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.
The identity of the formulae and osazones of d-mannose and d-glucose showed that the stereochemical differences were situated at the carbon atom adjacent to the aldehyde group. Fischer applied a method indicated by Pasteur in converting dextro into laevo-tartaric acid; he found that both d-mannonic and d-gluconic acids (the latter is yielded by glucose on oxidation) were mutually convertible by heating with quinoline under pressure at 140°.
In 1885 he was chosen to succeed Hans Hubner (1837-1884) in the professorship of chemistry at GÃ¶ttingen, where stereochemical questions especially engaged his attention; and in 1889, on the resignation of his old master, Bunsen, he was appointed to the chair of chemistry in Heidelberg.
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