Dual Substituent Parameter Equation Research Articles

Kinetics and Oxidation of Substituted Benzyl Alcohols by Phenyliodoso Acetate

Oxidation of benzyl alcohol and some meta‐ and para‐ substituted alcohols by phenyliodoso acetate (PIA) in t‐butyl alcohol–water medium (50:50) leads to the formation of corresponding benzaldehyde. The stoichiometry of the reaction was found to be 1:1. The reaction was first order each in substrate and oxidant concentrations. This reaction was studied at four different temperatures and the activation parameters were calculated. Correlation analysis was carried out using Taft’s and Swain’s dual substituent parameter (DSP) equation. The rate data of meta‐ compounds showed good correlation with (F,R) values, para‐substituted benzyl alcohols showed good correlation with σIσR+ A suitable mechanism has been proposed.

Propagation of Polar Substituent Effects in 1-(Substituted phenyl)-6,7-dimethoxy-3,4-dihydro- and -1,2,3,4-tetrahydroisoquinolines As Explained by Resonance Polarization Concept

[structures: see text] Propagation of inductive and resonance effects of phenyl substituents within 1-(substituted phenyl)-6,7-dimethoxy-3,4-dihydro- and -1,2,3,4-tetrahydroisoquinolines were studied with the aid of 13C and 15N NMR chemical shifts and ab initio calculations. The substituent-induced changes in the chemical shift (SCS) were correlated with a dual substituent parameter equation. The contributions of conjugative (rhoR) and nonconjugative effects (rhoF) were analyzed, and mapping of the substituent-induced changes is given over the entire isoquinoline moiety for both series. The experimental results can be rationalized with the aid of the resonance polarization concept. This means the consideration of the substituent-sensitive balance of different resonance structures, i.e., electron delocalization, and the effect of the aromatic ring substituents on their relative contributions. With tetrahydroisoquinolines, the delocalization of the nitrogen lone pair (stereoelectronic effect) particularly contributes. Correlation analysis of the Mulliken atomic charges for the dihydroisoquinoline derivatives was also performed. The results support the concept of the substituent-sensitive polarization of the isoquinoline moiety even if the polarization pattern achieved via the NMR approach is not quite the same as that predicted by the computational charges. Previously the concepts of localized pi-polarization and extended polarization have been used to explain polar substituent effects within aromatic side-chain derivatives. We consider that the resonance polarization model effectively contributes to the understanding of the polar substituent effects.

A proton and carbon NMR spectroscopic study of 5‐substituted acenaphthenes

The proton and carbon NMR spectra of eight 5-substituted acenaphthenes were obtained. The 13C chemical shifts of C-6 and C-2a of these compounds were compared with those of carbons located at structurally similar positions in 1-substituted naphthalenes (viz. C-8 and C-4). The 13C chemical shifts of C-2a were also analysed using the dual substituent parameter (DSP) equation. The results revealed (i) diminished steric interactions between the 5-substituent and the adjacent peri-carbon (C-6) and (ii) an enhanced transmission of both polar and resonance effects to the carbon para (C-2a) to the variable substituent, X, in acenaphthenes relative to the corresponding carbons (C-4) in 1-substituted naphthalenes. The higher ρI and ρR values observed for C-2a of acenaphthenes suggest higher polarizability in this system than in naphthalenes. AM1 calculations of charge also showed enhanced substituent effects in the case of most of the substituents in the acenaphthene system. © 1998 John Wiley & Sons, Ltd.

Effect of Substituteents on the 1H and 13C NMR Chemical Shift of trans-Pyridineacrylic and Substituted trans-Cinnamic Acids

The principles of linear free energy relationships were applied to the 1 H nmr and 13 C nmr chemical shifts induced by substituents in three isomeric trans-pyridineacrylic and substituted trans-cinnamic acids. The data for the carboxy proton chemical shift correlated well with the simple Hammett equation. Taft's dual substituent parameter equation was used for the interpretation of the balance of the inductive and resonance effects through the ethylenic bond for the C α and C β 13 C nmr shift. Using the nuclear Overhauser method, the conformation of the carboxylic group in 2-pyridineacrylic acid was determined, and its unexpected behaviour in both 1 H nmr chemical shifts;and in the previously studied reaction with diazodiphenylmethane was interpreted by the increased electron density in the π-electronic system favoured by the orbital symmetry of the part of the acid molecule

