2-Amino-1,3,2-benzodioxaboroles, (o-C6H4O2 > B·NR′R″)n(R′= H = R″; R′= H and R″= Me, Et, Pri, But, or Ph; and R′= R″= Me or Pri), have been prepared. Formation of dimers or oligomers, in the solid state or in solution but not in the gas phase, depends on R′ and R″. Monomers and oligomers in this and related systems are differentiated by (i) molecular weight, (ii) infrared spectral characteristics, and (iii) relative reactivities towards hydrolysis. Two related 2-amino-1,3,2-benzodiazaborolines, [o-C6H4(NH)2 > B·NR′R″]n have been obtained. Both for these and for 2-hydrazino-1,3,2-benzodioxaboroles, an unambiguous decision as to molecular aggregation is not possible. Criteria (ii) and (iii) were first established for the 2Me2NBCl2→(Me2NBCl2)2 system, and further use was made of (iii) to establish that the kinetics of dimerisation in dilute solution in n-hexane at 25° is governed by a second-order rate expression.