Caveat Regarding the Use of Substituent Parameters in Statistical Analyses of Molecular Properties. II. Case Study : 13 N.M.R. of 2-Substituted Pyridines and Monosubstituted Benzenes

1989 ◽  
Vol 42 (9) ◽  
pp. 1493 ◽  
Author(s):  
IB Cook
Keyword(s):  
Quantitative Analysis ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Bond Polarity ◽  
Bond Polarizability ◽  
Substituted Pyridines ◽  
Monosubstituted Benzenes ◽  
High Degree ◽  
Benzene Series

Carbon-13 n.m.r. substituent chemical shifts of equivalent positions on monosubstituted benzenes and 2-substituted pyridines are analysed by multiple linear regression on combinations of a field, resonance, electronegativity and three polarizability parameters. The ortho and meta positions of the 2-pyridine and benzene series are poorly described by σF and σR parameters, but a much improved fit is obtained when σx and/or a bond polarizability parameter σ α,(C-X) are included. The mechanism of shift formation differs markedly between the two systems when the C2, C4 and C6 positions on pyridine are compared with the geometrically equivalent positions on benzenes. Owing to the high degree of interdependence between the four substituent effects, quantitative analysis proved to be impossible. However, use of subsets of substituents with three of the four parameters approximately orthogonal enabled the mechanism to be deduced in most cases. It is postulated that the differences between the pyridine and benzene systems arises from perturbation of the C-N bond polarity. A mechanism to explain the results is presented.

Nuclear Magnetic Resonance Chemical Shifts of some Monosubstituted Isothiazoles

1975 ◽  
Vol 53 (4) ◽  
pp. 596-603 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Thomas R. Clem ◽  
Edwin D. Becker
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Charge Densities ◽  
Monosubstituted Benzenes ◽  
Proton Chemical Shifts ◽  
Nuclear Magnetic

Carbon-13 and proton chemical shifts have been measured for several monosubstituted isothiazoles. Substituent effects upon these chemical shifts are compared with those observed for monosubstituted benzenes, pyridines, and thiophenes. In general the observed substituent effects in the isothiazoles and thiophenes closely parallel one another. Correlations between the observed carbon-13 Chemical shifts and CNDO/2 calculated charge densities are examined.

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.

Substituent effects on the N.M.R. spectra of carboxylic acid derivatives. III. Correlation of 13C N.M.R. spectra of para substituted acetanilides and 4'-nitrophenyl 4-substituted benzoates with infrared carbonyl stretching frequencies, 1H N.M.R., rate and equilibrium data

1984 ◽  
Vol 37 (3) ◽  
pp. 497 ◽  
Author(s):  
CJ O'Conner ◽  
DJ McLennan ◽  
DJ Calvert ◽  
TD Lomax ◽  
AJ Porter ◽  
...  
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Linear Free Energy Relationships ◽  
Reactive Site ◽  
Linear Free Energy ◽  
Equilibrium Data ◽  
Energy Relationships ◽  
Monosubstituted Benzenes ◽  
Best Fit

The 13C n.m.r. spectra of 17 monosubstituted benzenes, 14 para substituted acetanilides and ten 4'-nitrophenyl 4-substituted benzoates have been measured in (CD3)2SO and the chemical shifts have been compared with the infrared carbonyl stretching frequencies of the substrates (in CCl4), the 1H n.m.r. chemical shifts of protons close to the reactive site of protonation, rates of hydrolysis or aminolysis and literature values of the corresponding basicity constants and rate constants. The observed substituent chemical shifts are non-additive and this result has been discussed in terms of the electronic properties of -NHCOCH3 and -COOC6H4NO2. The 13C n.m.r. and the i.r. data have been treated by single parameter and dual substituent parameter linear free energy relationships and σR values of best fit have been identified. Relative resonance and inductive contributions have been discussed.

Substituent Effects on the N.M.R. Spectra of Carboxylic Acid Derivatives. IV. 13C N.M.R. Spectra of para-Substituted Phenols, Phenylureas and Phenyl Propionates

1987 ◽  
Vol 40 (4) ◽  
pp. 677 ◽  
Author(s):  
CJ Oconnor ◽  
DJ McLennan ◽  
DJ Calvert ◽  
ASH Mitha
Keyword(s):  
Free Energy ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Single Parameter ◽  
Linear Free Energy Relationships ◽  
Substituted Phenols ◽  
Linear Free Energy ◽  
Energy Relationships ◽  
Monosubstituted Benzenes ◽  
Best Fit

The 13C n.m.r. spectra of 9 para-substituted phenols, 12 para-substituted phenylureas and 11 para-substituted phenyl propionates have been measured in (CD3)2SO and the observed substituent chemical shifts have been found to be non-additive with respect to those of the corresponding monosubstituted benzenes. The 1H n.m.r. spectra of the phenols and phenyl propionates and the i.r . carbonyl stretching frequencies of the phenyl propionates have also been determined. The spectral data have been treated by single parameter and dual substituent parameter linear free energy relationships ( l.f.e.r .) and σR values of best fit have been identified. In general, treatment by single parameter l.f.e.r . Are at least as satisfactory as those by DSP l.f.e.r.

