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.

Substituent effects in naphthalene. II. The strengths of the 4, 5, 6, 7, and 8-substituted 2-naphthoic acids

1965 ◽  
Vol 18 (9) ◽  
pp. 1365 ◽  
Author(s):  
PR Wells ◽  
W Adcock
Keyword(s):  
Electrostatic Interactions ◽  
Aqueous Ethanol ◽  
Substituent Effects ◽  
Simple Expression ◽  
Dipole Orientation ◽  
Aromatic Substituent ◽  
Resonance Effects ◽  
Naphthoic Acid ◽  
Inductive Effects ◽  
Substituted 1

The apparent pKa values of 44 substituted 2-naphthoic acids, six substituted 1-naphthoic acids, and the unsubstituted naphthoic acids have been determined for 50% v/v aqueous ethanol at 25�. The ΔpK values are examined in terms of Dewar and Grisdale's simple expression for aromatic substituent effects. This expression proves to be fairly satisfactory, but takes no account of substituent dipole orientation, secondary resonance effects, nor π-inductive effects. A survey of the naphthoic acid strengths demonstrates the importance of these factors. In particular, unambiguous evidence for the important role played by direct electrostatic interactions is obtained.

Substituent effects at silicon in cations SiX+, HSiX+•, and H2SiX+, and in radicals H2SiX+•

1989 ◽  
Vol 67 (6) ◽  
pp. 991-997 ◽  
Author(s):  
A. C. Hopkinson ◽  
M. H. Lien
Keyword(s):  
Linear Relationship ◽  
Molecular Orbital ◽  
Single Point ◽  
Substituent Effects ◽  
Molecular Orbital Calculations ◽  
Amino Group ◽  
Ionisation Potential ◽  
Silyl Radicals

Abinitio molecular orbital calculations at the 6-31G* level have been used to optimise structures for ions SiX+, HSiX+•, and H2SiX+, and for neutrals HSiX (singlets), H2SiX•, and H3SiX, where X is H, CH3, NH2, OH, F, CN, and NC. Single point calculations at the MP4(SDTQ)/6-31G* level were used to calculate substituent stabilisation energies.The amino group is the strongest π-donor and also is the most stabilising group in the cations, the silylenes, and the silyl radicals. Stabilisation is greatest in ions SiX+. Ions HSiX+• and H2SiX+ are stabilised by similar but smaller amounts, although CN and NC are destabilising in these ions. Substituent stabilisation energies in radicals H2SiX• are almost zero. There is a linear relationship between the stabilisation energies of ions H2SiX+ and the ionisation potentials of radicals H2SiX•, but a similar plot correlating stabilisation energies for ions HSiX+۟• with the ionisation potential of HSiX (singlet) shows considerable scatter. Keywords: silications, silyl radicals, stabilisation energies.

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.

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.

Phosphoryl to carbonyl migration of amino groups in mixed anhydrides

1986 ◽  
Vol 64 (9) ◽  
pp. 1702-1708 ◽  
Author(s):  
Jill Symes ◽  
Tomasz A. Modro
Keyword(s):  
Transition State ◽  
Lewis Acids ◽  
Reaction Rate ◽  
Functional Group ◽  
Substituent Effects ◽  
Activation Parameters ◽  
Amino Group ◽  
Amino Groups ◽  
Group Transfer ◽  
Mixed Anhydrides

Mixed anhydrides derived from carboxylic and amidophosphoric acids, (RO)(R′2N)P(O)OC(O)R″ (1), undergo unimolecular fragmentation yielding carboxyamides, R″C(O)NR′2, and metaphosphate esters, ROPO2. The mechanism of the amino group transfer was studied for substrate 1a (1, R = R′ = Me; R″ = Ph); solvent as well as substituent effects indicate little (if any) charge development in the transition state. The effects of solvents and Lewis acids on the reaction rate and the activation parameters determined for 1a can be explained best in terms of stabilizing interactions with either carboxyamide or metaphosphate being formed in the course of reaction. The transfer of a functional group from one acyl center to another was investigated for other anhydride systems and the relative contributions of the fragmentation vs. disproportionation of substrates are discussed.

RING-PROTON CHEMICAL SHIFTS OF SOME SUBSTITUTED ANILINES IN CARBON TETRACHLORIDE AND TRIFLUOROACETIC ACID

1963 ◽  
Vol 41 (9) ◽  
pp. 2339-2345 ◽  
Author(s):  
W. F. Reynolds ◽  
T. Schaefer
Keyword(s):  
Carbon Tetrachloride ◽  
Steric Hindrance ◽  
Trifluoroacetic Acid ◽  
Electronic Spectra ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Amino Group ◽  
Substituted Anilines ◽  
Ring Proton ◽  
Proton Chemical Shifts

The chemical shifts of the ring-proton spectra of a series of substituted anilines are reported relative to internal benzene in the solvents carbon tetrachloride and trifluoroacetic acid. The substituent parameters in cyclohexane derived by Martin can be used together with our parameters for the para-fluoro and -ammonio (NH3+) groups to demonstrate additivity of the substituent effects in both carbon tetrachloride and trifluoroacetic acid. The somewhat puzzling ring-proton shifts in the latter solvent are attributed to counterion effects arising from a juxtaposition of the two centers of charge. Steric hindrance to π-overlap of the amino group with the ring is demonstrated in certain cases and a parallel behavior is found between the ring-proton shifts and the electronic spectra of these molecules.

Substituent effect on solvolysis of 3-acetyl-1,3-diphenyltriazenes

1984 ◽  
Vol 49 (5) ◽  
pp. 1173-1181 ◽  
Author(s):  
Oldřich Pytela ◽  
Miroslav Pilný ◽  
Miroslav Večeřa
Keyword(s):  
Reaction Mechanism ◽  
Rate Constant ◽  
Substituent Effect ◽  
Aqueous Ethanol ◽  
Substituent Effects ◽  
Point Of View ◽  
Kinetics Of

Eleven symmetrically disubstituted 3-acetyl-1,3-diphenyltriazenes have been synthetized by anew method. The solvolysis kinetics of the title compounds has been measured in 20% aqueous ethanol at several temperatures. The results are discussed from the point of view of temperature and substituent effects on the solvolysis rate constant of the 3-acetyl-1,3-diphenyltriazenes and conclusions are drawn about the reaction mechanism.

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