V. I. Galkin

A new approach to the theoretical estimation of inductive constants

A new model of the inductive effect is proposed, allowing highly accurate theoretical calculations of inductive constants for a diversity of substituents, using a simple and readily available system of mathematics. According to this approach, the inductive effect of a substituent is considered in terms of the additive influence of its constituent atoms. A constant inherent capacity for inductive interaction with a reactive center (with a four-coordinate carbon atom chosen for such a center), represented by an atomic constant σA, is ascribed to each atom. Values of σA for a wide variety of atoms are determined, and their physical meaning is revealed to elucidate to a certain extent the physical nature of the inductive effect. In addition, the proposed model permits the convenient use in calculations of group constants σG characterizing the inductive power of groups. Values of σG are determined for molecular fragments that are most widely dealt with in organic chemistry, and the use of σA or σG constants and of their superposition is shown to have, in most cases, little or no effect on the accuracy and reproducibility of the results obtained. It is also shown that, in terms of the developed approach, the inductive effect of a substituent is closely associated with its conformation. Theoretical inductive constants were calculated for 427 organic, aromatic, organometallic and charged substituents, and they showed perfect correlation with the corresponding experimental values.

A novel approach to the analysis of substituent effects: quantitative description of ionization energies and gas basicity of amines

In this work, a new topological approach based on simple matrix algebra is introduced to explore substituent effects at the level of atomic additivity in the absence of significant resonance contributions. In the framework of the suggested method, all atoms are classified according to element and valence state. The sums of the inverse squared distances between the substituent atoms and the reaction centre of the molecule are used as operational parameters in the present method. The approach implies atomic level of consideration of inductive and steric effects and allows for quantification of substituent effects without the use of pre-established group substituent constants. The practical application of the model is illustrated by the quantitative interpretation of ionization energies and gas basicity of a broad range of amines. Further development of the elaborated approach is also discussed.

Kinetics and mechanism of triphenylphosphine quarternization with unsaturated carboxylic acids in the medium of acetic acid

Kinetics of reaction of triphenylphosphine with a series of unsaturated carboxylic acids and related esters in the medium of acetic acid as well as in mixtures of acetic acid and acetonitrile was studied by spectrophotometry. The data obtained show that the process of quarternization should be described by kinetic equation of third order, the proton transfer occurs from the solvent. A stepwise mechanism of interaction including formation of prereaction complex on the reaction pathway is proposed.

Kinetics and mechanism of quaternization of tertiary phosphines with unsaturated carboxylic acids. Kinetic studies of the reactions in aprotic solvents

Data obtained while studying the kinetics of quaternization of tertiary phosphines with the unsaturated carboxylic acids in the series of aprotic solvents indicate the participation of a second molecule of acid playing the part of the external proton donor in this process. Quantitative analysis of the effect of solvent within the frames of the Koppel-Palm equation showed that the main contribution in the reaction rate belongs to the nucleophilicity of medium while the effects of polarity and electrophilicity are smaller. The results obtained suggest the step-by-step mechanism of interaction including the formation of the zwitterionic intermediate on the reaction pathway common for the solvents with different proton activity.

Kinetic study of the reaction of triphenylphosphine with acrylic acid in alcohol media

Kinetic study of the reaction of triphenylphosphine with acrylic acid in alcohol media was carried out by spectrophotometric method. Use of alcohols as solvents is shown to introduce a specific feature in the kinetic picture of the reaction due to the appearance of parallel channels of proton transfer: from alcohol and from another molecule of acrylic acid in the solution.

Synthesis and Properties of Phosphabetaine Structures: III. Phosphabetaines Derived from Tertiary Phosphines and α,β-Unsaturated Carboxylic Acids. Synthesis, Structure, and Chemical Properties

Methods of synthesis of acylate phosphabetaines by reactions of triphenylphosphine with methacrylic, cinnamic, and p-methoxycinnamic acids are developed. The phosphabetaine form is proposed to exist in equilibrium with the σ5-oxaphospholane form. The features of methylation of the phosphabetaines are discussed.

Kinetics and Mechanism of Triphenylphosphine Quarternization with Unsaturated Carboxylic Acids in Various Media

Abstract Reactions of tertiary phosphines with unsaturated electrophilic reagents are widely used in synthetic organic chemistry. Typical satellites of these transformations are proton migration processes, which can play decisive role in such reactions. To learn more about proton transfer mechanism, kinetics of reaction of triphenylphosphine with a series of unsaturated carboxylic acids in alcohols, carboxylic acids, and aprotic solvents was studied by spectrophotometry. The form of kinetic equation depends on proton–donor properties of solvent and has a general third order. Proton transfer occurs from the solvent in carboxylic acids; the second molecule of substrate is required in aprotic solvents, and both canals of proton migration take place in alcohols. Existent proton transfer canals are isokinetic, attesting to the invariability of general features of the reaction mechanism independent of proton–donor nature at the last step of the interaction. A stepwise mechanism including initial generation of 1,3-dipole followed by proton transfer to the carbanionic centre from the medium is suggested.

An Unusual Reaction of Triphenylphosphine with Dichlorodinitrobenzofuroxan

A novel phosphorylation reaction of dichlorodinitrobenzofuroxan by triphenylphosphine has been studied. An unusual course of the reaction with the participation of benzofuroxan nitro groups as reactive centers has been established. It is shown that as final product of the reaction, a stable diphenolate diphosphabetaine with strong participation of the mesomeric ketoylide structure is formed. The structure of the product has been confirmed by X-ray diffraction.

Synthesis and Properties of Phosphabetaine Structures: II. Synthesis and Molecular Structure of 3-(Triphenylphosphonio)propanoate and Its Alkylation Products

The structure of 3-(triphenylphosphonio)propanoate was studied, and the ability of proton-donor reagents to stabilize the betaine structure was demonstrated. The phosphobetaines are alkylated by alkyl halides to form (alkoxycarbonyl)alkyltriphenylphosphonium halides and acylated by acetyl bromides. Some features of the latter reactions were revealed.

“Inductive” electronegativity scale

Abstract A new approach to the calculation of group electronegativity is introduced on the basis of previously elaborated additive models for steric and inductive effects. The newly derived “inductive” group-electronegativities χ I correlate well with other well-established electronegativity χ scales. A firm interrelation between three fundamental substituent characteristics: inductive and steric constants and group electronegativity is suggested.