Correlation between Alkyl Cation Affinities and Proton Affinities—A Means to Rationalise Alkyl Group Substituent Effects

2000 ◽  
Vol 6 (2) ◽  
pp. 131-134 ◽  
Author(s):  
Einar Uggerud
Keyword(s):  
Linear Relationship ◽  
Alkyl Group ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Thermochemical Data ◽  
Proton Affinities ◽  
Alkyl Groups ◽  
Substituent Constants ◽  
Straight Lines ◽  
Methyl Cation

Using literature thermochemical data it is demonstrated that the known linear relationship between proton affinities and methyl cation affinities can be extended to other alkyl groups (ethyl, i-propyl, t-butyl). It is suggested that the slopes of the straight lines can be used to define a new set of alkyl substituent constants.

Kinetic Study of Hydrolysis of Benzoates. Part XXVI. Variation of the Substituent Effect with Solvent in Alkaline Hydrolysis of Substituted Alkyl Benzoates

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1557-1570 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar A. Koppel
Keyword(s):  
Kinetic Study ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Solvent Parameters ◽  
Substituent Constants ◽  
Hydrolysis Of ◽  
Main Factor

The second-order rate constants k2 (dm3 mol-1 s-1) for the alkaline hydrolysis of substituted alkyl benzoates C6H5CO2R have been measured spectrophotometrically in aqueous 0.5 M Bu4NBr at 50 and 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH, CH2C6H5, CH2CH2Cl, CH2CH2OCH3, CH2CH3) and in aqueous 5.3 M NaClO4 at 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH). The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:      ∆ log k = c0 + c1σI + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆EσI + c7∆YσI + c8∆PσI     ∆ log k = c0 + c1σ* + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆Eσ* + c7∆Yσ* + c8∆Pσ* .  ∆ log k = log kR - log kCH3. σI and σ* are the Taft inductive and polar substituent constants. E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In the data treatment ∆E = ES - EH2O , ∆Y = YS - YH2O , ∆P = PS - PH2O were used. The solvent electrophilicity, E, was found to be the main factor responsible for changes in alkyl substituent effects with medium. When σI constants were used, variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents, but twice less when σ* constants were used. The steric term for alkyl substituents was approximately independent of the solvent parameters.

Effect of Alkyl Group Structure on Cure Characteristics of N,N-Dialkylthio-Carbamyl-N′,N′-Dialkylsulfenamide Vulcanization Accelerators

1974 ◽  
Vol 47 (4) ◽  
pp. 906-910 ◽  
Author(s):  
R. D. Taylor
Keyword(s):  
Carbon Atom ◽  
Steric Hindrance ◽  
Alkyl Group ◽  
Group Structure ◽  
Substituent Effects ◽  
Steric Effects ◽  
Alkyl Groups ◽  
Inductive Effects ◽  
Cure Rates ◽  
Alpha Carbon

Abstract Wide variations in scorch times and cure rates can be attained with tetraalkylthiocabamylsulfenamides through variation in alkyl groups. Substituent effects are substantial on either the carbamate nitrogen or on the sulfenamide nitrogen. Both inductive effects and steric effects influence the scorch times and cure rates. Positive inductive effects shorten scorch times and increase cure rates. Steric hindrance at the sulfenamide nitrogen increases the scorch time. Branching at the carbon atom beta to the nitrogen has a larger effect on scorch time than branching at the alpha carbon. Thiocarbamylsulfenamides can give appreciably higher cure rates and cure efficiencies than their benzothiazole sulfenamide analogs.

scholarly journals The alkyl group is a -I + R substituent

2018 ◽  
Vol 28 (4) ◽  
Author(s):  
Luis Salvatella
Keyword(s):  
Alkyl Group ◽  
Dipole Moments ◽  
Substituent Effects ◽  
Uv Spectra ◽  
Substitution Effects ◽  
Resonance Effects ◽  
Alkyl Groups ◽  
Alkyl Substitution ◽  
Donor Substituent ◽  
Electron Donor Substituent

Electronic substituent effects are usually classified as inductive (through σ-bonds) and resonance effects (via π-bonds). The alkyl group has been usually regarded as aσ -electron donor substituent (+I effect, according to the Ingold’s classification). However, a σ-withdrawing, π-donor effect (-I + R pattern) allows explaining the actual electron-withdrawing behavior of alkyl groups when bound to sp³ carbon atoms as well as their well-known electron-releasing properties when attached to sp² or sp atoms. Alkyl substitution effects on several molecular properties (dipole moments, NMR, IR, and UV spectra, reactivity in gas phase and solution) are discussed.

