The pseudobase behaviour of 1,3-disubstituted-1,2-dihydro-2-oxopyrimidinium cations

Abstract

OSWALD S. TEE and MASAKI ENDO. Can. J. Chem. 54, 2681Chem. 54, (1976. The title cations form pseudobases in aqueous solution as shown by their uv and pmr spectra. Of the two potential pseudobases possible when the substitution is unsymmetrical, the preferred one is that having the hydroxyl group adjacent t o the less bulky substituent. Aside from this steric influence, the pKRoH values for the pseudobases are determined by simple electronic effects since they give reasonable correlations with Taft's U* values.OSWALD S. TEE et MASAKI ENDO. Can. J. Chem. 54, 2681Chem. 54, (1976. Les cations ci-haut mentionnks forment des pseudobases en solution aqueuse tel que demontre par leurs spectres uv et rmp. Lorsque la substitution est nonsymktrique, deux pseudobases potentielles sont possibles et celle qui est prCfkr6e est celle qui posskde le groupement hydroxyle adjacent au substituant le moins volumineux. A part cette influence stkique, les valeurs de pKRoE pour les pseudobases sont dkterrninks par les effets Clectroniques simples vu qu'ils donnent des corrClations raisonnables avec les valeurs U* de Taft.[Traduit par le journal]

Reactions of the radical cations of methylated benzene derivatives in aqueous solution

“…The appearance of the radical cation in aqueous solution is conjugated with the presence of the OH adduct via the pseudobasic equilibria A, B, and C. This is analogous to the reactions of quaternary heterocyclic cations. 10,11 The radical cations can thus be treated as an acid form of the OH adduct. The formation of the protonated OH adduct (formally identical with a monohydrated radical cation) is suggested by O'Neill et al12 in order to rationalize the acid catalyzed formation of the radical cation from the OH adduct of methoxylated benzene.…”

Evidence That the (6−4) Photolyase Mechanism Can Proceed through an Oxetane Intermediate

“…Formation of 2 is fully consistent with the initial formation of an oxetane intermediate. From our observations, it is likely that oxetane 4 is so unstable that it leads to 2 either by addition of H 2 O at C6 (path b, scheme 2) or via the 1,2-dihydro-2-oxopyrimidinium cation 5 (path a, Scheme 2), which is in equilibrium 14 with its pseudobase 2. The diastereospecific formation of the C6 S isomer is in accordance with water addition on the less hindered side of the molecule.…”