
pp. 2870-2875 ◽  
Author(s):  
T. P. Forrest ◽  
J. Thiel
Keyword(s):  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Methyl Groups

Chemical shifts have been determined for the carbons in a series of 3,3-dimethylcyclohexyl derivatives, (substituent = H, CH3, NH2, OH, Cl, Br, I). Comparison of the γ-anti substituent effects at carbons 3 and 5 indicates that presence of axial protons on these carbons causes increased shielding by all of the above substituents. The shielding by γ-anti substituents is decreased by the replacement of either the α or γ protons by methyl groups; the extent of the decrease is dependent upon the substituent and upon the position of the hydrogen which is replaced.

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.

Sign in / Sign up

Export Citation Format

Share Document