Correlation of ground and excited state dissociation constants oftrans-para- and ortho-substituted cinnamic acids

The ground and excited state dissociation constants oftrans- para- and ortho-substituted cinnamic acids have been determined in 50% (v/v) dioxan-water mixture at 30°C using the Forster cycle. The measured dissociation constants are analysed in the light of single and dual substituent parameter (DSP) equations. Excited state dissociation constants ofp-substituted cinnamic acids correlate well with the exalted substituent constants. The DSP method of analysis shows that resonance effect is predominant relative to inductive effect in the excited state than in the ground state for the para-substituted acids. The single parameter equation gives poor correlation for the ortho-substituted acids. However, the DSP analysis shows fairly good correlation. The inductive effect is predominant relative to the resonance effect in the excited state than in the ground state

Kinetics and mechanism of oxidation of organic sulphides by lead tetraacetate

Kinetics of oxidation of thirty-three organic sulphides, comprising monosubstituted aryl methyl sulphides and alkyl phenyl sulphides, by lead tetraacetate (LTA), to yield the corresponding sulphoxides, have been studied. The reaction is first order with respect to both sulphide and LTA and is catalysed by hydrogen ions. The observed solvent effect (m= 0.90 for MeSPh) is explained by a nucleophilic attack of the sulphide sulphur on LTA yielding a polar transition state. The rates of oxidation of meta- and para-substituted phenyl methyl sulphides were correlated with Taft′s and Swain′s dual substituent parameter equations. For the para-compounds, the best correlation is obtained with σ1 and σR+; the meta-substituted compounds correlate best with σ1 and σR0 values. The reaction constants are negative. The oxidation rates of ortho-substituted compounds yield an excellent correlation with a triparametric equation involving Taft′s σ1, and σR+ parameters, and Charton′s steric parameter V. The oxidation of alkyl phenyl sulphides is susceptible to both polar and steric effects of the alkyl groups. A mechanism involving formation of a sulphonium cation, in the rate-determining step, has been proposed.

Differentiation of substituent effects from hydrogen bonding and protonation effects in carbon-13 NMR spectra of pyridine N-oxides

Aromatic 13C chemical shifts are reported for 4-substituted and 3-substituted pyridine N-oxides measured in deuteriochloroform, deuterium oxide, perchloric acid (60% in D2O) and dichloroacetic acid (80% in CDCl3), and also for O-alkylated derivatives in (CD3)SO and D2O. The substituent chemical shift (SCS) data show systematic non-additivity in comparison with monosubstituted benzenes. Data for the position para to the variable substituent were analysed by means of the dual substituent parameter equation. For this position multiple substituent interactions are responsible for the non-additive shifts; interactions have both an inductive (polar) and a resonance component. Hydrogen bonding and protonation effects were differentiated from the substituent effect. It is shown that the relative 13C chemical-shift difference [(Δ3–Δ4)/Δ3] is a measure of the hydrogen bond and protonation effects and is not subject to substituent effects. 3-Dimethylaminopyridine N-oxide is protonated at the dimethylamino group, but 4-dimethylaminopyridine N-oxide at the oxygen.

Carbon‐13 and nitrogen‐15 NMR spectra of some methanesulphonanilides

AbstractThe 13C and 15N NMR spectra of some ortho‐, meta‐ and para‐substituted methanesulphonanilides were recorded. Correlations of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes were excellent and showed enhancement of the substituent effects at C‐1 (para to the substituent). The C‐1 chemical shifts were also examined by means of the dual substituent parameter (DSP) and DSP‐nonlinear resonance equations. The results indicate that the —NHSO2 Me moiety is a weak electron donor. The 15N chemical shifts of the para‐substituted compounds were analysed by means of DSP equations and the results compared with those of related compounds. Ortho‐substituted compounds indicate the high sensitivity of 15N chemical shifts towards steric compression. T1 and nuclear Overhauser enhancement data for the protonated carbons of methyl‐substituted compounds are given.

