The ring structures of selected dioxopiperazines and their sulphur-containing analogues undergo remarkable geometry changes during enolization as established by semiempirical (AM1) and non-empirical (HF/3-21G) MO computations. The dienols attempt to lose their "pseudo-anti-aromatic" or "anti-aromatoid" character by three plausible mechanisms: (i) changing the CX bond length; (ii) changing the NH out-of-plane angle; (iii) changing the planarity/non-planarity of the six-membered ring. The effectiveness of these three mechanisms is discussed for cyclo(Gly-Gly), cyclo(Ala-Ala), cyclo(Pro-Pro) and their dithio derivatives cyclo(Glyt-Glyt, cyclo(Alat-Alat), cyclo(Prot-Prot).
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry