Diazinanes or hexahydrodiazines are a class of nitrogen-containing heterocycles consisting of a saturated four-carbon, two-nitrogen ring. They exist in three isomeric forms depending on the relative position of the two nitrogen atoms, with 1,4-diazinanes being common.

The diazinanes have six-membered cyclohexane-like ring but with two carbons replaced by nitrogens. The three isomers of triazinane are distinguished by the positions of their nitrogen atoms, and are referred to as 1,2-diazinane, 1,3-diazinane, and 1,4-diazinane (more commonly called piperazine).