Copolymerizations of 2-hydroxyethylmethacrylate with vinylpyridines and with N-substituted methacrylamides

Studies were made of the copolymerizations of 2-hydroxyethylmethacrylate with 2-, 3- and 4-vinylpyridine. N-(trans-4′-nitro-4-stilbenyl)methacrylamide and N-(trans-4-stilbenyl)methacrylamide. Methods of Fineman-Ross, Joshi-Joshi, Tidwell-Mortimer and Tosi were employed to determine monomer reactivity ratios; the results for 2- and 4-vinylpyridine were compared with those calculated from the Q-e scheme. The monomer reactivity ratios for 2-hydroxyethylmethacrylate with vinylpyridines calculated by different methods showed good agreement. The monomer reactivity is briefly discussed.     

Reactivity of cis dichlorodiammineplatinum(II) (cisplatin) toward selected nucleophiles

Results are reported for the reaction of cis-dichlorodiammineplatinum(II) (“cisplatin”) with various nucleophiles in aqueous solution at constant ionic strength (μ = 0.5) and 30°C. The reactivity is described in terms of linear free energy relationships between the logarithm of the second order rate constants and two established indices of nucleophilicity, i.e. electrode potentials, E° and nucleophilic reactivity constants, n_Pt^o (based on reactivity of trans-[Pt(PY)₂Cl₂] in methanol). New nucleophilic reactivity constants, (n_Pt^o)′are reported based on “cisplatin” reactivity in water.     

Influence of acyl groups on glucopyranoside reactivity in Lewis acid promoted anomerisation

Lewis acid promoted anomerisation has potential in O- or S-glycoside synthesis. Herein, the anomerisation kinetics of thirty-one β-d-glucopyranosides was determined to determine how particular acyl protecting groups and their location influence reactivity towards a Lewis acid promoted reaction. The replacement of acetyl groups with benzoyl groups led to reduced reactivity when located at O-3, O-4 and O-6. However a reactivity increase was observed when the acetyl group was replaced by a benzoyl group at O-2. The 2,3,4,6-tetra-O-(4-methoxy)benzoate had an?～2-fold increase in rate when compared to the tetrabenzoate.     

Solvent and kinetic penultimate unit effects in the copolymerization of acrylonitrile with itaconic acid

Copolymerization of acrylonitrile (AN) with itaconic acid (IA) in dimethylformamide (DMF) and DMF/water mixture was investigated at enhanced concentrations of the latter. Analysis of the copolymer composition revealed the existence of a marked penultimate unit effect with respect to radicals terminated in AN. The reactivity of IA was considerably less than that of AN, manifested as a negative reactivity ratio for the former. The r_IA values ranging from −0.28 to −0.50 and r_AN values ranging from 0.53 to 0.70, were obtained by Kelen-Tudo's (KT) and extended KT methods. The penultimate reactivity ratios were determined by both linear and non-linear methods. The values ranged from r₁=0.009 to 0.01, r₁^′=0.0015 to 0.0043, r₂=0.54 to 0.69 and r₂^′=0.9 to 1.03. The reactivity of AN radical towards IA decreased about twofold when the latter formed the penultimate group. The penultimate model explained an acceptable rational feed-copolymer composition profile for the whole composition range. Addition of water decreased the reactivity of IA slightly. IA caused a decrease in the apparent copolymerization rate in agreement with the observed trends in the reactivity ratios; presence of water caused a further decrease in the rate of polymerization. A statistical prediction of monomer sequences based on reactivity ratios implied that IA existed as a lone monomer unit between the long sequences of AN units.     

Reactivity of allenoates toward aziridines: [3+2] and formal [3+2] cycloadditions

The reactivity of buta-2,3-dienoates toward aziridines is reported. Allenoates react as 2π-component in the [3+2] cycloaddition with the azomethine ylide generated from cis-1-benzyl-2-benzoyl-3-phenylaziridine affording 4-methylenepyrrolidines in a site-, regio-, and stereoselective fashion. Under conventional thermolysis, cis- and trans-2-benzoyl-1-cyclohexyl-3-phenylaziridines showed a different reactivity. These aziridines participate in formal [3+2] cycloadditions with allenes via C-N bond cleavage of the three-membered ring leading to functionalized pyrroles.     