Kinetics and mechanism of the oxidation of organic sulphides by N‐chloroacetamide

AbstractThe kinetics of the oxidation of a number of monosubstituted aryl methyl, alkyl phenyl, dialkyl and diphenyl sulphides by N‐chloroacetamide (NCA) to yield the corresponding sulphoxides were studied. The reaction is first order with respect to the sulphide, NCA and hydrogen ions. There is no effect of added acetamide. Protonated NCA has been postulated as the reactive oxidizing species. The rates of oxidation of meta‐ and para‐substituted phenyl methyl sulphides were correlated with Taft's and Swain's dual substituent parameter equations. For the para‐substituted compounds, the best correlation is obtained with σI and σ; the meta‐substituted compounds correlate best with σI and σR° values. The reaction constants are negative. The oxidation rates of the ortho‐substituted sulphides yield an excellent correlation in a triparametric equation involving Taft's σI and σ values and Charton's steric parameter, V. The oxidation of alkyl phenyl sulphides is susceptible to both polar and steric effects of the alkyl group. A mechanism involving the formation of a halogenosulphonium cation in the rate‐determining step is proposed.

Studies of Tertiary Amine Oxides. Part115. Carbon - 13 nuclear magnetic resonance spectra of some N-(4-substituted phenyl) piperidine, the corresponding N-oxides, and their thermal-rearrangement product

Abstract The carbon-13 chemical shifts of seven N-(4-substituted phenyl) piperidine; the corresponding N-oxides, and their thermal rearrangement products were analyzed and assigned. The N-oxidation effect on the carbon-13 chemical shift is discussed, a correlation of N-oxidation effect with substituent constant (σp, σm, σI and σR) has been studied; dual substituent-parameter equation produce better correlation.

Mechanistic Study of the Oxidation of Substituted Benzylamines by N-Bromoacetamide

Abstract The oxidation of ortho-, meta-, and para-substituted benzylamines by N-bromoacetamide (NBA), to the corresponding benzaldehydes, is first order with respect to NBA and the amine. The pH dependence of the reaction rate suggests that the unprotonated benzylamine is the reductant. There is no effect of added acetamide. NBA itself has been postulated as the reactive oxidizing species. The oxidation of benzylamine-α,α-d2 exhibited a substantial primary kinetic isotope effect (kH⁄kD=5.81). The rates of the oxidation of the meta- and para-substituted benzylamines were separately correlated in Taft’s and Swain’s dual substituent parameter equations. For the para-substituted compounds, the best correlation is obtained with σI and σR+ values, while meta-substituted compounds correlated best with σI and σR° values. The reaction constants have negative values. The oxidation rates of the ortho-substituted compounds yield excellent correlation in a triparametric equation involving Taft’s σI and σR+ values and Charton’s steric parameter, V. A mechanism involving transfer of a hydride ion from the amine to NBA, in the rate-determining step has been proposed.

A TELLURIUM-125 STUDY OF LITHIUM ALKANE- AND ARENETELLUROLATES

Abstract Lithium alkanetellurolates and lithium arenetellurolates were prepared by reduction of ditellurides with lithium in THF. Tellurium-125 chemical shifts of lithium alkanetellurolates, RTeLi (R = Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, s-Bu and t-Bu) and lithium arenetellurolates, R'-C6H5-TeLi (R' = para-H, Me2N, MeO, Me2CHO, Me, C6H5O, F, C1, Br, Me3Si; R' = meta-MeO, EtO, Me2N, Me, F; R' = ortho-MeO and Me2N) were determined. Chemical shift trends for alkanetellurolates are compared with those previously reported for dialkyl ditellurides, dialkyl tellurides and bis(alkyltelluro)methanes. The 125Te shifts of alkanetellurolates plotted versus 77Se shifts of alkaneselenolates gave an excellent linear correlation. The substituent effects for para- and meta-substituted arenetellurolates are correlated with single- and dual-substituent parameter equations. Single parameter equations gave a poor fit, whereas dual-substituent parameter equations produced good linear correlations. The dual-substituent parameter equation of Taft is slightly better than the two-parameter equation of Swain and Lupton in correlating 125Te shifts of substituted arenetellurolates.

