Carbon magnetic resonance studies of some phenyl, furyl and thienyl organometallics. Some comments on carbon-metal scalar coupling

1974 ◽  
Vol 27 (2) ◽  
pp. 417 ◽  
Author(s):  
D Doddrell ◽  
KG Lewis ◽  
CE Mulquiney ◽  
W Adcock ◽  
W Kitching ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Coupling Constant ◽  
Aryl Substituent ◽  
Magnetic Resonance Studies ◽  
Thienyl Group ◽  
13C Chemical Shift

13C chemical shift variations within a series of phenyl, furyl and thienyl Group IVB organometallics appear to be best understood in terms of the usual alkyl and aryl substituent effects on 13C chemical shifts and not variations in dπ ?pπ metal-aryl interactions. Large changes in 13C-metal scalar coupling constants have been observed suggesting that other factors besides the s-character of the carbon-metal bond is responsible in determining the coupling constant.

Origin and Nature of Transmission Modes of Anomalous Effects of meta-Substituents on the 13C Chemical Shift of the Carboxyl Carbon (δCO) of Benzoic Acid

2010 ◽  
Vol 63 (2) ◽  
pp. 321 ◽  
Author(s):  
Susanta K. Sen Gupta ◽  
Rajendra Prasad
Keyword(s):  
Chemical Shift ◽  
Benzoic Acid ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Basis Set ◽  
Benzoic Acids ◽  
Anomalous Effect ◽  
Atomic Orbitals ◽  
13C Chemical Shift ◽  
Carboxyl Carbon

Studies of substituent effects on NMR chemical shifts are of great benefit in determining fine details of electron distribution in molecules. Interestingly, NMR substituent effects are often different and even opposite to those associated with chemical reactivity. Among molecules exhibiting anomalous (reverse) substituent effects is benzoic acid, the standard model for studying substituent effects. The substituent effect on the 13C chemical shift of its carboxyl carbon (δ CO) is just the opposite of that on its acid strength or reactivity. To develop insights into the origin of the anomalous effect of a substituent on δ CO, occupancies of natural atomic orbitals at the carboxyl and ring carbons of a set of 10 meta-substituted benzoic acids have been calculated at the density functional theory level using the B3LYP function with split valance 6–311G++** basis set. Statistical correlations obtained for the 13C chemical shifts, δ CO and δ C-ring of these benzoic acids with the natural atomic orbital occupancies calculated for respective carbon atoms on one hand and with Taft’s inductive and resonance parameters (σ I and σ R BA ) of the substituents on the other hand have been critically analyzed. The findings have established firmly that a meta-substituent’s anomalous effect on δ CO is caused by the substituent-induced changes in the total occupancy of only the p z natural atomic orbitals at the carboxyl carbon. The study has demonstrated further that the transmission of the anomalous effect can be successfully interpreted by a 5.5:–2.5:1 combination of the localized, extended, and resonance-induced π-polarization effects.

35Cl AND 37Cl MAGNETIC RESONANCE OF SIMPLE CHLORINE COMPOUNDS

1965 ◽  
Vol 43 (9) ◽  
pp. 2530-2534 ◽  
Author(s):  
Yasukazu Saito
Keyword(s):  
Chemical Shift ◽  
Chemical Shifts ◽  
Quadrupole Coupling Constant ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Reference Compound ◽  
Excitation Energies ◽  
Structural Applications ◽  
Quadrupole Coupling ◽  
Magnetic Resonances

The nuclear magnetic resonances of 35Cl and 37Cl in a number of simple chlorine compounds were measured. Since both the paramagnetic contribution for chemical shift and the quadrupole coupling constant of the atom are determined by the same radial distribution of the electron, a linear relationship between the chemical shifts and the quadrupole coupling constants may be expected for compounds for which the electronic excitation energies are comparable. This was demonstrated for the series of chloro-substituted methanes. By graphical extrapolation the absolute chemical shift of the reference compound, NaCl aqueous solution, was obtained. The chemical shift of Cl− aq. ion can be interpreted as the sum of the diamagnetic shift of Cl− spherical ion and a paramagnetic shift resulting from its hydration. The experimental and theoretical values of the paramagnetic chemical shift of the Cl2 molecule were −2.06 × 10−3 and −2.17 × 10−3, respectively. Paramagnetic chemical shifts and line widths of resonance spectra of simple chlorine compounds are discussed, as well as the feasibility of high-resolution chlorine resonances for structural applications.