Chiral relay in NHC-mediated asymmetric β-lactam synthesis II; asymmetry from NHCs derived from acyclic 1,2-diamines

The synthesis of a range of imidazolinium salts derived from acyclic 1,2-diamines, and an evaluation of the reactivity and asymmetric induction of the corresponding NHCs as catalysts for the asymmetric synthesis of β-lactams, is reported. An N-methyl-substituted NHC derived from (1R,2R)-1,2-diphenylethanediamine shows optimal reactivity and enantioselectivity in this series, in contrast to that observed with NHCs derived from (1R,2R)-cyclohexane-1,2-diamine.     

Formation et réactivité de carbanions α phosphoramides. Mise en évidence d'une nouvelle réaction d'élimination

The reactivity of (diethoxy)-N-methyl-N-benzyl phosphoramide (I) and bis(dinethylamino)-N-methyl-N-benzylphosphoramide (II) when treated with strong bases (RLi, R₂NLi) is very different: (I) gives a novel elimination, whereas (II) under the same experimental conditions gives a stable carbanion whose reactivity has been investigated.     

A method for determining reactivity ratios whenn copolymerizations are influenced by penultimate group effects

A novel kinetic treatment is proposed for the copolymerization of two monomers M₁ and M₂ when terminal −M₂· groups are susceptible to penultimate group effects. If [M₁] ⪢ [M₂], as is possible experimentally when M₂ is radioactively labelled, a value of the reactivity ratio r₁ which is independent of penultimate group effects can be obtained. This value is then used to find values for the other reactivity ratios. The method involves a solution for reactivity ratios by means of intersecting curves, each curve representing a given monomer feed ratio and copolymer composition ratio.     

An efficient catalytic system for the hydrogenation of quinolines

A new catalytic system ([Ru(p-cymene)Cl₂]₂/I₂) has been developed for the hydrogenation of quinoline derivatives with high reactivity. For the 2-methyl-quinoline, the hydrogenation reaction can proceed smoothly at an S/C of 20,000/1 with complete conversion. The iodine additive is important for the reactivity.     

Copolymerizations of 2-hydroxyethyl methacrylate with alkyl methacrylates

Copolymerizations of 2-hydroxyethyl methacrylate with ethyl methacrylate and n-butyl methacrylate were studied in bulk at temperatures between 60 and 80° using benzoyl peroxide as initiator. The monomer reactivity ratios were calculated using Joshi-Joshi, Fineman-Ross and intersection methods. The temperature had only a marginal effect on the reactivity ratios.     

Reactivity of allenoates towards aziridines: synthesis of functionalized methylenepyrrolidines and pyrroles

The reactivity of buta-2,3-dienoates towards aziridines is reported. Typically, allenoates react as the 2π-component in the [3+2] cycloaddition with azomethine ylides generated from aziridines, affording 4-methylenepyrrolidines in a site-, regio- and stereoselective fashion. However, N-cyclohexyl- or N-tert-butyl-2-benzoyl-3-phenylaziridines showed a different reactivity in the reaction with buta-2,3-dienoates. Pyrrole derivatives were obtained as single or major products resulting from a formal [3+2] cycloaddition via C-N bond cleavage of the three-membered ring heterocycle leading to functionalized pyrroles. From the reaction with allenoates bearing bulkier C-4 substituents 4-methylenepyrrolidines were also formed as minor products.     

Achieving flexible large-scale reactivity tuning by controlling the phase,thickness and support of two-dimensional ZnO

Tuning surface reactivity of catalysts is an effective strategy to enhance catalytic activity towards a chemical reaction. Traditional reactivity tuning usually relies on a change of the catalyst composition, especially when large-scale tuning is desired. Here, based on density functional theory calculations, we provide a strategy for flexible large-scale tuning of surface reactivity, i.e. from a few tenths of electronvolts (eV) to multiple eV, merely through manipulating the phase, thickness, and support of two-dimensional (2D) ZnO films. 2D ZnO films have three typical phases, i.e. graphene, wurtzite, and body-centered-tetragonal structures, whose intrinsic stability strongly depends on the thickness and/or the chemical nature of the support. We show that the adsorption energy of hydrogen differs by up to 3 eV on these three phases. For the same phase, varying the film thickness and/or support can lead to a few tenths of eV to 2 eV tuning of surface reactivity. We further demonstrate that flexible large-scale tuning of surface reactivity has a profound impact on the reaction kinetics, including breaking the Brønsted–Evans–Polanyi relationship.

