Selective modification of the 2-position of pyridoxol

Pyridoxol, protected by acetylation of the hydroxyl groups, has been converted to its N-oxide which upon reaction with perfluoroacetie anhydride yields a 2-nor-2-hydroxymethylpyridoxol derivative as an intermediate. This compound undergoes acyl migration from the 3-position. Protection of the pyridoxol hydroxyls by benzylalion followed by the same treatment yields the unrearranged α²-hydroxy derivative. This compound has been converted to a series of α²-substituted pyridoxols (X = -Cl, -Br, -OCOCH₃, -OCH₃, -OC₂H₅).     

Equivalence and conservation rules for the total integral cross section in molecular collisions

The rule of conservation of the total integral cross section o_Tj) is described in a general way using the opacity function. An equivalence rule which states that at the same initial kinetic energy, the total integral cross section from the initial state j is equal to that from the initial state j, i.e., o_Tj) is also presented. Both rules are demonstrated with numerical examples in the He + H₂ collision system and counter-examples are also presented. Possible uses of the rules in the inversion of the intermolecular surface and as an experimental tool are also discussed.     

Regioselective hydroborations of methylvinylchlorosilanes

The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl_nMe_3?nSiCHCH₂ (n= 0 ? 3), has been investigated using BH₃←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols forn= 0 and 1. Forn= 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol-0-d provides a more effective means of derivatization. Addition of the alkenes,n= 2 or 3, to excess BH₃←THF givesca. 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes giveca. 80% of the β-boron adducts.     

Benzothiazolium derivatives. III. Nucleophilic substitution reactions of benzothiazolium salts

The reactions of 2,3-dihydrothiazolo[2,3-b]benzothiazolium bromide 1 (A^? ?Br^?) with certain nucleophilic reagents have been performed for the purpose of ascertaining the reaction pathways and identifying the group that is displaced from the central carbon atom of the dithiocarbamate system. The nature of complex salt-like intermediates formed initially from 1 (A^? ?Br^?) has been studied and confirmed. For comparison, a number of nucleophilic substitution reactions of 2-methylthio-3-methylbenzothiazolium iodide 17 and 2-dimethylamino-3-methylbenzothiazolium perchlorate 18 have been examined.     

NMR studies of bond orders in heteroaromatic systems

Fifty-seven values for the ortho-benzylic coupling constant ⁴J_{Me? C?C? H} (henceforth denoted as ⁴J_OB) were obtained for a variety of heteroaromatic systems. It was shown that a good correlation exists between ⁴J_OB when the methyl group is not α to the heteroatom and the SCF-MO bond order. This method can therefore be used as an experimental means of determining bond orders in heteroaromatic systems. An examination of bond alternation in thirteen heteroaromatic systems has given a measure of relative “degree of aromaticity” for a larger number of systems than previously reported by any single method.     

Discrete lattice systems and the equivalence of microcanonical,canonical and grand canonical Gibbs states

It is proven that a microcanonical Gibbs measure on a classical discrete lattice system is a mixture of canonical Gibbs measures, provided the potential is approximately periodic, has finite range and possesses a commensurability property. No periodicity is imposed on the measure. When the potential is not approximately periodic or does not have the commensurability property, the inclusion does not hold.As a by-product, a new proof is given of the fact that for a large class of potentials, a canonical Gibbs measure is a mixture of grand canonical measures. Thus the equivalence of ensembles is obtained in the sense of identical correlation functions.