The structures of the free-radical scavenger 1, 1, 3, 3-Tetramethylisoindolin-2-yloxyl, and of the alkoxy amine derivative 5-(1, 1, 3, 3-Tetramethylisoindolin-2-yloxy)- 1-vinylpyrrolidin-2-one

The structures of the title nitroxide, C₁₂H₁₆NO (1), and the alkoxy amine derivative, C₁₈H₂₄N₂O₂ (2), have been determined by single-crystal X-ray structural analyses. Crystals of (1) are monoclinic, space group Cc with a 11•585(6), b 11•697(10), c 16•753(8) Å, β 94•33(6)°, Z 8; R was 0•064 for 1226 independent reflections. The -C(NO)C- group is essentially planar (sum trigonal angles 359•9, 359•9°), as is the five-membered ring. The N-O distances are 1•249(6), 1•252(8) Å. Crystals of (2) are monoclinic, space group P2₁/c c, a 8•295(2), b 13•567(5), c 15•294(3)Å, β 98•82(2)°, Z 4; R was 0•051 for 1445 independent reflections. By contrast to (1) the geometry about the nitrogen atom is pyramidal (sum trigonal angles 328°), and the corresponding five-membered ring has an envelope conformation with a nitrogen displacement of 0•45 Å. The N-O distance is 1•439(4) Å. The high-resolution solid state ¹³C n.m.r. spectrum of (2) is discussed in relation to the X-ray structure.