Field desorption mass spectra of stereoisomeric glycosides

Field desorption mass spectrometry (FD-MS) yields differentiated spectra for unshielded α- and β-stereoisomeric glycosides. The small but characteristic differences enable a distinction to be made between the two isomers. Valuable structural information can be deduced from the simple cleavage between the sugar moiety of the molecule and the aglycon. A short comparison with electron-impact (EI) and field ionisation (FI) spectra is given.     

Hydrolysis of amides. Steric effects on kinetics and mechanism of the basic hydrolysis of N-acylcarbazoles

The hydroxide ion catalyzed hydrolysis of a series of N-acylcarbazoles has been studied in water at 25°. Both the rate constants of formation of the tetrahedral intermediate and of its collapse to products are strongly increased by alkyl group branching in the acyl portion.     

The alkaline hydrolysis of flavonoid glycosides

Conclusions 1. The alkaline hydrolysis of flavonoid glycosides has been studied.2. In an alkaline medium 3-glycosides, C-glycosides, and biosides having 1, 2 bonds between the sugars are stable.3. The difference in the stabilities of the glycosides to alkalis can be used in studying flavonoid O-diglycosides, O-biosides with different positions of the bond, O,C-diglycosides, and O,C-biosides.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 5, pp. 366–369, 1969     

Kinetics of the alkaline hydrolysis of flavonoid glycosides

Summary 1. In a study of the kinetics of the alkaline hydrolysis of flavone glycosides it has been found that derivatives of 3,3,4,5,7-pentahydroxyflavone hydrolyze faster than derivatives of 3,4,5,7-tetrahydroxyflavone and of 3,4,5,7-tetrahydroxy-3-methoxyflavone.2. In the hydrolysis of diglycosides of 3,3,4,5,7-pentahydroxyflavones the maximum amount of intermediate product is formed after 2 min (3,4,5,7-tetrahydroxyflavone glycoside), and in the case of 3,4,5,7-tetrahydroxy-3-methoxyflavone glycosides after 120–150 min.I. V. Kutateladze Institute of Pharmacochemistry, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 646–649, September–October, 1977.     

Steric substituent effect on the resin catalyzed hydrolysis of alkyl acetate esters

The rates of hydrolysis of seven acetate esters substituted in the alkyl group have been studied in the presence of a sulfonated cation exchange resin in 70% aqueous acetone solution. the slower hydrolysis rates with increasing size of substituent are related to increasing steric influence, as determined by decreasing values of the steric substituent parameter, E_s. The efficiency of the resin catalyst is related to the entropy of substituents. Influence caused by steric hindrance on reaction rates accounts satisfactorily for observed variations of the enthalpies and entropies of activation with alkyl group substituents. The entropy, S^x, values increase in the order: n-octyl-

, , 70%- . , , E_S. . , . , S^*, : --<-<, .

     

Steric effects in the hypervalent iodine oxidation of ketones

Oxidation of 3-cholestanone (1) with C₆H₅I(OAc)₂ or o-OIC₆H₄COOH or C₆H₅IO₂ in KOH/MeOH yields 2 α-carbomethoxy-A-norcholestane (2). This result is interpreted on mechanistic grounds and compared with the course of the reaction with other sterically hindered ketones such as friedelin, 3-keto, 12-keto, 17-keto steroids, and 2,2,6,6-tetramethyl-4-piperidone.     

Steric effect of substituents in haloarenes on the rate of cross-coupling reactions

The relative reactivity of ortho- and para-methyl-substituted iodoarenes in the Sonogashira reaction and palladium-catalyzed methoxycarbonylation, as well as of similarly substituted bromoarenes in the Suzuki reactions and cobalt-catalyzed methoxycarbonylation, was studied. Introduction of a methyl group into the para position of aryl halide slows down the cross-coupling. o-Methylhaloarenes are less reactive in palladiumcatalyzed reactions as compared to both unsubstituted haloarene and para-substituted analog. The presence of a methyl group in the ortho position with respect to the reaction center accelerates cobalt-catalyzed methoxycarbonylation.     

Steric effects in mono- and polynitroalkane molecules

Conclusions The equilibrium configurations, strain energies, and atomization enthalpies were calculated for a number of mono- and polynitroalkane molecules. A steric hindrance criterion was derived, which could be one of the parameters that characterize the stability. The steric effects, caused by nitro groups, increase in a nonlinear manner with increase in the number of nitro groups in the molecule and elongation of the carbon skeleton.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 182–184, January, 1977.     

Steric effects control self-sorting in self-assembled clusters

Endohedrally functionalized bis(pyridine) ligands show the ability to self-discriminate when treated with coordinating metals to form self-assembled clusters. Self-sorting between components is controlled by substitution on the interior of the complex. Tuning the size of the internal substituent allows selective heterocluster formation, determined by noncovalent and space-filling interactions. This novel method of self-sorting allows discrimination between ligands of identical geometry and donor type.     

Steric effects in the recyclization of nitropyridinium salts to nitroanilines

The effect of the degree of branching of alkyl groups attached to the amine nitrogen atom on the recyclization of 1,2,4,6-tetramethyl-3-nitropyridinium iodide to nitroanilines was studied.Decreased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1268–1271, September, 1980.     

Steric effects in the synthesis of pyrroloindoles from 5-aminoindols

The formation of angular pyrroindoles from 5-aminoindole substitued in the pyrrole ring depends both on the steric requirements of the substituent at the-position of the pyrrole ring, and on the structure of the -hydroxyketone. Significant amounts of the angular pyrroloindole are only formed together with the linear pyrroindole in the reaction of 2-methyl-5-aminoindole with benzoin. In the remaining cases, the linear ring closure of the pyrrole ring predominates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 55–57, January, 1995.     

Steric effects in the enantioselective transfer hydrogenation of 2-aroylacetates

Benzoylacetate esters and aryl-substituted derivatives are efficiently reduced in 2-propanol using the readily available catalytic combination (1S,2R)-ephedrine/[RuCl₂(η⁶-p-cymene)]₂ to give the corresponding alcohols in high yields and enantioselectivities (up to 94% ee).