Isokinetic correlation analysis of the series of electrophilic substitution reactions ofo-substituted phenylmercurials

Isokinetic relationships of the series of electrophilic substitution reactions ofo-substituted phenylmercurials are studied, and the results show, for the first time, that isokinetic correlation analysis can reveal the dominant factor in the system of the reactions. The analysis of S_E2 ofo-substituted phenylmercuric chlorides indicates that the steric effect ofo-substituents is the predominant factor when I₂ is used as electrophilic agent, however, the electronic effect ofo-substituents would become the predominant factor when HCl is used as the electrophilic agent. In S_E1 ofo-substituted phenylmercuric chlorides, the results of the analysis display that the predominant factor is the field effects ofo-substituents. The determination of predominant factors in those reactions would provide further scientific basis for those reaction mechanisms.     

Isokinetic correlation analysis of the series of electrophilic substitution reactions of o-substituted phenylmercurials

Isokinetic relationships of the series of electrophilic substitution reactions of o-substi-tuted phenylmercurials are studied, and the results show, for the first time, that isokinetic correlation analysis can reveal the dominant factor in the system of the reactions. The analysis of SE2 of o-substituted phenylmercuric chlorides indicates that the steric effect of o-substituents is the predominant factor when I2 is used as electrophilic agent, however, the electronic effect of o-substituents would become the predominant factor when HCI is used as the electrophilic agent. In SE1 of o-substituted phenylmercuric chlorides, the results of the analysis display that the predominant factor is the field effects of o-substituents. The determination of predominant factors in those reactions would provide further scientific basis for those reaction mechanisms.     

2,3,5,6-tetramethylmorpholine. VI. Cyclization of N-substituted 3,3′-iminobis-2-butanols

The cyclization of N-substituted 3,3′-iminobis-2-butanols to N-substituted 2,3,5,6-tetramethylmorpholines in sulfuric acid is studied. The ring closure seems to be exclusively a normal S_N2-type substitution with partial inversion of configuration before the cyclization. The steric influence of the N-substituents on the S_N2-reaction and on the inversion is discussed.     

Kinetic study of the electrophilic reaction of trialkyltin chlorides and iodine monochloride

The kinetics of the electrophilic substitution of several trialkyltin chlorides by iodine monochloride are presented. Rate constants have been determined at four different temperatures and the activation parameters A, E_a, and ΔS°⁼ are calculated. A mechanism is proposed involving charge-transfer as the driving force for the substitution. © 1993 John Wiley & Sons, Inc.     

Inherent Reactivity of Spiro-Activated Electrophilic Cyclopropanes

The kinetics of the ring-opening reactions of thiophenolates with geminal bis(acceptor)-substituted cyclopropanes in DMSO at 20 °C was monitored by photometric methods. The determined second-order rate constants of the S_N2 reactions followed linear relationships with Mayr nucleophilicity parameters (N/s_N) and Brønsted basicities (pK_aH) of the thiophenolates as well as with Hammett substituent parameters (σ) for groups attached to the thiophenolates. Phenyl-substituted cyclopropanes reacted by up to a factor of 15 faster than their unsubstituted analogues, in accord with the known activating effect of adjacent π-systems in S_N2 reactions. Variation of the electronic properties of substituents at the phenyl groups of the cyclopropanes gave rise to parabolic Hammett relationships. Thus, the inherent S_N2 reactivity of electrophilic cyclopropanes is activated by electron-rich π-systems because of the more advanced C1−C2 bond polarization in the transition state. On the other hand, electron-poor π-systems also lower the energetic barriers for the attack of anionic nucleophiles owing to attractive electrostatic interactions.     

Quantum chemical study of regioselectivity of reactions of substituted pyrido[1,2-<Emphasis Type="Italic">a</Emphasis>]benzimidazoles with electrophiles

The geometric, charge, and electronic characteristics of 7-substituted pyrido[1,2-a]benzimidazoles and their cations were calculated using the DFT method with the B3LYP functional in the 6-31G** basis set. High regioselectivity of the reactions between the condensed imidazole derivatives and electrophilic agents was explained by the results of quantum chemical simulation. It was concluded that the S _EAr reaction was orbitally controlled. According to Fukuís concept, the reaction center of the electrophilic attack was the C(8) atom of the heterocyclic system, which agreed well with the experimental data.     

The ortho effect in quantitative structure—activity correlations

A procedure for assessment of the effects of o-substituents in physical-organic systems by means of linear combination of substituent parameters is described and its applicability to various data sets on reactivity and equilibrium is shown. The procedure seems to provide a physicochemical background to the quantitative analysis of structure—activity relationships for biologically active aromatic ortho compounds. The ortho effect in biological activity is analyzed in terms of a linear combination of the electronic parameter σ_p and field-inductive F, hydrophobic π and steric E_s parameters. Depending on the type of steric effect, other parameters may be used. The model is shown to be applicable to several biological activity data sets of aromatic pesticide congeners including o-substituted derivatives.     

