Publisher Summary This chapter discusses the use of boric acid for the determination of the configuration of carbohydrates. For the polyhydroxy compounds, the conductivity in water and subsequently in 0.5 M boric acid at 25°C is determined. Aliphatic, noncyclic glycols without adjacent hydroxyl groups have no effect, and they cannot form cyclic complexes. With an increase in number of adjacent groups, two hydroxyl groups are more favorably situated with reference to one another, as is unmistakably shown by the following results of determinations. The α-hydroxy acids cause a very considerable increase in the conductivity of boric acid; this may be explained by assuming that the carboxyl group is hydrated to C(OH)*, as a result of which a very favorable situation prevails in these acids for the formation of a boric acid complex.

The use of Boric Acid for the Determination of the Configuration of Carbohydrates

Haslam’s previous accounts of this area of flavonoid chemistry (Haslam, 1975, 1982a) eloquently summarized the historical developments in the chemistry and biochemistry of this important and complex group of plant phenolics. Also covered were their relationship with condensed tannins and aspects of their characteristic chemical and spectroscopic properties and metabolism.

Flavans and proanthocyanidins

Publisher Summary The relative configuration assigned to naturally occurring amino acids is obtained mainly from the parallelism of changes in molecular rotations observed with ionization and substitutions in similarly constituted derivatives of amino and hydroxyl acids, respectively. This chapter describes the validity of such deductions. It also describes racemization and occurrence of D-amino acids and their derivatives in nature. Many amino acids having specific rotations differ in both magnitude and sign and can be transformed into each other by chemical reactions that do not involve asymmetric carbon atom. Any molecule lacking a plane or center of symmetry can exist in optically active modifications. The optical activity is caused by a slight difference in the indices of refraction for polarized light and results from the dissimilar interaction of the valency electrons in the atoms of the two optically active molecules with the photons of the polarized radiation. Both sign and magnitude of the rotation observed are largely determined by molecular structure.

Stereochemistry of amino acids.

Cyclic Acetals of Ketoses

The reaction of the tetranuclear rare earth metal polyhydrido complexes {Cp'Ln(mu-H)2}4(THF) (Cp' = C5Me4SiMe3, Ln = Y (1a), Lu (1b)) with carbon monoxide (1 atm) yielded ethylene and the corresponding tetraoxo cubane complexes (Cp'Ln)4(mu3-O)4 (Ln = Y (5a), Lu (5b)). Stepwise formation of some key reaction intermediates, such as oxymethylene complexes (Cp'Ln)4(mu-OCH2)(mu-H)6(THF) (Ln = Y (2a), Lu (2b)), enolate species (Cp'Y)4(OCH=CH2)(mu-O)(mu-H)5(THF) (3), and dioxo complex (Cp'Y)4(mu3-O)2(mu-H)4(THF) (4), was confirmed. The molecular structures of 2a, 4, and 5b were determined by X-ray diffraction studies.

Hydrogenation of carbon monoxide by tetranuclear rare earth metal polyhydrido complexes. Selective formation of ethylene and isolation of well-defined polyoxo rare earth metal clusters.

Karl Freudenberg

Papers

Zur Kenntnis der Aceton-Zucker, IV.: Versuche mit Galaktose und Mannose

Die Konflguration des Alanins. (4. Mitteilung über sterische Reihen)

Raumisomere Catechine IV

Ein Verfahren zur Kennzeichnung verschiedenartiger Hydroxylgruppen. Seine Anwendung auf das Lignin

Zur Kenntnis der Aceton-Zucker, VIII.: Eine neue Amino-glucose