Copolymerization Reactivities of α-Substituted Crotonyl Monomers

The radical copolymerizations of various α- substituted crotonyl monomers with styrene (St) and acrylonitrile (AN) were investigated, and the copolymerization parameters were determined by a least-squares procedure reported previously. The relative reactivities of the α-substituted crotonyl monomers toward polymer radicals of St and AN were found to correlate with the equation: log (relative reactivity of CH₃CH[dbnd]CXY) = ρ (σ + σ_Y) + A(Δlog Q_x + Δlog Q_Y), where Σ and Δlog Q are the polar Hammett and resonance substituent constants, respectively, and p and A are reaction constants. From the observed straight line relationships, the values of p and A were obtained to be as follows: ρ = 0.66, A = 0.75 for attack of poly-St radical, and ρ = -3.20, A = 1.3 for attack of poly-AN radical.     

Mechanism and Linear Free Energy Relationships in Michael‐Type Addition of 4‐Substituted Anilines to Activated Olefin in Acetonitrile

Kinetic studies for the Michael‐type reactions of ethyl‐3‐(4′‐N,N‐dimethylaminophenyl)‐2‐(nonafluorobutane)sulfonylpro‐penoate 1 with 4‐X‐substituted anilines 2a–e (X = OCH₃, CH₃, H, F, and Cl) have been investigated in acetonitrile at 20°C. A quadratic dependence of the pseudo–first‐order rate constants (k_obsd) versus [ 2a–e ] has been observed and has been interpreted in terms of a dimer nucleophile mechanism. The finding of a relatively large negative ρ value (?3.09) for the Hammett plot suggests that the intermediate ( I^± ) is highly zwitterionic in nature. A linear correlation (r² = 0.9989) between the Hammett's substituent constants σ and nucleophilicity parameters N of 4‐X‐substituted anilines in acetonitrile has been observed. The electrophilicity parameters E of the olefin 1 is evaluated, using the correlations σ versus N and log k versus σ and compared with the electrophilicities of analogously Michael acceptors.     

Hammett MSP and Taft DSP analysis of substituent effects on Mulliken charges of 1‐(arylmethylene)‐1H‐cyclopropanaphthalene

Density functional theory (DFT) method is used to investigate the effects of a variety of substituents (N(CH₃)_2, OCH_3, CH₃,Br, H, F, CN, and NO₂) on Mulliken charge (Q_M) for C‐α and C‐β of 1‐(Arylmethylene)‐1H‐cyclopropanaphthalene using Hammett's mono substituent parameter (MSP) and Taft's dual substituent parameter (DSP) models. The Hammett's model approach gave statistically more significant results than the Taft's model for both carbons atoms. For the C‐α atom a reverse substituent effect was observed and attributed to localized π‐polarization. On the other hand, the MSP and DSP for the C‐β atom showed normal substituent effect. The λ value at the C‐α, explain that the resonance effects more contribution than inductive effects. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Polymerization of mono‐, Di‐, and trichloroethyl methacrylates: A study in chain transfer

Bulk free radical polymerization of the monomer series CH₂ = C(CH₃)C(O)OCH₂CH_3‐n Cl_n , n = 1, 2, 3, yields an unexpectedly crosslinked product with a crosslink density that increases with decreasing chlorine content of the respective monomer (n = 3 < n = 2 < n = 1). This chlorine substituent effect is investigated by correlation with chain transfer constant measurements for four homologous series of chloroalkyl compounds (chloroethyl acetates (CH₃C(O)OCH₂CH_3‐n Cl_n , n = 1,2,3); chloromethanes (CH_4‐n Cl_n , n = 2,3,4) and CD₂Cl₂ and CDCl₃ analogs; butyl chloride isomers (n‐ , iso‐ , sec‐, tert‐) and tert‐C₄D₉Cl analog; and nine chloroethanes (C₂H_{n ?6}Cl_n , n = 1–6)) in a methyl methacrylate polymerization. The pattern conveyed by the magnitude of chain transfer constants and deuterium isotope effects is consistent with a vicinal chlorine effect (i.e., chlorine activation of a vicinal hydrogen for abstraction) to account for the relative activities of the four series of model compounds and for the propensity of the chloroethyl methacrylates to crosslink in a bulk free radical polymerization. The chloroalkyl moiety's contribution to chain transfer is relatively modest (≤10^?4), but, when incorporated as a monomer pendant group in free radical polymerizations, it is effective in broadening molecular weight to the extent of resulting in a crosslinked polymer. Published 2016.^? J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 93–106     

Investigation of methylene group hydrogen atom reactivity in some azolidines

UV specttoscopy is used to investigate the kinetics of formation of arylidenerhodanines from rhodanine and various aromatic aldehydes whose benzene ring substitutents differ in nature and position. Hammett's equation is used to determine quantitatively the reactivities of the substituted aldehydes. The order of effect of substituent on reaction velocity is p-NO₂ > p-Cl > H > p-N(CH₃)₂, corresponding to a positive value of ρ in the Hammett equation. The position sequence is p-NO₂ > m-NO₂ > o-NO₂, and for chloro derivatives m-Cl > p-Cl, in agreement with views on transmission of inductive and conjugation effects through a benzene ring to a reaction center.     

