A comparative study of 5,5-dimethyl-l-pyrroline 1-oxide (DMPO) and its 2-methyl-substituted analogue (2-Me-DMPO) has revealed their contrasting reaction pathways of oxaziridine and lactam (pyrrolidone) formation. The initial photoexcitation populates the second excited singlet states (S-2) in both the systems with S-0-S-2 transition moment value of 3 D (oscillator strength 0.4); this subsequently undergoes (S-0/S-1) conical intersection through a structure having a CNO-kink and situated around 35-40 kcal/mol below the vertically excited geometry of the first excited singlet state (S-1). This conical intersection is found to be responsible for the formation of the oxaziridine photoproduct in these systems. In DMPO, this oxaziridine eventually forms the corresponding lactam compound through a [1,2]-H shift after overcoming a barrier of 35 kcal/mol and following the imaginary frequency of 1517i cm(-1). The reverse thermal process of parent nitrone formation proceeds through a transition state situated at 60 kcal/mol above the oxaziridine geometry, and the corresponding imaginary frequency is 1514i cm(-1). On the