The fundamental heterocyclic compound 1,4-oxazine has been generated using FVP. It is the first parent heterocycle among all the possible isomeric oxazines, thiazines and their heavier atom analogues to be characterised spectroscopically, and is shown to exist in solution entirely as the 4H-isomer. X-ray structure determination of the N-Boc precursor shows significant deviations from theoretically predicted geometric parameters.