The application of the Hammett equation to 13C N.M.R. spectroscopy: correlations in the β-nitrostyrenes

1976 ◽  
Vol 29 (12) ◽  
pp. 2607 ◽  
Author(s):  
DAR Happer
Keyword(s):  
Chemical Shift ◽  
Convenient Method ◽  
Experimental Error ◽  
Dimethyl Sulphoxide ◽  
Hammett Equation ◽  
Excellent Correlation ◽  
Substituent Constants ◽  
Hammett Σ Constants

A series of 33 β-nitrostyrenes has been prepared and their 13C N.M.R. spectra have been determined in dimethyl sulphoxide and in deuterochloroform (where soluble). Hammett correlations between substituent and the chemical shift of both the para ring carbons and the α-carbon of the ethenyl group have been shown to be only approximate. In contrast, an excellent correlation has been observed between the chemical shift of the β-carbon of the ethenyl group and Hammett σ+ constants in all cases except those involving para substituents capable of exerting a - R effect. Possible reasons for this are considered. The system appears to be the first reported one where 13C measurements for both meta- and para-substituted compounds give rise to correlations in which agreement lies well inside the limits of experimental error, and shows promise as a convenient method for calculating substituent constants and studying their variation with solvent.

CuAAC and RuAAC with Alkyne-functionalised Dihydroazulene Photoswitches and Determination of Hammett σ-Constants for Triazoles

2014 ◽  
Vol 67 (3) ◽  
pp. 531 ◽  
Author(s):  
Henriette Lissau ◽  
Søren Lindbæk Broman ◽  
Martyn Jevric ◽  
Anders Ø. Madsen ◽  
Mogens Brøndsted Nielsen
Keyword(s):  
Molecular Electronics ◽  
Ring Closure ◽  
Reference Systems ◽  
Rigid Structure ◽  
Useful Components ◽  
Substituent Constants ◽  
Hammett Σ Constants

Dihydroazulene (DHA)–vinylheptafulvene (VHF) photoswitches have attracted attention as potentially useful components in molecular electronics. The π-conjugated dihydroazulene system is a rigid structure and can be strategically functionalised to place handles for further elaboration. Here we show that alkyne-functionalised dihydroazulenes can be subjected to copper and ruthenium catalysed azide–alkyne cycloadditions (CuAAC and RuAAC) with tolylazide, furnishing 1,4- and 1,5-disubstituted triazoles. The rates of ring-closure of the corresponding vinylheptafulvenes were compared with those of reference systems, which allowed determination of Hammett substituent constants (meta and para) for N-tolyl-substituted 1,2,3-triazoles.

Aromatic amides. IX. Temperature effects on the N.M.R. spectra of substituted acetanilides

1974 ◽  
Vol 27 (12) ◽  
pp. 2617 ◽  
Author(s):  
ID Rae
Keyword(s):  
Hydrogen Bond ◽  
Chemical Shift ◽  
Benzene Ring ◽  
Intramolecular Hydrogen Bond ◽  
Temperature Effects ◽  
Dimethyl Sulphoxide ◽  
Intramolecular Hydrogen ◽  
Strong Intramolecular Hydrogen Bond ◽  
Ortho Substituent

N.m.r. spectra have been measured for several anilides in dimethyl sulphoxide solution for temperatures in the range 40-140�. The change of the N-H chemical shift with temperature depends on the nature of the ortho substituent on the benzene ring, being least when a strong intramolecular hydrogen bond is possible between the amide N-H and the ortho substituent. For 2?-nitroanilides, the 6?- proton becomes increasingly deshielded as the temperature is raised.