Flexible large-scale reactivity tuning is achieved by manipulating the phase, thickness and support of two-dimensional ZnO, and a broken scaling relationship between adsorption and barrier is found via phase and termination engineering.     

Sterically Facilitated Intramolecular Nucleophilic NMe2 Group Substitution in the Synthesis of Fused Isoxazoles: Theoretical Study

The influence of steric repulsion between the NMe₂ group and a second ortho-(peri-)substituent in the series of 1-dimethylaminonaphthalene and N,N-dimethylanilene ortho-oximes on the ease of the NMe₂ group’s intramolecular nucleophilic substitution is studied. Possible reaction intermediates for three mechanisms are calculated (ωB97xd/def-2-TZVP), and their free Gibbs energies are compared to model reaction profiles. Supporting experiments have proved the absence of studied reactivity in the case of simple 2-dimethylaminobenzaldoxime, which allowed us to establish reactivity limits. The significant facilitation of NMe₂ group displacement in the presence of bulky substituents is demonstrated. The possibility of fused isoxazoles synthesis via the intramolecular nucleophilic substitution of a protonated NMe₂ group in the aniline and naphthalene series is predicted.     

N,N′-Di-Boc-2H-Isoindole-2-carboxamidine—First Guanidine-Substituted Isoindole

Synthesis of N,N′-Di-Boc-2H-isoindole-2-carboxamidine, the first representative of isoindoles containing guanidine functionality, was carried out. The cycloaddition reactivity of this new Diels–Alder heterodiene was studied and the title compound was employed as a cycloaddition delivery reagent for guanidine functionality. Higher reactivity was found in comparison with the corresponding pyrrole derivative. Substitution with fluorine or guanidine functionality does not change the reactivities of isoindoles, and these findings are in good accord with computational results.     

Small ring compounds—XXX : Homolytical aromatic substitution and hydrogen abstraction reaction with cyclopropyl radical

Homolytic aromatic substitution and hydrogen abstraction reactions with cyclopropyl radical were carried out to determine the reactivity and ionic character of cyclopropyl radical by examination of the orientation effect, partial rate factor and influence of substituents. By thermal decomposition of biscyclopropaneformyl peroxide in a series of substituted benzenes, the corresponding cyclopropylated benzene derivatives (the mixture of ortho, meta and para isomers) were obtained in moderate yield. In view of the orientation effect and the partial rate factor, the cyclopropyl radical seems to be fairly free from polar effect, and to resemble the phenyl radical more than the common alkyl radical although the cyclopropyl radical has a slightly higher reactivity than the phenyl radical. The relative reactivity of the 2-phenylcyclopropyl radical in the hydrogen abstraction reaction toward the benzylic position of ring-substituted toluenes gave good Hammett's correlation with the slope of + 0·20 suggesting little ionic character in the transition state. This result was in good agreement with the conclusion obtained from homolytic aromatic substitution reaction and with the chemical reactivity to be expected from the non-planar nearly sp²-hybridized conformation of the cyclopropyl radical.     

2-Thienylchlorocarbene: reactivity toward alkenes

Absolute rate constants for the additions of syn- and anti-2-thienylchlorocarbenes to various alkenes have been measured. The reactivity, selectivity, and structures of these species were characterized experimentally and computationally.     

A simple method of determining copolymerization reactivity ratios by means of a computer

A Fortran IV program for determining copolymerization reactivity ratios is proposed. The program is based on the curve-fitting method and has the advantage of delivering values free of personal judgement. To check its validity the system benzylacrylate (BeA)/methylmethacrylate (MMA) was investigated. The reactivity ratios obtained from the Fineman-Ross plots (r₁ = 0 · 34 ± 10 per cent and r₂ = 1 · 7 ± 10 per cent) are in good agreement with values obtained by using the proposed method (r₁ = 0 · 36 and r₂ = 1 · 78).     

Liquid-phase oxidation of alkyl-substituted cyclohexylbenzenes

The reactivity of alkyl-substituted cyclohexylbenzenes in liquid-phase oxidation was estimated by the k ₂/?k ₆ value which considerably decreased as the number of methyl groups in the substrate molecule increased. The observed difference in the reactivity of the title compounds was attributed to the degree of coplanarity of intermediate radical species.