Hydrazides in organic chemistry are a class of organic compounds sharing a common functional group characterized by hydrazine core in which at least one of the hydrogen atoms is replaced by a substituent that is an acyl group. The general structure for a hydrazide is E(=O)-NR-NR₂, where the R's are frequently hydrogens. Hydrazides can be further classified by atom attached to the oxygen: carbohydrazides (R-C(=O)-NH-NH₂), sulfonohydrazides (R-S(=O)₂-NH-NH₂) and phosphonic dihydrazides (R-P(=O)(-NH-NH₂)₂. The related hydrazines do not carry an acyl group. Some important members of this class are sulfonylhydrazides such as p-toluenesulfonylhydrazide which are useful reagents in organic chemistry such as in the Shapiro reaction and the Eschenmoser–Tanabe fragmentation. This reagent can be prepared by reaction of tosyl chloride with hydrazine.