The parent isoindole is a rarely encountered in the technical literature, but substituted derivatives are useful commercially and occur naturally.

[3][4] The parent isoindole was prepared by flash vacuum pyrolysis of an N-substituted isoindoline.

Unlike indole, isoindoles exhibit noticeable alternation in the C-C bond lengths, which is consistent with their description as pyrrole derivatives fused to a butadiene.

[6] The degree to which the 2H predominates depends on the solvent, and can vary with the substituent in substituted isoindoles.

The commercially important phthalimide is an isoindole-1,3-dione with two carbonyl groups attached to the heterocyclic ring.