1H chemical shifts in NMR. Part 20— Anisotropic and steric effects in halogen substituent chemical shifts(SCS), a modelling andab initio investigation

2004 ◽  
Vol 42 (5) ◽  
pp. 436-444 ◽  
Author(s):  
Raymond J. Abraham ◽  
Mehdi Mobli ◽  
Richard J. Smith
Keyword(s):  
Chemical Shifts ◽  
Steric Effects

14N-NMR-Untersuchungen an Aminophosphinen / 14N NMR Studies on Aminophosphines

1978 ◽  
Vol 33 (5) ◽  
pp. 515-520 ◽  
Author(s):  
K. Barlos ◽  
H. Nöth ◽  
B. Wrackmeyer
Keyword(s):  
Chemical Shifts ◽  
Steric Effects ◽  
Nmr Studies ◽  
Π Interactions ◽  
Nuclear Shielding ◽  
14N Nmr

Abstract14N chemical shifts of a series of cyclic and noncyclic aminophosphines are reported. The nuclear shielding of nitrogen decreases with increasing number of halogen substituents at phosphorus as well as with increasing number of phosphinyl groups attached to nitrogen. In addition to the influence of electronegativity PN(π)-interactions may account for the observed shielding. Steric effects are discussed.

Steric effects on nitrogen-15 chemical shifts of 4-aminooxanes (tetrahydropyrans), 4-aminothianes, and the corresponding N,N-dimethyl derivatives. Use of nitrogen-15 shifts as an aid in stereochemical analysis of these heterocyclic systems

1982 ◽  
Vol 47 (10) ◽  
pp. 1933-1935 ◽  
Author(s):  
Pullachipatti K. Subramanian ◽  
Nallappan ChandraSekara ◽  
Kondareddiar Ramalingnam ◽  
Phanviet M. Tan ◽  
George C. Levy ◽  
...  
Keyword(s):  
Chemical Shifts ◽  
Steric Effects ◽  
Stereochemical Analysis

Quantum Chemical Systematization of the PMR Spectra of Some N-(Pyridyl)-pyrrole Derivatives

1975 ◽  
Vol 30 (9-10) ◽  
pp. 784-787 ◽  
Author(s):  
P. Dvortsák ◽  
G. Náray-Szabó ◽  
L. Vasvári-Debreczy
Keyword(s):  
Chemical Shift ◽  
Charge Distribution ◽  
Linear Relation ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Steric Effects ◽  
Pyrrole Derivatives ◽  
Pmr Spectra ◽  
Net Charges

In the case of a number of N-(pyridyl)-pyrrole derivatives a linear relation was found between the PMR chemical shifts of the olefinic and aromatic protons and the adjacent carbon net charges. The charge distribution was obtained as a sum of σ- and π-parts, calculated by the Del Re and PPP methods, respectively. Steric effects were treated on the basis of chemical shift anomalies.

Carbon-13 Magnetic Resonance: the Stereochemistry of 1,2- and 1,3-Dimethyl-4-phenylpiperidine Derivatives

1973 ◽  
Vol 51 (11) ◽  
pp. 1782-1789 ◽  
Author(s):  
Alan J. Jones ◽  
A. F. Casy ◽  
K. M. J. McErlane
Keyword(s):  
Magnetic Resonance ◽  
Conformational Change ◽  
Solvent Effects ◽  
Chemical Shifts ◽  
Phenyl Group ◽  
Steric Effects ◽  
Methyl Group ◽  
Charge Polarization ◽  
Magnetic Resonance Spectra

The carbon-13 magnetic resonance spectra of the diastereoisomers of 1,2-dimethyl- (1) and 1,3-dimethyl-4-phenylpiperidin-4-ol (2), their esters and corresponding hydrochlorides have been determined. The observed chemical shifts can be ascribed to charge polarization or steric effects. The latter is particularly important in establishing the axial configuration of the 4-phenyl group and 3-methyl group in the preferred conformations of α-1 and β-2, respectively, and consequently the stereochemistry of these systems. Substituent additivity effects are similar to those in the piperidones and cyclohexanes. Solvent effects on 13C resonances remove the ambiguities of conformational change suggested in earlier proton studies.

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