Tibor Sticzay

Optical rotary dispersion studies. Correlation between the structure and o.r.d. curves of acyclic ketoses

Abstract The o.r.d. curves of some tetruloses and 2- and 3-pentuloses have been measured and a relation has been found between the structure of the ketoses and their Cotton effects.

Base-catalyzed β-elimination of 2,3-di-O-methyl-d-glyceraldehyde

Abstract 2,3-Di- O -methyl- d -glyceraldehyde undergoes base-catalyzed β-elimination with formation of 2-methoxypropenal in two steps by the ElcB mechanism. The first step is a rapid, reversible, general base-catalyzed reaction giving an anionic intermediate of 2,3-di- O -methyl- d -glyceraldehyde. The second, slower step involves liberation of methoxide ion from the intermediate to give 2-methoxypropenal as the end-product. Reversibility of the first step was proved by incorporation of deuterium at C-2 of the starting compound. The order of the reaction decreases with increasing concentration of catalyst. A kinetic equation reflecting this fact was derived to determine the equilibrium constant of the first, reversible step and the rate constant of the second step. The mechanism of the reaction was elucidated on the basis of the kinetic rate-constants, deuterium solvent isotope-effect, and the activation parameters.

O.R.D. characteristics of azido derivatives of pentoses

Abstract O.r.d. curves of some methyl 4-azido-4-deoxypentopyranosides have been measured. Although it is not possible to predict, on the basis of analysis by an azide octant rule, the sign of the Cotton effect exhibited by these derivatives, several empirical observations are noteworthy. Those derivatives in the C1 ( d ) conformation and having an axial azide substituent exhibit positive Cotton effects, whereas those having an equatorial azide substituent show negative Cotton effects. Azide derivatives in the 1C ( d ) conformation and having an equatorial azide group exhibit a negative Cotton effect, whereas those having an axial azide substituent show a positive Cotton effect. There is a marked dependence of the magnitude of the background rotation on the configuration of the substituent at C-1; an axial, glycosidic, methoxyl group causes a much higher background rotation than does an equatorial substituent.