Effect of para Substitution on Dissociation of N-Phenylbenzenesulfonamides

2004 ◽  
Vol 69 (7) ◽  
pp. 1479-1490 ◽  
Author(s):  
Martin Mansfeld ◽  
Patrik Pařík ◽  
Miroslav Ludwig
Keyword(s):  
Elemental Analysis ◽  
Principal Components ◽  
Latent Variables ◽  
Dissociation Constants ◽  
Additive Model ◽  
Reaction Centre ◽  
Hammett Equation ◽  
Substituted Anilines ◽  
Transmission Effect ◽  
Substituent Constants

The reaction of substituted anilines and benzenesulfonyl chlorides has been used to prepare 49 substituted N-phenylbenzenesulfonamides of general formula 4-X-C6H4SO2NHC6H4-Y-4'. Their purity was checked by elemental analysis. The substituents X and Y include H, CH3, CH3O, Cl, Br, CN, and NO2. The dissociation constants of all compounds were determined by potentiometric titration in methanol, acetonitrile, N,N-dimethylformamide, and pyridine. The obtained dissociation constants, pKHA, were correlated with various sets of substituent constants. It was found that the effects of substituents X and Y on the dissociation are best described by using the Hammett equation with σp constants and the Yukawa-Tsuno equation with σp- and σp constants, respectively. This result confirms the direct conjugation of Y substituent with the reaction centre. The explained variability using the additive model was above 96% in all the solvents used. The data also provided information about the transmission effect of the SO2 group. The average dissociation constants were further processed by the latent variables methods, principal components and conjugated deviations analyses.

scholarly journals Benzyloxycarbonylprolylprolinal, a transition-state analogue for prolyl oligopeptidase, forms a tetrahedral adduct with catalytic serine, not a reactive cysteine

1997 ◽  
Vol 322 (3) ◽  
pp. 839-843 ◽  
Author(s):  
Ara KAHYAOGLU ◽  
Khadijeh HAGHJOO ◽  
Ferenc KRAICSOVITS ◽  
Frank JORDAN ◽  
Laszlo POLGAR
Keyword(s):  
Chemical Shift ◽  
Chemical Modification ◽  
Transition State ◽  
Molecular Mass ◽  
Serine Protease ◽  
13C Nmr ◽  
Dimethyl Sulphoxide ◽  
Tetrahedral Complex ◽  
Prolyl Oligopeptidase ◽  
Transition State Analogue

N-Benzyloxycarbonyl-l-prolyl-l-[1-13C]prolinal was synthesized starting with reduction of l-[1-13C]Pro to l-[1-13C]prolinol, followed by coupling with N-benzyloxycarbonyl-l-Pro to N-benzyloxycarbonyl-l-Pro-l-[1-13C]prolinol (Z-Pro-[1-13C]prolinol), and finally oxidation of the alcohol to the aldehyde with dimethyl sulphoxide. While the 13C NMR chemical shift of the aldehyde carbon is 202 p.p.m., that of the aldehyde hydrate is between 91.6 and 91.8 p.p.m., that of the dithiothreitol adduct is between 74.8 and 75.0 p.p.m., and that in the presence of the serine protease prolyl oligopeptidase is at 92.3 p.p.m.. The linewidth of the latter is 114 Hz, roughly consistent with the molecular mass of 80 kDa reported for the enzyme. Inverse detection experiments gave a 1H resonance at 5.29 p.p.m. with a linewidth of 80 Hz, also consistent with the expected chemical shift and linewidth for a hemiacetal bound to such a large enzyme, while the free hydrate gave resonances at 5.18 and 5.25 p.p.m., with very much narrower linewidths. It is concluded that Z-Pro-prolinal, a putative transition-state analogue for prolyl oligopeptidase, forms a tetrahedral complex with the enzyme at its catalytic serine, rather than at a neighbouring cysteine that was found to be highly reactive according to chemical modification studies.

THE INHIBITED AUTOXIDATION OF STYRENE: PART II. THE RELATIVE INHIBITING EFFICIENCIES OF META- AND PARA-SUBSTITUTED PHENOLS

1963 ◽  
Vol 41 (7) ◽  
pp. 1744-1751 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Abstraction ◽  
Excellent Correlation ◽  
Substituted Phenols ◽  
Substituent Constants

The relative rates of reaction of 11 meta- and para-substituted phenols with styrylperoxy radicals have been measured at 65 °C and have been shown to give an excellent correlation with electrophilic substituent constants. The reaction is compared with a number of similar hydrogen abstraction reactions.

