Phenylhydrazide rule

The directions of the optical rotations of the lactones (presumably gamma lactones) and phenylhydrazides of the four 3-deoxypentonic acids are in agreement with those predicted, on the basis of the assigned configurations, by the lactone and phenylhydrazide rules. 

The configuration of C2, the tertiary carbon atom, of o[ -D-isosaccharinic acid has not been established. Unfortunately, application of qualitative rules of configuration based on optical rotation affords disagreeing conclusions in this instance. The positive optical rotation of the phenylhydrazide would indicate the d configuration for C2 on the basis of the phenylhydrazide rule. On the other hand, the reported negative optical rotation of the acid amide would assign the l configuration to this carbon atom on the... 

During the interval between Vongerichten s and Schmidt s investigations, there were discovered several empirical rules through which the configuration of the a-carbon atom of many a-hydroxycarboxylic acids may be inferred. Schmidt applied three of these generalizations, the salt-acid rule and the phenylhydrazide and amide rules, to the appropriate derivatives of apionic acid Table I shows the comparisons which he published. 

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