Reactions of Azolium cations. II [1]. Regioselective N2 alkylation of 5-aryltetrazoles with isopropyl alcohol in sulfuric acid media: Effect of electronic properties of aryl substituents on the reaction rate

Kinetics of regioselective N2 alkylation of a series of 5-(R-phenyl)tetrazoles with isopropyl alcohol has been studied in 88.2, 94.3, and 98.3% (w/w) sulfuric acid at 25°. The true rate constants were evaluated, logarithms of which were found to correlate with σ° constants of phenyl substituents as log k = ?0.488 σ° ? 0.417. Small value of Hammett constant ρ is evidence of a considerable isolation of the reaction center from the influence of the substituent at position C5 of the heteroring. This conclusion is confirmed by results of MNDO quantum chemical calculations of a series of 5-substituted tetrazolium cations. A correlation between logarithms of the true rate constants and the calculated net effective charges on atoms N2(N3) for 5-(R-phenyl)tetrazolium cations has been revealed. © 1995 John Wiley & Sons, Inc.     

Branched polycyclic tetrazole systems. 1. Synthesis and structure of 2-(5-tetrazolyl)ethyl derivatives of some CH-, OH-, and NH-acids

The cycloaddition of dimethylammonium azide to the nitrile groups of 2-cyanoethyl derivatives of CH-, OH-, and NH-acids leads to open-chain branched structures containing terminal NH-tetrazolyl groups. An x-ray diffraction structural analysis of tris[2-(5-tetrazolyl)ethyl]nitromethane revealed steric access of the equivalent NH-tetrazolyl rings of the branched system. In going from the branched nitrile substrates to the corresponding tetrazoles, the PMR spectra show a breakdown in the resolution of the multiplet components, which had not been observed previously for monocyclic 5-substituted tetrazoles. A dependence was found for the¹³C NMR chemical shifts on the pK_a values, reflecting the NH-acidity of the branched polycyclic tetrazoles in water. Dedicated to the memory of I. N. Goncharova. St. Petersburg State Technological Institute, 198013 St. Petersburg. V. A. éngel'gart Institute of Molecular Biology, Russian Academy of Sciences, 117984 Moscow. L. Ya. Karpov Physics and Chemistry Research Institute, 103062 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1494–1501, November, 1997.     

The System Polyacrylamide—Water

The system polyacrylamide (PAA) — water at 0<n<25 (n=H₂O/(-C(O)NH₂)) was investigated. In air of 100% humidity at 292 K, at equilibrium n≈18. The differential heat of water vapour sorption decreases from 56 kJ mol¹ (initial heat) to the heat of water vaporization (Q _L) at n≈0.5, and then up to n=18 it passes through several maxima and minima in the vicinity of Q _L; at n>18, it is equal to Q _L. The mechanism of the gradual solution of PAA is proposed. As the system sorbs water, it passes through the consecutive stages of formation of the clathrate-like compounds AG·2H₂O and AG·(17?18)H₂O (AG is an amido group of PAA) with subsequent formation of a perfect aqueous solution of compound I.     

Structure distortion effects in the spectrum of tunnel-exchange states of tetrahedral mixed-valence tetramers

Tunnel-exchange states of a tetrameric mixed-valence (MV) d₁–d₁–d₁–d₂ cluster are considered. Energy levels of distorted pseudotetrahedral conjiprations with rhombic and trigonal symmetry are calculated. It is demonstrated that the correlation diagrams of planar systems are symmetric with respect to the sign of the double exchange parameter. A strong double exchange always results in the ferromagnetic ground state of planar systems. The following types of spectrum defamations of the d₁–d₁–d₁–d₂ tetramer from tetrahedral to planar systems have been found: a) with a weak positive double exchange, deformation of a tetrahedral system does not lead to any change of spin of the antiferromagnetic ground state of the cluster; b) with a strong positive double exchange, the defonnation alters the antiferromagnetic ground (S = 1/2) state of the tetrahedral system to the ferromagnetic (S = 5/2) state of the planar system, or to an intermediate (S = 3/2) state; c) with a negative double exchange, irrespective of its absolute value, the tetrahedral system deformation does not alter the spin of the ground state. With a weak double exchange, this ground state remains antiferromagnetic, and with a strong double exchange, it is ferromagnetic or intermediate.Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 33–46, September–October, 1993.Translated by L. Chernomorskaya     

Polynuclear Branched Tetrazole Systems. 2. New 2-(5-Tetrazolyl)ethylpodands and Their NH-Acidity

Nine new polynuclear 2-(5-tetrazolyl)ethyl podands have been obtained by the azidation of the corresponding nitriles. Using Bjerrum distribution functions, the values of pK _a ¹, pK _a ², pK _a ³, and pK _a ⁴ have been determined by a potentiometric method for 14 polynuclear tetrazoles in aqueous and aqueous methanolic solution. The found values lie in the range from 3.5 to 7.5 pH units. The overall rules and the sequence of the ionization of the spatially separated tetrazole fragments in these podand systems are discussed.     

A study of the acid-base transformations of oxodihydrothiochrome

The acid-base properties of oxodihydrothiochrome — the product of the redox disproportionation of the vitamin B₁ catabolite thiochrome (pH=10.7, 4.5, and 0.5) — have been studied in the pH interval of 0–12 by PMR spectroscopy. It has been established that in acid medium (pH 0–1) the formation of a doubly charged ion is accompanied by a further structural transformation of the molecule of (I) with the formation of a vitamin B₁ analogue — oxothiamine (II). A possible mechanism of the action of (I) as an inhibitor of thiamine-dependent enzymes is discussed in the light of the results obtained. Details of the PMR spectra of (I) and (II) are given.