A new theoretical approach to the empirical resonance energies of the aromatic hydrocarbons

In the framework of the Hückel MO approximation, the differences in total binding energy between a given molecule and the corresponding distorted Kekulé-type structure are calculated for a variety of benzenoid hydrocarbons. The total binding energy is assumed to be given by the sum of the w88j6287438g48/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-electron and w88j6287438g48/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">-electron binding energies. It is shown that there is a good linear relationship between the calculated differences in total binding energy and the w88j6287438g48/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-electron delocalization energies (DE) as obtained by using the simple Hückel MO method. This provides a physical basis for the use of the w88j6287438g48/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-electron DE as a theoretical index to the empirical resonance energy (RE). Further, by examining the changes in w88j6287438g48/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-electron binding energy between a given molecule and the corresponding distorted Kekulé-type structure, it is concluded that in benzenoid hydrocarbons the main contributor to the RE is not the w88j6287438g48/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-electron DE but the compressional energy of w88j6287438g48/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0"> bonds.     

Terpenes in organic synthesis

A seven-step synthesis ofS-(+)-hydroprene (S-1) in w037843t2/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">20 % overall yield starting fromS-(+)-3,7-dimethyl-1,6-octadiene (2) of 55+-10 % optical purity is described. The introduction of an optical enhancement step in the synthetic sequence at the stage ofS-(–)-3,7-dimethyl-1-octanol (9) raises the optical purity ofS-1 from w037843t2/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">50 % to w037843t2/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">80 %.For part 13, see. ref.¹ Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 342–348, February, 1993.     

弱碱性阴离子交换树脂分离1,6—二磷酸果糖的研究

采用弱碱性阴离子交换树脂HJ-30对发酵液中1，6-二磷酸果糖的分离进行了研究。详细地研究了树脂的吸附和脱附性能。实验结果表明，HJ-30树脂对FDP的吸附量达0．28gFDP／g湿树脂，以0．05mol／LNaCl洗脱光机磷和1mol／LNaCl洗脱1，6-二磷酸果糖，产品的收率和纯度分别为92％和99．4％。     

Molecular structure of potassium [N,N′-bis(salicylideneamino)nitroguanidonate-N,N′,-O,O′]nickel(ii), the product of condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template

The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni²⁺ ion template, K[Ni(C₁₅H₁₀N₅O₄)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]^– anions and solvated [K⁺ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996.     

The preparation of thick-film glass capillary columns

A detailed method for the routine preparation of glass capillary columns is presented. The method consists of coating a glass tube with quartz powder prior to pulling the tube into a capillary. The inner surface of the capillary consists of an even distribution of quartz particles fused to the walls. This surface has been found readily deactivated by standard procedures and ideal for the preparation of thick-film glass capillary columns. The method has been thoroughly tested in two independent laboratories to ensure that the procedures described are reproducible.     

Studies of solvent effects

The effect of water on the conformational preferences of acetylcholine has been studied within the w2551t1r7775x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">discretew2551t1r7775x233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0">, the w2551t1r7775x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">continuumw2551t1r7775x233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> and the combined w2551t1r7775x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">discrete-continuumw2551t1r7775x233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio w2551t1r7775x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">super-moleculew2551t1r7775x233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> treatment. The continuum model utilized here represents a net improvement above such models utilized in other works.     

On the affinity of cytosine towards electrophiles

Ab initio SCF computations on the intrinsic preferences of the H⁺, CH ₃ ⁺ and C₂H ₅ ⁺ cations towards the two principal sites of protonation or alkylation on cytosine, N₃ or O₂, show that this preference undergoes a continuous modification with the increase in size and complexity of the cation. N₃ is the preferred site of fixation of H⁺, O₂ the preferred site of C₂H ₅ ⁺ , while CH ₃ ⁺ has no marked preference. The exchange repulsion term of the binding energy appears responsible for the preference of C₂H ₅ ⁺ for O₂.This work was supported by the Ligue Francaise contre le Cancer and the National Foundation for Cancer Research (USA)     

Kinetics and mechanism of reaction of cis-α,β-dinitrostilbene with morpholine

Reaction of cis-w5u2/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">,w5u2/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-dinitrostilbene (substrate) with morpholine (reagent) in n-hexane leads to cis-w5u2/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-nitro-w5u2/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-morpholinostilbene (end product). The process is of first order with respect to the substrate and second order with respect to the reagent. Possible reaction mechanisms are analyzed, and it is established that the following are most probable on the basis of kinetic patterns and stereochemistry: development of a charge transfer complex having a hydrogen bond between the substrate nitro group and reagent amino group; reaction of the complex with a second reagent molecule and formation of a carbanion (this stage determines the overall reaction rate); and detachment of a nitrite ion from the nitrocarbanion and its protonation to form the end product.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. A. N. Nesmeyanov Institute of Heteroorganic Compound, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 78–83, January, 1992.