Electron Paramagnetic Resonance and Mass Spectroscopy Study of Spin-Trapped Radicals: Styrene—Amine Photoreactions

Abstract

The free radical intermediates from the photolysis of eleven substituted styrenes (1–11) with both tertiary and secondary amines were studied by spin trapping and the high-pressure liquid chromatography electron paramagnetic resonance (HPLC-EPR) technique. Eleven α-methylbenzyl radicals were trapped by 2-methyl-2-nitro-sopropane (MNP) and separated by HPLC. Resolution enhancement was applied to obtain long-range hyperfine splitting constants (hfsc). The nitrogen hfsc are linearly correlated with the Hammett substituent constants. The major mass spectral fragments for the trapped aminoxyl radicals (12–22) include [M+1]⁺, [M–1]⁺, [M– ^t Bu]⁺, [M– ^t BuOH]⁺, [M– ^t BuNO]⁺, and [(CH₃)₃C]⁺. The structures of 12–22 were also confirmed by chemical synthesis by adding Grignard reagent to α-phenyl-N-tert-butylnitrone (PBN) and its derivatives.