Abstract
From global conformational profile and differential activation energies
of conrotatory outward and inward ring openings of all the conformers, it is
shown that (a) 3-OMe-cyclobutene must open exclusively outward, and (b) conformers
exist for 3-CHO-, 3-COMe-, and 3-NO-cyclobutenes that will open outwards as
well. All the conformers of 3-OMe-, 3-CHO-, 3-COMe-, and 3-NO-cyclobutenes are,
respectively, within 5.6, 3.2, 4.0 and 2.6 kcal/mol and, hence, abundantly
available at room temperature for reaction.