Some dihydro-and tetrahydro-2-methyl-4-aryl-benzo-(1,5)-thiaze- pines are subjected to spectroscopic studies (NMR, IR and UV) and their conformations are discussed. The formation of the dihydro- compounds is highly selective and its conformation assumes a boat- like form. The reduction of the dihydrocompounds takes place stereospecifically with the formation of the tetrahydrocompounds which assumes a twist boat conformation. A benzalaniline system is present in these dihydro-compounds, but the N-phenyl forms a part of the heterocyclic ring system and can not rotate around the C=N bond. The angle between the planes of -C (Ar)=N- and benzoring is about 50` and conjugative effect between these two rings still can be shown.

Key words: NITROGEN HETEROCYCLICS, SPECTROGRAPHIC ANALYSIS, SULFUR HETEROCYCLICS COMPOUNDS, CONFORMATION, SEVEN MEMBER RING HETEROCYCLICS COMPOUNDS