Carbon-13 nuclear magnetic resonance spectra of E-silyl-alkenes

1980 ◽  
Vol 58 (4) ◽  
pp. 361-368 ◽  
Author(s):  
Constantinos A. Tsipis ◽  
Constantinos A. Tsoleridis
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Quantitative Analysis ◽  
Nmr Spectroscopy ◽  
Carbon Atom ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
H Nmr ◽  
Nuclear Magnetic Resonance Spectra ◽  
C Nmr

Carbon-13 nmr chemical shifts of a number of E-silyl-alkenes containing the silyl substituent at an sp2 carbon atom are presented. Assignments of the chemical shifts have been made by noting systematic variations in the spectra with changes in substituents and by comparison of the chemical shifts to those of the corresponding unsubstituted alkenes. The substituent effects observed were explained on the basis of the π-acceptor ability of the silyl substituents and the structure of the molecules. Comparing the 13C nmr spectra of the E-silyl-alkenes and those of the corresponding unsubstituted alkenes, differential chemical shifts have been obtained which can be used as empirical substituent parameters for the prediction of the 13C nmr spectra of other E-silyl-alkenes not yet studied. It was also demonstrated that 13C nmr spectroscopy can be used without resorting to special techniques (gated decoupling and the addition of paramagnetics) as an alternative method to the 1H nmr for the quantitative analysis of mixtures of regio-isomer E-silyl-alkenes.

N1s core binding energies for 2-, 3-, and 4-substituted pyridines determined by X-ray photoelectron spectroscopy. Correlations with theoretical models, substituent parameters, and gas phase basicities

1980 ◽  
Vol 58 (7) ◽  
pp. 694-703 ◽  
Author(s):  
R. S. Brown ◽  
A. Tse
Keyword(s):  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Chemical Shifts ◽  
Theoretical Models ◽  
Binding Energies ◽  
X Ray ◽  
Theoretical Approaches ◽  
Substituted Pyridines ◽  
Monosubstituted Benzenes ◽  
Gas Phase Basicities

N1s binding energies for 36 pyridines substituted at the 2-, 3-, and 4-positions have been determined by X-ray photoelectron spectroscopy. The differences in BE relative to pyridine are analysed in terms of existing theoretical approaches (electrostatic, ground potential, and relaxation potential models) and compared with [Formula: see text] values calculated for analogous monosubstituted benzenes. One finds good correlations of [Formula: see text] with solution determined σ-substituent values although some substituent values deviate from the correlation probably due to solution effects which are not present in the gas phase. Correlations between [Formula: see text] and 14N nmr chemical shifts are poor, particularly for electron withdrawing substituents. The relationship between [Formula: see text] and gas phase basicity values (ΔG0) is good, and it appears as if the [Formula: see text] is more sensitive to the substituent than ΔG0. MINDO/3 calculations on the methoxypyridines and their conjugate acids employing full geometry optimizations are presented and analysed in order to determine the effect of geometric relaxation on the gas phase basicity.

Quantitative analysis of farmer attitude towards water-saving planting structure adjustment: A case study of Heihe River middle reaches

2012 ◽  
Vol 20 (8) ◽  
pp. 1105-1112
Author(s):  
Juan WANG ◽  
Pu-Te WU ◽  
Yu-Bao WANG ◽  
Xi-Ning ZHAO ◽  
Jian-Feng SONG ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Water Saving ◽  
Heihe River ◽  
Structure Adjustment

Substituent Effects on the Basicity of ortho-, meta- and para-substituted N1,N1-Dimethyl-N2-phenylformamidines in Ethanol and in Water

1992 ◽  
Vol 57 (1) ◽  
pp. 113-118
Author(s):  
Ewa Daniela Raczyńska
Keyword(s):  
Quantitative Analysis ◽  
Aqueous Ethanol ◽  
Substituent Effects ◽  
Amino Group

The relative δpKa values of ortho-, meta-, and para-substituted N1,N1-dimethyl-N2-phenylformamidines obtained in 95.6% aqueous ethanol have been compared with those in water. The comparison shows only some differences in the ortho substituent effects. The meta and para substituent effects in ethanol are not very different from those in water. Quantitative analysis of the experimental δpKa values based on the Taft equation has led to separation of the total electromeric effects into the inductive and mesomeric effects. As compared to the amino group in anilines, the formamidine group is more sensitive to the transmission of the inductive than the mesomeric effects.

Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

1995 ◽  
Vol 60 (8) ◽  
pp. 1316-1332 ◽  
Author(s):  
Oldřich Pytela ◽  
Aleš Halama
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Intersection Point ◽  
Chemometric Analysis ◽  
Reaction Centre ◽  
Substituent Constant ◽  
Modified Method ◽  
Substituted Benzoic Acids

The paper deals with chemometric analysis of the inductive effect. The notion of inductive effect is discussed, and unambiguous definitions are given for the notions of triad: reaction centre-basic skeleton-substituent, and the therewith connected definitions of inductive effect. For a quantitative description of inductive effect 7 types of chemical models were selected including noncyclic compounds, cyclic, and bicyclic compounds, derivatives of quinuclidine, 3-substituted benzoic acids, sulfonamides and pyridines. Altogether 139 sets of experimental data from literature have been used including altogether 1 294 points (9.3 points per set, 5 points at least) reflecting substituent effects of 34 substituents. It has been found that for a standard model the dissociation of substituted bicycloalkanecarboxylic acids only is satisfactory, all the other models reflecting also the mesomeric effects to variable extent (up to 10%). A distinctly different substitution behaviour was observed with 19F and 13C NMR chemical shifts of 4-substituted 1-fluoro- or 1-methylbicyclo[2.2.2]octanes. The earlier suggested model of substituent effects based on different way of transmission of substituent effects (3 classes) has been used for separating the inductive and mesomeric effects: it is mathematically presented as a set of straight lines with the intersection point at the so-called isoeffect substituent constant. Using the modified method of conjugated deviations a chemometric scale has been created for the inductive effect which agrees very well with the conventional scales given in literature; the only differences were observed for F and CH=O substituents (which are overestimated and underestimated, respectively, in literature). In the context given the inductive effect appears as a fundamental quantity forming a basis for quantitative description of other effects transferred by electrons.

Sign in / Sign up

Export Citation Format

Share Document