... Volume: Page: ... on the 2-pyrimidinethiol (1) ⇆ 2-pyrimidinethione (2) system: [UBPW91/6-31+G( d,p), 8 CNDO/2, 12 MNDO, 13 HF/3 ... 15 Recently Freeman and Po 16 investigated the tautomerization mechanisms between (1) and (2) in the gas phase and in the ...