Alkyl Inductive Effects on Molecular Ionization Potentials. XVI. Esters

1973 ◽  
Vol 51 (23) ◽  
pp. 3963-3965 ◽  
Author(s):  
Leonard S. Levitt ◽  
Harry F. Widing ◽  
Barbara W. Levitt
Keyword(s):  
Lone Pair ◽  
Alkyl Substituent ◽  
Ionization Potentials ◽  
Electron Loss ◽  
Average Correlation ◽  
Inductive Effects ◽  
Substituent Constants ◽  
Average Standard Error ◽  
Straight Lines ◽  
Molecular Ionization

Correlation of molecular ionization potentials, E1, with Taft's alkyl inductive substituent constants, σ1(R), has now been extended to include the esters. It is found that three series of esters, the formates, acetates, and methyl alkanoates, fall on three separate straight lines in accord with the general equation E1 = E0 + a1σ1(R), where E0 is the intercept and a1 the slope. The average standard error for the three lines is 0.024 eV with an average correlation coefficient of 0.992, showing that the alkyl substituent exerts an inductive influence on the electron density at the site suffering the electron loss: a lone pair on either the carbonyl or alkoxy oxygen atom. Evidence is deduced for the site of electron expulsion and a prediction is made concerning the site of vapor phase protonation of esters and carboxylic acids. E1 values presently not available experimentally are predicted for several esters.

17O NMR study of ortho and alkyl substituent effects in substituted phenyl and alkyl esters of benzoic acids

2011 ◽  
Vol 76 (12) ◽  
pp. 1737-1763 ◽  
Author(s):  
Vilve Nummert ◽  
Vahur Mäemets ◽  
Mare Piirsalu ◽  
Signe Vahur ◽  
Ilmar A. Koppel
Keyword(s):  
Chemical Shifts ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Ester Group ◽  
Carbonyl Oxygen ◽  
Steric Interaction ◽  
Alkyl Esters ◽  
17O Nmr ◽  
Nmr Study ◽  
Substituent Constants

17O NMR spectra for 44 ortho-, meta- and para-substituted phenyl and alkyl benzoates (C6H5CO2C6H4-X, C6H5CO2R) at natural abundance in acetonitrile were recorded. Substituent effects on the 17O NMR chemical shifts, δ(17O), of the carbonyl oxygen and the single-bonded phenoxy (OPh) and alkoxy (OR) oxygens have been studied. The δ(17O) values of the carbonyl oxygen for para derivatives showed a good correlation with the σ° constants. The δ(17O) values of carbonyl oxygen for ortho derivatives were found to be described well with the Charton equation containing the inductive, σI, resonance, σ°R, and steric, EsB, substituent constants in case the data treatment was performed separately for electron-donating +R and electron-attracting –R substituents. The electron-donating +R ortho and para substituents in substituted benzoates caused shielding and the electron-withdrawing –R substituents produced deshielding of the O signal. The steric interaction of ortho substituents with the ester group decreased the electron density at the carbonyl oxygen. In alkyl benzoates the δ(17O) values were found to be described well with the inductive, σI, and the steric, EsB, substituent constants.

Substituent effects in 1,3-indanediones

1982 ◽  
Vol 47 (5) ◽  
pp. 1486-1493 ◽  
Author(s):  
Alexander Perjéssy
Keyword(s):  
Substituent Effects ◽  
Empirical Equations ◽  
Substituent Constants ◽  
Complex Structural

The carbonyl stretching frequencies correlate well with substituent constants in a series of 166 1,3-indanediones using improved and extended Seth-Paul-Van Duyse equation. Transmissive factors and group electronegativities have been used to find empirical equations for calculation of substituent constants of more complex structural fragments.

Effects of Medium and Substituents on Dissociationof 4,4'-Disubstituted Bis(benzenesulfon)imides

1996 ◽  
Vol 61 (8) ◽  
pp. 1205-1214 ◽  
Author(s):  
Miroslav Ludwig ◽  
Pavel Štverka
Keyword(s):  
Latent Variables ◽  
Dissociation Constants ◽  
Substituent Effects ◽  
Principal Component ◽  
H Nmr ◽  
Base Process ◽  
Elemental Analyses ◽  
Substituent Constants ◽  
Model Substances ◽  
Strong Acids

Ten 4,4'-disubstituted bis(arenesulfon)imides of the general formula XC6H4SO2NHSO2C6H4X have been synthesized and their structures confirmed by their 1H NMR spectra. Elemental analyses are presented for the compounds not yet described. The dissociation constants of these model substances have been measured potentiometrically in pyridine, dimethylformamide, methanol, ethanol, propylene carbonate, acetone, acetonitrile, 1,2-dichloroethane and tetramethylene sulfone. The pKHA values obtained have been correlated with three sets of the Hammett substituent constants and the results have been used to discuss the solvent and substituent effects on the dissociation of the compounds studied. Sulfonimides with electron-acceptor substituents behave as rather strong acids in some solvents (pyridine, dimethylformamide, methanol and ethanol), whereas normal substituent dependences are found in other solvents. The experimental data have also been interpreted with the help of the statistical methods based on latent variables. From the calculations it follows that only the first principal component, which correlates well with the substituent constant sets adopted, is statistically significant in describing the substituent effect on the acid-base process studied.

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