Single-crystal electron paramagnetic resonance studies of the action of red light on the needle form of humulene nitrosite, C15H24N2O3: the first nitroxide radical formed in the photochemical reaction

Abstract

Spin-Hamiltonian parameters, in an arbitrarily chosen crystal xyz frame, have been extracted from e.p.r. spectra of the first nitroxide radical that is obtained when a single crystal of the needle form of humulene nitrosite (1) is briefly irradiated with red light. Diagonalization of the spin-Hamiltonian matrices, followed by transformation into the abc frame of the monoclinic unit cell, shows that this first radical is a monoalkyl nitroxide H(R)N[graphic omitted]O, compound (7). The anisotropic components of the magnetic parameters show that this radical undergoes marked thermal motion in the crystal, so that the crystallographically distinguishable molecules in this solid can not be distinguished by e.p.r. methods at 290 K.