Selective Sulfenylative Desulfonylation or Decarbalkoxylation of α-Sulfonyl Malonates with DABCO or Bu3N: Reactivity and Conformational Analysis

The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu₃N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO₂ and CO₂R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2? and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu₃N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate.     

Aspects of tautomerism. 8. Solvolysis of some pseudo and normal acid chlorides

Pseudo acid chlorides derived from levulinic acid ando-benzoyl-benzoic acid, solvolyse in aqueous acetone, aqueous dioxane and aqueous dimethylformamide by aS _Nl process. Their reaction pattern is distinct from that of typical normal acid chlorides, viz.,p-benzoylbenzoyl chloride and fluorene-9-one-1-carboxylic acid chloride, which solvolyse by aS _N2 pathway. No evidence for tautomerism could be obtained either between the normal and pseudo forms of the acid chlorides or the derived ion pairs.     

Quantum Chemical Calculation of Conformations and Rotation Barriers of Functional Groups in Arylsulfonyl Halides

The semiempirical PM3 method is used to calculate the potential functions of internal rotation of the functional groups –SO₂Cl, –NO₂, –CH₃, –OCH₃, and –NH₂ of benzenesulfonyl halide molecules (PhSO₂Hal, Hal = F, Cl, Br, I) and twelve substituted derivatives of benzenesulfonyl chloride. Molecular conformations have been determined and internal rotation barriers of the functional groups have been calculated. For meta- and para-substituted benzenesulfonyl chlorides, the projection of the S–Hal bond is perpendicular to the plane of the benzene ring. The rotation barriers of the –SO₂Hal group of benzenesulfonyl halides increase in the series Hal = F, Cl, Br, I. The rotation barriers of the –SO₂Cl group of benzenesulfonyl chloride with meta- and para-substituents slightly increase with the electron-donor properties of the substituent. The rotation barriers of the functional groups of ortho-substituted benzenesulfonyl chlorides are 3 or 4 times as high as those of the meta- and para-isomers. For para-substituted benzenesulfonyl chlorides, the rotation barriers of the functional groups increase in the order –CH₃, –NO₂, –SO₂Cl, –OCH₃, –NH₂.     

SNAr reactions of substituted pyridines with secondary amines in aqueous solution: Kinetic and reactivity indices in density functional theory

A kinetic study is reported for the reactions of 2-methoxy-3-nitropyridine 1a and 2-methoxy-5-nitropyridine 1b with three secondary amines 2a–c (morpholine, piperidine, and pyrrolidine) in aqueous solution at 20°C. The Brønsted-type plots are linear with β_nuc = 0.52 and 0.55 for pyridines 1a and 1b , respectively, indicating that the reaction proceeds through a S_NAr mechanism in which the first step is the rate-determining step. Additional theoretical calculations using the DFT/B3LYP method confirm that the C-2 carbon being the most electrophilic center for the both pyridines 1a and 1b . The second-order rate constants have been used to evaluate the electrophilicity parameters E of 1a and 1b according to the linear free energy relationship log k (20°C) = s_N (N + E). The E parameters thus derived are compared with the electrophilic reactivities of a large variety of anisoles. The validity of these E values has been satisfactorily verified by comparison of calculated and experimental second-order rate constants for the reactions of pyridines 1a and 1b with anion of ethyl benzylacetate.     

Synthesis of N-substituted phenoxazine polymers bearing vinyl backbone

Vinyl monomers bearing N-substituted phenoxazine or 2,8-dimethylphenoxazine units were synthesized starting with the corresponding phenoxazines. N-substituents were 2-vinylbenzyl-oxycarbonylethyl group prepared via 2-carboxyethyl group, 3-methacrylamido-, 3-acrylamido-, or 3-(4-styrenesulfonamido)-propyl group prepared via 3-aminopropyl group, vinylbenzyl, or 2-vinyloxyethyl group attached by the displacements of sodium salts of the phenoxazines to the chlorides, and 2-methacryloyl- or 2-acryloyl-oxyethyl group prepared via 2-hydroxyethyl group. Free-radical polymerixations of these novel monomers proceeded smoothly, except those with 2-vinyloxyethyl group, which were susceptible to BF₃-etherate. Changes of the visible absorption spectrum of iodine in THF with addition of the monomers and polymers were considerable, with the appearance of new absorption peaks or shoulders in major cases.     

Solvent effects on the proton magnetic resonance spectra of p-substituted phenyltin chlorides

A PMR study of solvent effects on some p-substituted phenyltin chlorides (substituents = CH₃, (CH₃)₃C, CH₃O) is reported. Co-ordination of solvent molecules to the tin atom leads to an unusual low field shift of the o-ring protons. The results for p-tolytin trichloride have been compared with those for p-tolylsilyl trichloride and discussed. In o-, m- and p-tolyltin trichlorides long range spin-spin couplings between the ring methyl protons and the tin atom have been observed. The order of magnitude is o- > p- > m-methyl protons.     

