Solvation effects on alternative nucleophilic substitution reaction paths for chloride/allyl chloride and gamma-methylated congeners

An adiabatic connection method, mPW1PW91(0.581)/6-31G(d), was employed in conjunction with the continuum solvation model SM5.42 to study the effects of solvation on the S(N)1, S(N)2, and syn and anti S(N)2' nucleophilic substitution reactions of chloride anion with allyl chloride and its gamma-methylated analogues Z- and E-crotyl chloride and isoprenyl chloride. The impact of equilibrium solvation on the potential energy surfaces of these systems is large and leads to significant changes in both the geometries and the relative energetics of different reaction pathways for different species. The predicted effects of increased solvent dielectric constant are consistent with available experimental data and provide semiquantitative insights into the relative influence of different solvents on particular properties.     

Acid-catalyzed acetylation of N-methallyl lactam and imide derivatives

The reactions of N-methallyl derivatives of cyclic amides and imides with acetic and propionic anhydride have been studied in the presence of perchloric acid. The reaction products have been found to be pyrylium and oxazolinium salts. The relationship between the reaction pathway and the structure of the imide or amide starting material has also been determined. Pyrylium salts have been converted to their corresponding pyridine bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1414–1419, October, 1988.     

Formation of 1,2-oxazine derivatives: A novel type of reaction between 2-aminooxazoles and maleic acid imide

N,N-Disubstituted 2-aminooxazoles in acetic acid at 20°C undergo addition of maleinimide, converting to alkylidene succinimides or 1,2-oxazine derivatives.N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913; e-mail: zhulin@cacr.ioc.ac.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1128–1131, August, 2000.     

A copper-catalyzed four-component reaction of arylcyclopropanes,nitriles, carboxylic acids and N-fluorobenzenesulfonimide: facile synthesis of imide derivatives

An unprecedented copper-catalyzed four-component reaction of arylcyclopropanes, nitriles, carboxylic acids and N-fluorobenzenesulfonimide (NFSI) has been successfully developed, which represents the first example of a four-component reaction of non-donor–acceptor cyclopropanes. A wide range of imide derivatives were efficiently synthesized in excellent yields under mild conditions.

An unprecedented copper-catalyzed four-component reaction of arylcyclopropanes, nitriles, carboxylic acids and N-fluorobenzenesulfonimide (NFSI) has been successfully developed, efficiently synthesizing diverse imide derivatives.     

Thermal decomposition of amide and imide derivatives of maleated polyethylene

The thermal decomposition behavior of six derivatives of maleated polyethylene was investigated by high‐resolution pyrolysis gas chromatography–mass spectrometry. The results revealed that substituents attached to maleated polyethylene as amides formed from secondary amines were significantly less stable than imides formed from primary amines. Morpholine amide and N‐methylaniline amide derivatives of maleated polyethylene underwent significant decomposition at 160 °C and substantial decomposition at 200 °C. In contrast, the imide derivatives of maleated polyethylene were stable for long periods of time at elevated temperatures. Following 2 min of heating, the first traces of decomposition were detected at 200 °C for the 2‐aminoanthrancene imide derivative, at 255 °C for the 2‐phenethylamine imide, and at 280 °C for the 9‐aminomethylphenanthrene imide. With the exception of the 9‐aminomethylphenanthrene imide, all other derivatives decomposed to form the corresponding amine as the single most significant volatile product. The most likely explanation for this result is that the polymer contained small amounts of succinamic acid that did not close to form the imide. We concluded that the imide was stable even to 315 °C and that the amine was lost from β‐carboxyamide groups present in the sample. In the 9‐aminomethylphenanthrene imide derivative, we observed no loss of amine. Instead, we observed an alternative fragmentation process yielding 9‐methyl phenanthrene. The dependence of the thermal stability of these various derivatives of maleated polyethylene has important implications for the design of reactive‐blending strategies for polyolefins with other functional polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 730–740, 2000     

Chemical reaction paths and calculus of variations

The reaction path is an important concept of theoretical chemistry. We analyze different forms of reaction pathways in the light of the abstract theory of calculus of variations such as steepest descent from saddle point, the intrinsic reaction coordinate (IRC), Newton trajectory, variationally optimized reaction paths and others. The paper is both a mathematical review and a pointer to future research. Besides the theoretical definitions, we shortly discuss hints at the numerical effect of the definitions.     

Tunneling reactions with two reaction paths

The WKB method and Taylor series expansions are used to derive an approximate expression relating the tunneling rates with two reaction paths to the tunneling rates of the individual paths. The two reaction paths originate in the same reactant well, travel over different potential barriers, and finish in the same product well. The validity of the approximate expression and the applicability of the WKB method to this problem are investigated.     

Solvation effects in the methylation of barbituric acid and its derivatives by diazomethane

Methylation of barbituric acid and its N-methylderivatives by diazomethane in ethers and methanol occurs only at the oxygen atom of the -dicarbonyl fragment. The resulting 6-methoxy-2,4-dioxo-1,2,3,4-tetrahydropyrimidine and its derivatives are methylated at both the oxygen and nitrogen atoms; relative to ethers, methanol facilitates a greater degree of methylation at the nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1523–1526, November, 1987.     

