Lang, " Versuch einer Erklarung der Asymmetric der Gastropoder," Vierteljahrsschr.
The proof of this statement rests on the fact that if the hydrogen atoms were not co-planar, then substitution derivatives (the substituting groups not containing asymmetric carbon atoms) should exist in enantiomorphic forms, differing in crystal form and in their action on polarized light; such optical antipodes have, however, not yet been separated.
If, however, two compounds only differ with regard to the spatial arrangement of the atoms, the physical properties may be (I) for the most part identical, differences, however, being apparent with regard to the action of the molecules on polarized light, as is the case when the configuration is due to the presence of an asymmetric atom (optical isomerism); or (2) both chemical and physical properties may be different when the configuration is determined by the disposition of the atoms or groups attached to a pair of doubly-linked atoms, or to two members of a ring system (geometrical isomerism or allo-isomerism).
Of the tri-derivatives the symmetrical compounds boil at the lowest temperature, the asymmetric next, and the vicinal at the highest.
The aldehyde group reacts with hydrocyanic acid to produce two stereo-isomeric cyanhydrins; this isomerism is due to the conversion of an originally non-asymmetric carbon atom into an asymmetric one.
Lowry and Armstrong represent these compounds by the following spatial formulae which postulate a y-oxidic structure, and 5 asymmetric carbon atoms, i.e.
Since the molecule contains an asymmetric carbon atom, the acid exists in three forms, one being an inactive "racemic" mixture, and the other two being optically active forms. The inactive variety is known as paramandelic acid.
It is a colourless solid which melts at 92° C. For silicon derivatives of the amines see Michaelis, Ber., 1896, 29, p. 710; on asymmetric silicon and the resolution of dl-benzyl-ethyl-propyl-silicol see F.
It is seen that aldoses and ketoses which differ stereochemically in only the two final carbon atoms must yield the same osazone; and since d-mannose, d-glucose, and d-fructose do form the same osazone (d-glucosazone) differences either structural or stereochemical must be placed in the two final carbon atoms.3 It may here be noticed that in the sugars there are asymmetric carbon atoms, and consequently optical isomers are to be expected.
Although containing an asymmetric carbon atom it has not been resolved.
The plane projection of molecular structures which differ stereochemically is discussed under Stereoisomerism; in this place it suffices to say that, since the terminal groups of the hexaldose molecule are different and four asymmetric carbon atoms are present, sixteen hexaldoses are possible; and for the hexahydric alcohols which they yield on reduction, and the tetrahydric dicarboxylic acids which they give on oxidation, only ten forms are possible.
4,as mannose is produced by reversing the sign of the asymmetric system adjoining the terminal COH group.
If the asymmetric system adjoining the COH group, which is that introduced in synthesizing the hexose from the pentose, be eliminated, the formulae at disposal for the two pentoses are CH 2 (OH) - - - COH CH 2 (OH)+-- COH.
When such compounds are converted into corresponding dibasic acids, CO 2 H.[CH(OH)) 3.00 2 H, the number of asymmetric carbon atoms becomes reduced from three to two, as the central carbon atom is then no longer associated with four, but with only three different radicles.
This formula, which necessitates the presence of two asymmetric carbon atoms in an alkyl tetrahydroberberine, has been accepted by M.
Since the acid contains an asymmetric carbon atom, it can exist in three forms, a dextro-rotatory, a laevo-rotatory and an inactive form; the acid obtained in the various synthetical processes is the inactive form.
The normal nitrate, Bi(N03)3.5H20, is obtained in large transparent asymmetric prisms by evaporating a solution of the metal in nitric acid.
The acid sulphate, NaHSO 4, also known as bisulphate of soda, is obtained as large asymmetric prisms by crystallizing a solution of equivalent quantities of the normal sulphate and sulphuric acid above 50°.
VALERIC ACID, or [[Valerianic Acid, C4h9 C02h]], an organic acid belonging to the fatty acid series, which exists in four isomeric forms, one of which contains an asymmetric carbon atom and consequently occurs in two optically active modifications and one optically inactive modification.