Kinetic Study of the Oxidation of Substituted Benzyl Alcohols by Ethyl Chlorocarbamate

Abstract The kinetics of the oxidation of twenty-four monosubstituted benzyl alcohols by ethyl chlorocarbamate (ECC) have been studied in aqueous acetic acid solution, in the presence of perchloric acid. The main product of the oxidation is the corresponding benzaldehyde. The reaction is first order with respect to the alcohol, ECC, and hydrogen ion. The oxidation of [α,α-D2]benzyl alcohol indicated a primary kinetic isotope effect, kH⁄kD=5.40 at 298 K. The value of solvent isotope effect, k(H2O)/k(D2O), is 1.85 at 298 K. Addition of ethyl carbamate does not affect the reaction rate. [EtOC(OH)NHCl]+ has been postulated as the reactive oxidizing species. The rates of oxidation of para- and meta-substituted benzyl alcohols show excellent correlation in Taft’s dual substituent parameter equation, with negative reaction constants. The rates of the ortho-substituted compounds correlate well in Charton’s equation of inductive, resonance and steric substituent parameters. A mechanism involving simultaneous transfer of a hydride ion from the C–H bond and of a proton from the O–H bond to the oxidant is proposed.

Side-chain13C nuclear magnetic resonance shifts in ring-substituted styrenes. The effect of β-substituents on β-carbon shifts

A large number of compounds of the type XC6H4–CHCYZ have been prepared and the effect of varying X, Y, and Z on the 13C n.m.r. chemical shifts of the β-(terminal) carbon of the ethenyl group has been investigated. For Y and Z constant and X meta or para to the side-chain the dominant influence is the electronic effect of X. For meta-X, excellent correlations of the Cβ shifts with Hammett σmeta constants are obtained in all cases. For para-X, there is evidence that both the inductive and resonance effect of X influence the shift with the extent of the contribution of the latter being greatest in situations where resonance interaction between X and Y/Z is expected to be strongest. Attempts to investigate the degree of this interaction by means of Taft's Dual Substituent Parameter Equation were only partly successful, and showed that in our systems such analysis is better regarded as a qualitative guide to the extent of resonance interaction that a quantitative measure of it.

Kinetics and mechanism of the oxidation of substituted benzylamines by N-chlorosuccinimide

The oxidation of ortho-, meta-, and para-substituted benzylamines by N-chlorosuccinimide (NCS), to the corresponding benzaldehydes, is first-order with respect to NCS and the amine. The pH dependence of the reaction rate suggests that the unprotonated benzylamine is the reductant. There is no effect of added succinimide. NCS itself has been postulated as the reactive oxidising species. The oxidation of [α,α-2H2]benzylamine exhibited a substantial primary kinetic isotope effect (kH/kD= 6.20). The rates of oxidation of the meta- and para-substituted benzylamines were separately correlated in Taft and Swain's dual substituent parameter equations. For the para-substituted compounds, the best correlation is obtained with σI and σR+ values; meta-substituted compounds correlate with σI and σR0 values. The reaction constants have negative values. The oxidation rates of the ortho-substituted compounds yield an excellent correlation in a triparametric equation involving Taft's σI and σR+ values and Charton's steric parameter, V. A mechanism involving transfer of a hydride ion from the amine to the oxidant in the rate-determining step is proposed.

Zur Übertragung von Substituenteneffekten in Fluorenen und Fluorenonen

On the Transmission of Substituent Effects in Fluorenes and FluorenonesA series of 2‐ and 2,7‐substituted fluorenes (1) and fluorenones (2) were prepared either by electrophilic substitution (1c–f, h–j; 2c, d, j), reduction (1, 2k, l) or nucleophilic exchange (1g, m, n; 2m) via respective diazonium compounds as well as by oxydation (2e–h, n) of the hydrocarbons (1).The carbon‐13 n.m.r. spectra for the fluorene (1a–n) and fluorenone (2a–n) derivatives was analyzed using a dual substituent parameter (DSP) equation. The substituent chemical shifts (SCS) of the carbon atoms 4a, 4b, 7 and 4a, 4b, 7, 9 of eleven fluorenes and nine fluorenones, respectively, correlate with the 𝒻, 𝓇 substituent constants and with σI, σ ones in a satisfactory manner. The comparison indicates that the correlation with the 𝒻, 𝓇 constants yields always a higher resonance contribution than the calculation with σI, σ constants. The DSP analysis reveals that transmission of the substituent effect to the substituted ring is primarily resonance controlled while the transmission to the second ring involves a π‐bond polarization mechanism. For C‐4b in the unsubstituted ring a reversed substituent effect was found. In contrast to fluorenes in fluorenones the transmission of the substituent effect involves the carbon atom 9.