Survival paths for reaction dynamics in fluctuating environments

We study rate processes in general Gaussian fluctuating environments using a path integral formalism. We derive a variational equation for the dominant survival path when the fluctuations relax exponentially or according to a stretched exponential law. In the case of a slowly varying barrier, the equilibrium regression approximation which is used by Frauenfelder and coworkers emerges. In this approximation, the survival path follows the ordinary law of relaxation to equilibrium. If the rate coefficients vary rapidly with environmental variables, however, the dominant survival paths exhibit more complex behaviour. Many phenomena analogous to geometrical optics occur. These include reflection off of rapid variations in rate constant, as well as refraction, giving paths very different from the equilibrium relaxation properties. A model with a piece-wise linear rate exhibits the basic phenomena, and the survival path equation is exactly solved for the general stretched exponential relaxing environment.     

MINDO-Forces calculation of molecular geometries and reaction paths

A new method for the minimization of molecular energies is described, based on the Murtagh-Sargent procedure and the MINDO/2(3) semiempirical MO method. The derivative of energy is calculated according to the Pulay's Force method. This method was applied to the calculation of heats of formation and geometries of different organic molecules. The results agree well with the experimental and theoretical values known in the literature. The MINDO-Forces method was applied to the calculation of the internal rotation barrier of the benzyl carbonium ion. The calculated value 18.79 kcal/mol agrees well with the theoretical values known in the literature. The MINDO-Forces method was applied to the calculation of the internal rotation barrier of cyclopropyl carbinyl cation. The calculated rotation barrier, 21.28 kcal/mol is in agreement with the known theoretical values and with the expectation based on the NMR measurement of the barrier height in cyclopropyl dimethyl-carbinyl cation. Part of the Ph.D. thesis, S. M. Khalil, University of Baghdad 1976.     

A novel three-component reaction of allenoates, isocyanides, and carboxylic acids: facile synthesis of highly substituted acryl imide derivatives

A novel synthesis of highly substituted acryl imide derivatives by the three-component reaction of allenoates, isocyanides, and carboxylic acids was reported, and the intramolecular cyclization reaction of allenoic acids with isocyanides was also described.     

Intrinsic reaction coordinate calculations for reaction paths possessing branching points

A 3-21+G energy surface corresponding to the proton transfer reaction in the hydroperoxyl anion solvated by one water molecule presents interesting topological features. In particular the intrinsic reaction coordinate that begins at the transition state does not lead to a minimum but to a saddle point of second order passing through two branching points. A new strategy to obtain the true reaction path in these cases is proposed.     

Finding reaction paths using the potential energy as reaction coordinate

The intrinsic reaction coordinate curve (IRC), normally proposed as a representation of a reaction path, is parametrized as a function of the potential energy rather than the arc-length. This change in the parametrization of the curve implies that the values of the energy of the potential energy surface points, where the IRC curve is located, play the role of reaction coordinate. We use Caratheodory's relation to derive in a rigorous manner the proposed parametrization of the IRC path. Since this Caratheodory's relation is the basis of the theory of calculus of variations, then this fact permits to reformulate the IRC model from this mathematical theory. In this mathematical theory, the character of the variational solution (either maximum or minimum) is given through the Weierstrass E-function. As proposed by Crehuet and Bofill [J. Chem. Phys. 122, 234105 (2005)], we use the minimization of the Weierstrass E-function, as a function of the potential energy, to locate an IRC path between two minima from an arbitrary curve on the potential energy surface, and then join these two minima. We also prove, from the analysis of the Weierstrass E-function, the mathematical bases for the algorithms proposed to locate the IRC path. The proposed algorithm is applied to a set of examples. Finally, the algorithm is used to locate a discontinuous, or broken, IRC path, namely, when the path connects two first order saddle points through a valley-ridged inflection point.     

Coordinate reduction for exploring chemical reaction paths

The potential energy surface for the reaction of a typical molecular system composed of N atoms is defined uniquely by 3N-6 coordinates. These coordinates can be defined by the Cartesian coordinates of the atomic centers (minus overall translation and rotation), or a set of internally defined coordinates such as bond stretches, angle bends, and torsions. By applying principal component analysis to the geometries along a reaction path, a reduced set of coordinates, d ≪ 3N-6, can be obtained. This reduced set of coordinates can reproduce the changes in geometry along the reaction path with chemical accuracy and may help improve the efficiency of reaction path optimization algorithms.     

Stereochemistry of reaction paths at carbonyl centres

Results of recent experimental and theoretical studies of nucleophilic addition to carbonyl groups are described. The reaction paths found by different methods for different nucleophiles show some striking similarities that appear to be characteristic for the reaction type.     

Hafnium (IV) bis(perfluorooctanesulfonyl)imide complex catalyzed synthesis of polyhydroquinoline derivatives via unsymmetrical Hantzsch reaction in fluorous medium

A facile and efficient synthesis of polyhydroquinoline derivatives was reported via four-component condensation reaction of aldehydes, dimedone, active methylene compounds, and ammonium acetate in the presence of Hf(NPf₂)₄ in C₁₀F₁₈ at 60 °C. The method offers several advantages including high yields, short reaction time, simple work-up procedure and catalyst reusability.