Effects of Phenyl‐ and Methyl‐Substituents on p‐Phenylenediamine,an Electrochemical and Spectral Study

Two series of substituted p‐phenylenediamines have been studied for their electronic effects on redox potential and spectral properties. p‐Phenylenediamines and N,N,N′,N”‐tetramethyl‐p‐phenylenediamine substituted with different numbers of phenyl groups have been synthesized and their cyclic voltammograms have been obtained. The correlation between the substituent number and the redox potential appears linear. The slope reflects the additive effect of electron‐donating methyl and electron‐withdrawing phenyl groups. The absorption spectra of the cation radicals indicate that phenyl‐substituted ones have broad intervalence‐charge transfer bands. The p‐phenylenediamines exhibit different properties from triphenylamines in that the oxidized forms are more stable in CH₃CN then those in CH₂Cl₂. Some of the cation radicals or dications could undergo follow‐up chemical reactions and form products that are more easily oxidized.     

Reactions of arylnitroso oxides with substituted styrenes: Kinetics and products

The kinetics of the reactions of phenylnitroso oxide and 4-CH₃O- and 4-Cl-phenylnitroso oxides with a series of substituted styrenes (4-X-C₆H₄-CH=CH₂; X = H, CH₃O, Cl, CN) in acetonitrile at 22 ± 2°C was studied using the flash photolysis technique. It was shown for 4-CH₃O-C₆H₄NOO as an example that only the trans isomers of the nitroso oxides are involved in the reaction. There is a linear correlation between the logarithm of the rate constant and the electronic properties of the substituent in the nitroso oxide aromatic ring on the Hammett scale: ρ = 2.3 ± 0.3 (r = 0.993) for 4-CH₃O-styrene ρ = 2.03 ± 0.07 (r = 0.995) for styrene, and ρ = 1.77 ± 0.05 (r = 0.9996) for 4-Cl-styrene. Both the electron-donating and electron-withdrawing substituents in the aromatic ring of styrene increase its reactivity toward a given nitroso oxide. An analysis of the products of phenyl azide photooxidation in the presence of styrene showed that the product of phenylnitroso oxide [3+2]cycloaddition to the double bond of the olefin decomposes into benzalaniline and carbonyl oxide.     

Electrophilic bromination of gaseous aromatic compounds: Mechanism and linear free energy effects on reaction rates

Electrophilic bromination of monosubstituted aromatic compounds is effected in a pentaquadrupole mass spectrometer using BrCO⁺ and CH₃NH₂Br⁺ as mass-selected reagent ions. Reaction normally occurs at the ring and the brominated product can be mass selected in turn and caused to dissociate by Br˙ loss upon collision-induced dissociation. Linear free energy correlations with Brown substituent σ⁺ constants describe the extent of gas-phase bromine cation addition under the non-equilibrium, low-pressure and solvent-free conditions which pertain in quadruple collision cells. The electrophilic addition reaction proceeds via a σ-complex to the ring as suggested by MS³ spectra, except in the case of nitrobenzene, where substituent bromination is suggested by the occurrence of a competitive process in which the nitrosubstituent is displaced by bromine. The reactivity parameters ρ are ?0.23 and ?0.56 for the gaseous reagents, BrCO⁺ and CH₃NH₂Br⁺, respectively. Both values are much less negative than corresponding values for bromination in solution. The greater reactivity of BrCO⁺ is evident by the fact that it reacts even with the strongly deactivated substrates and this is consistent with a weak Br? CO bond. Competitive protonation occurs in the case of CH₃NH₂Br⁺ and, unlike bromination, the rate of this reaction does not correlate with σ⁺ values. This is suggested to be a consequence of protonation at the ring in some cases and at the substituent in others, including acetophenone and benzonitrile. Evidence for this is that, in contrast to its lack of correlation with substituent constants, the rate of protonation correlates linearly with proton affinity.     