Field and Resonance Components of Substituent Effects in Relation to the Hammett Equation

1972 ◽  
Vol 50 (7) ◽  
pp. 1030-1035 ◽  
Author(s):  
L. D. Hansen ◽  
L. G. Hepler
Keyword(s):  
Substituent Effects ◽  
Similar Reaction ◽  
Hammett Equation ◽  
Reaction Series ◽  
Field Interaction ◽  
Isokinetic Relationship ◽  
Resonance Effects ◽  
Transmission Coefficients ◽  
Substituent Constants ◽  
Specific Reactions

Following Swain and Lupton's analysis of substituent effects, we have taken ΔG0 = aete + artr for a typical substituent effect reaction. In this equation ae and ar are substituent constants for electrostatic field and resonance effects while te and tr are corresponding transmission coefficients. Both substituent constants and tr are taken to be independent of solvent and temperature, while te is taken to depend on both solvent and temperature. General conclusions based on analysis of this model are the following. (i) A Hammett ρσ equation with constant σ values that are valid over a range of temperatures for a variety of reactions in several solvents can be obtained only when either the field or the resonance interaction is negligible compared with the other. (ii) A Hammett ρσ equation can be expected to hold for "similar" reaction series in a given solvent at one temperature even when both the field and resonance interactions are important, (iii) An isoequilibrium or isokinetic relationship can be expected only when the field interaction is dominant.The general equations leading to these and other conclusions are presented so that one can later insert appropriate mathematical descriptions of detailed models and thereby obtain information about specific reactions.

Chemometrical Analysis of Substituent Effects. IV. Additivity of Substituent Effects in Dissociation of 3,5-Disubstituted Benzoic Acids in Organic Solvents

1994 ◽  
Vol 59 (7) ◽  
pp. 1637-1644 ◽  
Author(s):  
Oldřich Pytela ◽  
Jiří Kulhánek ◽  
Miroslav Ludwig
Keyword(s):  
Organic Solvents ◽  
Dissociation Constants ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Specific Solvation ◽  
Reaction Constant ◽  
Substituent Constants ◽  
The Individual

Ten 3,5-disubstituted benzoic acids have been synthesized containing all possible combinations of the following substituents: CH3O, CH3, Cl/Br, NO2. The dissociation constants of these acids have been measured in seven organic solvents (methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, 1,2-dichloroethane). It has been found that the effect of disubstitution is smaller than that due to interaction of substituents or their solvation and represents only about 0.2% of the effect caused by the individual substituents. The additivity in 3,5-disubstitution is about 2 - 3 times as good as that in 3,4-disubstitution. The quantitative description of substituent effects at the 3 and 5 positions is additive within the range of validity of the Hammett equation irrespective of the type of the substituent constants adopted, the addition of the multiplicative term being statistically insignificant. The solvent effect on 3,4- and 3,5-disubstituted derivatives is somewhat different at the same value of the reaction constant, due predominantly to the specific solvation of the 4-CH3O and 4-NO2 groups.

Serotonine-Nucleotide Interaction Studied by PMR. Explanation of the Variability in Association Constants Obtained from Chemical Shifts of Different Protons

1974 ◽  
Vol 29 (9-10) ◽  
pp. 488-492 ◽  
Author(s):  
R Lawaczeck ◽  
K Wagner
Keyword(s):  
Computer Simulation ◽  
Chemical Shift ◽  
Significant Variation ◽  
Experimental Error ◽  
Chemical Shifts ◽  
Association Constants

Abstract A study of the association of serotonine with 5'-AMP by PM R spectroscopy is described. The association constants obtained from the chemical shift of non-equivalent protons show considerable variation outside experimental error, a fact which wT as reported by several authors. To support the suppositon that small amounts of complexes of different stoichiometry, — which in general can hardly be detected — , are responsible for this phenomenon, computer simulation of various hypo­ thetical systems were investigated. The results clearly demonstrate that the neglect of minor fractions of complexes of different stoichiometries lead to significant variation in the association constants calculated for different protons, provided that these protons experience different magnetic enviro-ments in the different complexes.

scholarly journals A convenient method for lactonization of α-allyl esters using iodine in dimethyl- sulphoxide

2014 ◽  
Vol 28 (3) ◽  
pp. 469 ◽  
Author(s):  
B. R. Nawghare ◽  
S. V. Gaikwad ◽  
B. V. Pawar ◽  
P. D. Lokhande
Keyword(s):  
Convenient Method ◽  
Dimethyl Sulphoxide ◽  
Allyl Esters
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