The carbonyl oxygen may also be replaced by the oxime group,: N OH; thus the acids yield the hydroxamic acids, R C(OH): NOH, and the acid-amides the amidoximes, R C(NH 2): NOH.
The aldoximes are converted by the action of dehydrating agents into nitriles: RCH: NOH-->R C: N+H 2 0.
Beckmann, Ber., 1886, 1 9, p. 9 8 9; 188 7, 20, p. 2580), yielding as final products an acid-amide or anilide, thus: RC(:N OH)R'-RC(OH) :NR' ---> As regards the constitution of the oximes, two possibilities exist, namely >C: NOH, or > C' ?, and the first of these is presumably correct, since on alkylation and subsequent hydrolysis an alkyl hydroxylamine of the type NH 2 OR is obtained, and consequently it is to be presumed that in the alkylated oxime, the alkyl group is attached to oxygen, and the oxime itself therefore contains the hydroxyl group. It is to be noted that the oximes of aromatic aldehydes and of unsymmetrical aromatic ketones frequently exist in isomeric forms. This isomerism is explained by the HantzschWerner hypothesis (Ber., 1890, 23, p. II) in which the assumption is made that the three valencies of the nitrogen atom do not lie in the same plane.
In the absence of water, it forms salts of the type (CH 2: NOH)3 HC1 with acids.
Acetaldoxime, CH 3 CH: NOH, crystallizes in needles which melt at 47° C. On continued fusion the melting point gradually sinks to about 13° C., probably owing to conversion into a polymeric form.