Relation between the Length of the Transannular Bond Si←N in 1-Substituted Silatranes and the Inductive Effect of Substituents at the Silicon Atom

A strict linear correlation is found between the length of the coordination bond Si-N in 1-substituted silatranes XCH₂Si(OCH₂CH₂)₃N and the inductive constant _I of substituent XCH₂. This equation is also valid for other compounds of the RSi(OCH₂CH₂)₃N type, in which silicon is bound to an sp ²-carbon atom (R = CH = CH₂, Ph, 2-furyl, 2-thienyl, etc.). The deduced correlation equation allows determination of earlier unknown and refinement of existing _4I constants of substituents R on the basis of X-ray diffraction Si-N bond lengths in silatranes RSi(OCH₂CH₂)₃N. Deviations from the correlation point to noninductive interaction between substituent R and the silantranyl group (R = R'O). The bond length in 1-fluorosilatrane nicely fits the deduced equation.     

Prediction of Physical Properties of Dimethacrylate Polymer Networks by a Group Contribution Approach

In this work, the correlation between experimental and theoretical values of density (ρ) and glass transition temperature (T _g ) of dimethacrylate polymer networks is elaborated. The developed methodologies are based on the additive principle of the known monomer chemical structures. The predicted values of ρ differed by a maximum of 1% from the experimental values. The methodology developed for T _g prediction is based on the assumption that dimethacrylate structural units are treated as main chains between ?CH₂C(CH₃)? tri-functional volumeless cross-links. Three-quarters of the calculated T _g values differed less than 20 K from the experimental ones.     

Theoretical study of the effects of substitution,solvation, and structure on the interaction between nitriles and methanol

We report an investigation on intermolecular interactions in R? CN ··· H? OCH₃ (R = H, CH₃, F, Cl, NO₂, OH, SH, SCH₃, CHO, COCH₃, CH₂Cl, CH₂F, CH₂OH, CH₂COOH, CF₃, SCOCH₃, SCF₃, OCHF₂, CH₂CF₃, CH₂OCH₃, and CH₂CH₂OH) complexes using density functional theory. The calculations were conducted on B3LYP/6‐311++G** level of theory for optimization of geometries of complexes and monomers. An improper hydrogen bonding (HB) in the H₃CO? H ··· NC? R complexes was observed in that N atom of the nitriles functions acts as a proton acceptor. Furthermore, quantum theory of “Atoms in Molecules” (AIM) and natural bond orbital (NBO) method were applied to analyze H‐bond interactions in respective complexes. The electron density (ρ) and Laplacian (?²ρ) properties, estimated by atoms in molecules calculations, indicate that H ··· N bond possesses low ρ and positive ?²ρ values, which are in agreement with partially covalent character of the HBs, whereas O? H bonds have negative ?²ρ values. In addition, the weak intermolecular force due to dipole–dipole interaction (U) is also considered for analysis. The examination of HB in these complexes by quantum theory of NBO method fairly supports the ab initio results. Natural population analysis data, the electron density, and Laplacian properties, as well as, the ν(O? H) and γ(O? H) frequencies of complexes, calculated at the B3LYP/6‐311++G** level of theory, are used to evaluate the HB interactions. The calculated geometrical parameters and conformational analysis in water phase solution show that the H₃CO? H ··· NC? R complexes in water are more stable than that in gas phase. The obtained results demonstrated a strong influence of the R substituent on the properties of complexes. Numerous correlations between topological, geometrical, thermodynamic properties, and energetic parameters were also found. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Transfer gibbs free energies from H2O to CH3OH for a series of substituted phenyltropylium ions,Malachite Green,and Crystal Violet

The solubilities of the perchlorate salts of phenyltropylium,para-methoxyphenyltropylium, andpara-dimethylaminophenyltropylium and the fluoroborate salts of Malachite Green and Crystal Violet have been determined in H₂O and CH₃OH. From these data the transfer Gibbs free energies from H₂O to CH₃OH have been calculated and compared to the predictions of Ritchie and Virtanen. The introduction of a dimethylamino substituent in thepara position of the phenyl ring substantially increases the relative stability of the cations in CH₃OH compared to H₂O. This observation is accounted for in terms of London dispersion forces.To whom correspondence should be addressed.     

Linear dependence of the intensity of the [M + H]+ ion peak in fast atom bombardment mass spectrometry on the basicity of meso-substituted octaethylporphyrins

A fast atom bombardment mass spectrometric study of the meso-substituent effect of Octaethylporphyrins (OEPX, X = NH₂, CH₃, H, CHO, Cl, CN, NO₂) is reported. The intensity of the [M + H]⁺ ion peaks was estimated quantitatively using an external standard, which was observed to be correlated linearly with the basicity (pK₃) of the OEPX. The pK₃ value of the OEPXs was obtained by titration with perchloric acid and it was observed to be correlated linearly with Hammett's σ_p value, with a ρ value of 1.38.     

