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 N.M.R. chemical shifts and rotational barriers of para-substituted N,N-dimethylbenzamides

1978 ◽  
Vol 31 (12) ◽  
pp. 2615 ◽  
Author(s):  
CW Fong ◽  
SF Lincoln ◽  
EH Williams
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Rotational Barrier ◽  
Rotational Barriers

The carbon-13 N.M.R. chemical shifts for a series of para-substituted N,N-dimethylbenzamides have been measured. The substituent induced 13C shifts have been examined by a dual substituent parameter (DSP) method using Hammett-type constants. The barriers to rotation have also been correlated with Hammett-type constants by the DSP method and related to 13C substituent induced shifts. Substituent effects of the bromomethyl, dibromomethyl and tribromomethyl groups have been examined by using the chemical shift and rotational barrier probes.

Die Weiterleitung von substituenten- induzierten 13C-NMR-chemischen. Verschiebungen in para-substituierten 3-Phenylpropansäure-methylestern / The Transmission of Substituent-Induced 13C NMR Chemical Shifts in para-Substituted 3-Phenyl Propanoic Acid Methyl Esters

1980 ◽  
Vol 35 (7) ◽  
pp. 934-936 ◽  
Author(s):  
R. Radeglia ◽  
S. L. Spassov ◽  
R. Stefanova ◽  
S. D. Sofia
Keyword(s):  
13C Nmr ◽  
Chemical Shifts ◽  
Methyl Esters ◽  
Substituent Effects ◽  
Side Chain ◽  
Parameter Method ◽  
Propanoic Acid ◽  
Nmr Chemical Shifts ◽  
13C Nmr Chemical Shifts ◽  
Acid Methyl

Carbon-13 chemical shifts have been measured of para-substituted 3-phenyl propanoic acid methyl esters. The substituent-induced 13C shifts of the side chain were related to Hammett substituent effects by the dual substituent parameter method. The transmission of substituent effects and the factors that influence 13C shifts are discussed

Substituent effects on the N.M.R. spectra of carboxylic acid derivatives. II. 3H N.M.R. spectra of substituted benzamides and N-alkylbenzamides

1981 ◽  
Vol 34 (11) ◽  
pp. 2297 ◽  
Author(s):  
CJ O'Conner ◽  
RW Martin ◽  
DJ Calvert
Keyword(s):  
Carboxylic Acid ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Substituted Benzamides ◽  
Nitrogen Bond

The tritium n.m.r. spectra of 12 substituted benzamides and five series of N-alkylbenzamides have been measured, after tritiation of the amides, and the chemical shifts, δN3H, have been compared with δNH. The values correlate well when σR(BA) is substituted in the Taft DSP equation. Good correlations are also obtained with the Hammett σ parameter. The non-equivalence of the two amido protons of benzamides, arising from the barrier to rotation round the carbon-nitrogen bond, has been confirmed by use of triton n.m.r. spectroscopy.

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.

Substituent effects on the carbon-13 N.M.R. chemical shifts of side-chain carbons in aromatic systems

1977 ◽  
Vol 30 (2) ◽  
pp. 351 ◽  
Author(s):  
J Bromilow ◽  
RTC Brownlee ◽  
DJ Craik
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Side Chain ◽  
Parameter Method ◽  
Side Chains ◽  
Resonance Effects ◽  
Aromatic Systems

Carbon-13 chemical shifts have been measured for the side-chain carbon atoms of a number of meta- and para-disubstituted benzenes. The side chains examined were CN, CF3, Ac, CO2Et, Me, OMe and NMe2. The substituent-induced 13C shifts of these side chains were related to Hammett substituent effects by the Dual Substituent Parameter method and showed a widely varying dependence upon the blend of inductive and resonance effects. The transmission of substituent effects through aromatic systems and the factors that influence 13C shifts are discussed.

Solvent Effects on the Carbon – 13 NMR Chemical Shifts and Rotational Barriers of N,N-Dimethylbenzamide - Solvent Enhanced π Polarization

1981 ◽  
Vol 36 (5) ◽  
pp. 585-595 ◽  
Author(s):  
Clifford W. Fong ◽  
Hamish G. Grant
Keyword(s):  
Carbonyl Group ◽  
Chemical Shifts ◽  
Electron System ◽  
High Dilution ◽  
Hydrogen Bond Donor ◽  
Polar Solvents ◽  
Nmr Chemical Shifts ◽  
Rotational Barriers ◽  
Group Carbon ◽  
C Nmr

The 13C NMR chemical shifts of N,N-dimethylbenzamide in thirty solvents have been measured at high dilution. The solvent induced chemical shifts (s.i.c.s.) of the carbonyl group carbon atom in twenty three solvents and the thermodynamic barriers to rotation about the C-N bond in eleven solvents are linearly related to the solvent parameter, ET(30). Multi-parametric analysis of the carbonyl s.i.c.s. indicates hydrogen bond donor effects are more important than polar effects. Rotational barriers for N,N-dimethylbenzamide may be determined by measurement of the 13C chemical shift of the carbonyl group in a particular solvent. The s.i.c.s. of the aromatic ring carbon atoms may be explained by the polarization of the aromatic π electron system induced by the solvent enhanced polarization of the dimethylcarboxamido moiety. Hydrogen bonding solvents and polar solvents result in two effective dipoles on the dimethylcarboxamido moiety, which polarize the aromatic π electron system differently

Effects of Substituents on the Barriers to Rotation in Phenyl and Benzyl Carbamates

1986 ◽  
Vol 39 (3) ◽  
pp. 457 ◽  
Author(s):  
C Yamagami ◽  
N Takao ◽  
Y Takeuchi
Keyword(s):  
Free Energy ◽  
Steric Effect ◽  
Inductive Effect ◽  
Resonance Effect ◽  
Substituent Effects ◽  
Energy Of Activation ◽  
Resonance Effects ◽  
Free Energy Of Activation

The free energy of activation for rotation about the C-N bond (ΔG‡Tc) in substituted phenyl and benzyl N,N- dimethylcarbamates was determined by the 13C dynamic n.m.r. method. The ΔG‡Tc value depended linearly on Hammett's σ with positive p. We have separated the substituent effects into inductive and resonance effects by using dual substituent parameter ( d.s.p .) analysis, and found that the resonance effect is more important than the inductive effect for para derivatives, and vice versa for meta derivatives. General trends of electronic substituent effects on barriers to rotation in carbamates and structurally related amides are also discussed. The ortho steric effect was small.

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.

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