15N, 31P, and 13C NMR Spectroscopy of N-Arylsulfonyl-and N-Arylcarbonyl-P,P,P-triphenylphospha-λ-Azenes. Substituent Effects and Electronic Structure

Abstract The 15N, 31P and 31C NMR spectra of several series of phospha-λ5-azenes are reported. For the N-arylsulfonyl-P,P,P-triphenylphospha-δ5-azene series (R-C6H4N-SO2-PPh3), the 31P chemical shifts, various 13C chemical shifts and 1JPN were observed to correlate linearly with the Hammett σ constants. Interestingly, the 15N chemical shifts did not correlate acceptably with any σ or with the Taft dual substituent parameter equation, and 1JPC was invariant with substituent. For the N-arylcarbonyl-P,P,P-triphenylphospha-λ5-azene series (R-C6H4-CO-N=PPh3), δ31P and various δ13C's were observed to linearly correlate with the δ constants, while δ15N, 1JPN and 1JPC correlated with both the σ and σ constants. For the N-phenyl-P,P,P-triarylphospha-λ5-azene series [Ph-N=P(C6H4-R)3] the best correlations were observed between 31P, 15N and several 13C chemical shifts and the σ constants.

Non‐additive carbon‐13 NMR substituent chemical shifts. II—1,3‐disubstituted benzenes

AbstractAromatic 13C chemical shifts are reported for an extensive set (15 common substituents) of 1,3‐disubstituted benzenes measured at low concentration in deuteriochloroform. The substituent chemical shift data show systematic non‐additivity. Data for the para‐ and two meta‐positions to the variable substituent were analysed using the recently developed non‐linear resonance (DSP‐NLR) and standard (DSP) dual substituent parameter equations. It is shown for these positions that mutual substituent interaction is responsible for the non‐additive shifts and that (a) this interaction has both an inductive (polar) and a resonance component, even for meta‐oriented substituents, and (b) the shift‐charge ratio term extends past the ipso‐position. These results are discussed in terms of local paramagnetic shielding contributions to 13C shifts.

13C NMR substituent induced chemical shifts in the side-chain carbons of α,β-unsaturated sulphones

The13C NMR chemical shifts of α,β-unsaturated sulphones of the types E-2-aryl-1-phenyl-sulphonylethylenes (series I) and E-1-arylsulphonyl-2-phenylethylenes (series II) have been measured in CDCl3 solution. The chemical shifts of the side-chain and a few ring carbons have been correlated with various single and multiparameter linear free energy relationships. Analysis of the13C NMR spectral data by a dual substituent parameter equation shows that the resonance effect is the dominant factor at C-α in series I and C-β in series II. The inductive effect is predominant at C-β in series I with a reverse substituent effect at this carbon atom. The reverse inductive contribution is explained in terms of π-polarisation mechanism.

Infrared and Raman studies of hydrogen bonded complexes involving acetone, acetophenone and benzophenone—I. Thermodynamic constants and frequency shifts of the ν OH and ν CO stretching vibrations

The hydrogen bonded complexes between phenol derivatives and acetone ( I), acetophenone ( II) and benzophenone ( III) have been studied in carbon tetrachloride solution by i.r. spectroscopy. The formation constants, the enthalpies of complex formation, the Δν OH and Δν CO values have been determined. For a given phenol derivative, the thermodynamic constants and Δν OH are ordered according to I > II > III and the influence of a substituent implanted on the phenolic ring can be expressed by the Hammett relationship. The ϱ coefficients of the Hammett equation are related to the complexation enthalpies. The Badger—Bauer relation is valid for the three bases. The comparison with complexes involving other carbonyl bases allows to precise the influence of the substituent implanted on the carbonyl group. The Δν OH values obey the dual substituent parameter equation using σ I and σ + R ; the ϱ I /ϱ R ratio is higher than one. The Δν CO values are shown to depend on the complexation enthalpy and on the delocalization effect of the substituents.