Carbon-13 NMR study of substituted benzyl N,N-dimethylcarbamates

The ¹³C NMR chemical shifts of m- and p-substituted benzyl N,N-dimethylcarbamates were measured in CDCl₃. The meta and para ¹³C substituent chemical shifts were analysed by means of dual substituent parameter (DSP) equations. Good correlations were obtained, especially for the para-carbon substituent chemical shifts. The computed transmission coefficients, ρ_I and ρ_R, are consistent with the general features of the fitting parameters. It has been shown that no significant electron demand is imposed by the ? CH₂OCON(CH₃)₂ substituent.     

Ion-neutral complexes resulting from dissociative protonation: Fragmentation of <Emphasis Type="Italic">α</Emphasis>-furanylmethyl benzyl ethers and 4-<Emphasis Type="Italic">N,N</Emphasis>-dimethylbenzyl benzyl ethers

The loss of CH₂O during mass spectrometry in two series of α-aromaticmethyl benzyl ether compounds, namely, α-furanylmethyl p-substituted-benzyl ethers and 4-N,N-dimethylbenzyl p-substituted-benzyl ethers, is particularly interesting. The fragmentation mechanism is proposed to involve an ion-neutral complex-mediated pathway. Specifically, before the formation of an ion-neutral intermediate, the proton is transferred from the thermodynamically favored site at either the ether oxygen atom or the nitrogen atom to the dissociative protonation site at C_α position in either the furyl group or the 4-N,N-dimethylphenyl group. This transfer has been clarified via computational studies and isotopically labeled experiments. In addition, the decomposition of the intermediate may be affected by the substituent groups on the phenyl ring. This conclusion is indicated by the reasonably good correlation between ln[([M + H − CH₂O]⁺)/([M + H − CH₂O − C₆H₅R]⁺)] and the substituent constants.     

Chemical Detoxification of Organomercurials

Organomercurials including methylmercury are ubiquitous environmental pollutants and highly toxic to humans. Now it could be shown that N‐methylimidazole based thiones/selones having an N‐CH₂CH₂OH substituent are remarkably effective in detoxifying various organomercurials to produce less toxic HgE (E=S, Se) nanoparticles. Compounds lacking the N‐CH₂CH₂OH substituent failed to produce HgE nanoparticles upon treatment with organomercurials, suggesting that this moiety plays a crucial role in the detoxification by facilitating the desulfurization and deselenization processes. This novel way of detoxifying organomercurials may lead to the discovery of new compounds to treat patients suffering from methylmercury poisoning.     

Electrochemistry of Nitrated N‐Confused Free‐Base Tetraaryl‐Porphyrins in Nonaqueous Media

Four nitrated N‐confused free‐base tetraarylporphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media. The examined compounds are represented as NO₂(Ar)₄NcpH₂, where NO₂(Ar)₄Ncp is the dianion of a tetraaryl N‐confused porphyrin with an inner carbon bound NO₂ group and Ar is a p‐CH₃OPh, p‐CH₃Ph, Ph or p‐ClPh substituent on each meso‐position of the macrocycle. UV/Vis spectra and NMR spectroscopy data indicate that the same form of the porphyrin exists in CH₂Cl₂ and DMF which is unlike the case of non‐NO₂ N‐confused porphyrins. The Soret band of NO₂(Ar)₄NcpH₂ exhibits a 30–36 nm red‐shift in CH₂Cl₂ and DMF as compared to the spectrum of the non‐NO₂ N‐confused porphyrins. The first two reductions and first oxidation of NO₂(Ar)₄NcpH₂ are reversible in CH₂Cl₂ containing 0.1 M TBAP. The measured HOMO–LUMO gap averages 1.65 V in CH₂Cl₂ and 1.53 V in DMF, with both values being similar to those of the non‐NO₂ substituted compounds. The nitro group on the inverted pyrrole is itself not reduced within the negative potential limit of CH₂Cl₂ or DMF, but its presence significantly affects both the UV/Vis spectra and redox potentials.     

Substituent effects on the disproportionation-combination rate constant ratios for gas-phase halocarbon radicals. II. Reactions of •CF3 +CF3CH2CH2• and CF3CH2CH2• + CF3CH2CH2•

Disproportionation/combination rate constant ratios, k_d /k_c, have been measured for the collision between CF₃CH₂CH₂ and CF₃ radicals to be 0.022 ± 0.002 and for CF₃CH₂CH₂ and CF₃CH₂CH₂ radicals to be 0.100 ± 0.002. Comparison to previous work from this laboratory for the reaction of CF₃CH₂CHCl with CF₃ radicals shows that substitution of Cl for H increases the k_d /k_c by about 50%; however, for the auto disproportionation-combination of CF₃CH₂CH₂ radicals the chlorine substituent decreases the observed rate constant ratio by a factor of two. The chlorine substituent effect on the observed k_d /k_c ratios is compared to predictions from molecular orbital calculations. © 1996 John Wiley & Sons, Inc.