Abstract:The crystal structure of 2-(4-bromophenyl)-4-(2-fluoroethyl)-5,6-dihydro-4H-1,3,4-oxadiazine hydrochloride, a new octopamine agonist, has been established by Patterson and Fourier methods and refined to a final R value of 0.0293 for 2123 absorption-corrected observed data. The crystals are monoclinic, n = 14.336(3), b = 12.649(3), c = 6.989(1) A, P = 93.48(1)", and the space group is P2,lc. Its structural similarities with the crystal structure of the invertebrate neurotransmitter, octopamine, are described and support the hypothesis that the pesticidal properties of dihydrooxadiazines are, at least partially, due to perturbation of octopaminergic systems.Key words: dihydrooxadiazine, octopamine agonist.