Correlation of thermal analysis data and hydrolysis resistance of polycarbonates

The initial activation energy at zero conversionE _o of thermooxidative decomposition has been taken as a measure of thermal stability of polycarbonates (PC) andE _o has been correlated with the relative hydrolysis rater _h as a measure of their hydrolyse resistance. It is suggested that both decomposition processes are initiated by the same mechanism, the attack of hydrolytic agent onto ester C?O bonds. The following values ofE _o have been found: 187 (PC-M)>87 (PC-A)>43 (PC-C) kJ/mol, and they are correlated with values ofr _h being 0.01 (PC-M)<1 (PC-A)<4.4 (PC-C). It has been found, using a computer modeling technique, that bothE _o andr _h depend on the minimized energy of conformations.     

Capto-dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.     

Effects of ortho-substituents on reactivities,tacticities, and ceiling temperatures of radical polymerizations of phenyl methacrylates

Radical polymerization and copolymerization of some o-alkylphenyl methacrylates were carried out and the effect of the ortho-substituents on the ability to homopolymerize, on the monomer reactivities, and on the ceiling temperatures of the monomers was studied. The effect of the substituent on tacticities and thermal stabilities of the polymers formed was also discussed. The ability to honiopolymerize and the monomer reactivity were considerably decreased by the introduction of the o-substituent. 2,6-Di-tert-butylphenyl methacrylate formed no methanol-insoluble polymer at 60°C. On the basis of the tacticity determined it was noted that the o-substituted phenyl methacrylates preferred syndiotactic addition in the propagation reaction less than did phenyl methacrylate or methyl methacrylate. The polymers formed from the o-substituted monomers were thermally less stable than poly(phenyl methacrylate), and, consistent with this finding, ceiling temperatures of the o-substituted phenyl methacrylates seemed to be lower than that of phenyl methacrylate. The effects observed were characteristic of the o-substituents conformationally close to the carbon-carbon double bond of the monomer or the carbon carrying the unpaired electron of the polymer radical.     

Organomelemental fragmentations : I. Direct and retro fragmentations in organometallic benzyl compounds. Aromatisational metallation

Organometallic benzyl compounds are known to react with eletrophilic agents via two paths, viz., by direct substitution of the metal by the agent, and by attack of the ortho- and para-positions of the ring. The latter reaction leads to expulsion of the metal and formation of unstable triene intermediates (1-methylene-2,4-cyclohexadienes and 1-methylene-2,5-cyclohexadienes). By attributing these processes to electrophilic fragmentations (referred to as F_E) a new process may be predicted to occur, electrpohilic addition of metal salts to the exo-methylene site of trienes of this type. This process can be regarded as the reverse of the fragmentation reaction. The F_E representation proposed here forms the basis for a new organometallic synthesis, aromatisational metallation. It is shown that interaction of 1-methylene-6-ethyl-2,4-cyclohexadiene and 1-methylene-4-ethyl-2,5-cyclohexadiene with mercury dichloride in ether results in the formation of o- and p-ethylbenzylmercury chlorides, respectively.     

Halogen cleavage reactions of cis-(threo-PhCHDCHD)Mn(CO)4PEt3

Halogen cleavage reactions of $\text{cis}$-($\text{threo}$-PhCHDCHD)Mn(CO)₄, PEt₃ ($\text{3}$) are studied in detail and are found to proceed either predominantly with retention or inversion, or non-stereospecifically, depending on reaction conditions. Reaction mechanisms involving S_E2 (inversion), S_E2 (retention) and S_E (oxidative) processes are proposed, demonstrating that halogen cleavage reactions of $\text{3}$ straddle the mechanistic borderline between electrophilic substitution and oxidation processes of transition metal alkyl compounds.     

N-substituted amides of 2-cyanopenta-2E,4-dienoic acid

N-Substituted amides of 2-cyanopenta-2E,4-dienoic acid were synthesized by condensation ofN-substituted cyanoacetamides with acrolein in a dioxane-DMSO solution in the presence of Zn(OAc)₂·2H₂O as a condensing agent. X-ray diffraction study of 3-methylanilide of 2-cyanopenta-2E,4-dienoic acid (2d) demonstrated that the crystal structure of this compound is similar to that of 2-cyanopenta-2E,4-dienoic acid studied previously. However, the presence of themeta-tolyl substituent in molecule2d apparently results in the fact that the β-structure, which is typical of 2-cyanopenta-2E,4-dienoic acid, does not exist in the crystalline phase of2d. Henkel Kommanditgesellschaft auf aktien, Deutschland, D-40191 Dusseldorf, Henkelstrasse, 67. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 933–937, May, 1999.     

Electrophilic reaction of nitric oxide with Wittig reagents

Reaction of nitric oxide (NO) with p-substituted benzyl triphenylphosphonium chlorides or bromides (Wittig reagents) in CH₂Cl₂ under argon undergoes electrophilic attack of NO on the carbon center of phosphonium ylides, producing benzonitriles.