The relationship between carbon-13 substituent chemical shifts and proton coupling constants in aza-aromatic systems

1984 ◽  
Vol 37 (2) ◽  
pp. 311 ◽  
Author(s):  
IB Cook ◽  
S Pengprecha ◽  
B Ternai
Keyword(s):  
Experimental Data ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Proton Proton ◽  
Proton Coupling ◽  
Substituted Pyridines ◽  
Aromatic Systems ◽  
The Relationship

An equation which relates the ortho carbon-13 substituent chemical shift α-SCS in aza-aromatics to the ortho proton-proton coupling constant 3J(HH) in the corresponding carbocyclic compound is derived from experimental data. The implications for N-N bond fixation in diaza-aromatics are discussed. When the equation is applied to 2-substituted pyridines, an electronegativity parameter must be included to explain the results.

Studies of specifically fluorinated carbohydrates. Part I. Nuclear magnetic resonance studies of hexopyranosyl fluoride derivatives

1969 ◽  
Vol 47 (1) ◽  
pp. 1-17 ◽  
Author(s):  
L. D. Hall ◽  
J. F. Manville ◽  
N. S. Bhacca
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Angular Dependence ◽  
Chemical Shifts ◽  
Relative Orientation ◽  
Coupling Constants ◽  
Pyranose Ring ◽  
Spectral Parameters ◽  
Magnetic Resonance Studies ◽  
Nuclear Magnetic

A detailed study has been made of both the 1H and 19F nuclear magnetic resonance (n.m.r.) spectra of a series of hexopyranosyl fluoride derivatives. Some of the 1H spectra were measured at 220 MHz. The 1H spectral parameters define both the configuration and the conformation of each of these derivatives. Study of the 19F n.m.r. parameters revealed several stereospecific dependencies. The 19F chemical shifts depend upon, (a) the orientation of the fluorine substituent with respect to the pyranose ring and, (b) the relative orientation of other substituents attached to the ring; for acetoxy substituents, these configurational dependencies appear to be additive. The vicinal19F–1H coupling constants exhibit a marked angular dependence for which Jtrans = ca. 24 Hz whilst Jgauche = 1.0 to 1.5 Hz for [Formula: see text] and 7.5 to 12.6 Hz for [Formula: see text] The geminal19F–1H couplings depend on the orientation of the substituent at C-2; when this substituent is equatorial JF,H is ca. 53.5 Hz and when it is axial the value is ca. 49 Hz.

Studies of specifically fluorinated carbohydrates. Part II. Nuclear magnetic resonance studies of pentopyranosyl fluoride derivatives

1969 ◽  
Vol 47 (1) ◽  
pp. 19-30 ◽  
Author(s):  
L. D. Hall ◽  
J. F. Manville
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Resonance Spectroscopy ◽  
Magnetic Resonance Studies ◽  
Conformational Model ◽  
Nuclear Magnetic

Detailed studies, by 1H and 19F nuclear magnetic resonance spectroscopy, of a series of fully esterified pentopyranosyl fluorides, show that all such derivatives favor that conformer in which the fluorine substituent is axially oriented. This conclusion is supported by separate considerations of the vicinal and geminal19F–1H and 1H–1H coupling constants, of the long-range (4J) 1H–1H and 19F–1H coupling constants and of the 19F chemical shifts. The limitations of the above conformational model are discussed.

29Si-Kernresonanzuntersuchungen an N-Trimethylsilyl-substituierten Aminen und Amiden / 29Si Nuclear Magnetic Resonance Studies on N-Trimethylsilyl Derivatives of Amines and Amides

1977 ◽  
Vol 32 (2) ◽  
pp. 163-166 ◽  
Author(s):  
B. Heinz ◽  
H. C. Marsmann ◽  
U. Niemann
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Aromatic Amines ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Electronic Charge ◽  
Magnetic Resonance Studies ◽  
Basic Character ◽  
Silyl Derivatives ◽  
Trimethylsilyl Derivatives ◽  
Derivatives Of

The 29Si chemical shifts of several trimethyl silyl derivatives of amines and amides are measured and compared to other chemical and theoretical properties such as the basicities or the electronic charge on the nitrogen or the hydrogen of the N-H group of the amine or the amide. Whereas the 29Si chemical shift of saturated amines can be rationalized in terms of substituent effects, the shifts of aromatic amines show some dependency on the basic character of the amine. There seems to be little correlation between 29Si chemical shifts and electronic charge, but there is a similarity of 29Si with 1H chemical shifts of the NH group, which is interpreted as depending on anisotropy effects.

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.

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.

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