Crystal and molecular structures of 8-bromo-6,7-dioxabicyclo[3.2.1]octane, 9-bromo-7,8-dioxabicyclo[4.2.1]nonane, and 10-bromo-8,9-dioxabicyclo[5.2.1]decane

Abstract

The crystal structures of the title saturated bicyclic [n.2.1] peroxides confirm the previous suggestion, based on n.m.r. data and mechanistic considerations, that in each compound the bromine atom is syn to the dioxygen bridge. The C–O–O–C dihedral angles are O(1), 14(1), and 45(1)° respectively, while the corresponding O–O bond lengths are 1.498(8), 1.447(8), and 1.463(7)Å. The six-, seven-, and eight-membered carbocyclic rings adopt chair, chair, and chair-chair conformations respectively. A comparison of the [3.2.1] compound with its homologues, and with 47 other cyclic or bicyclic peroxides, suggests that its O–O bond is relatively long, and that this arises because of bond angle strain primarily at the bromine-bearing carbon atom.