Beilstein J. Org. Chem.2019,15, 1475–1479, doi:10.3762/bjoc.15.148
considered as a prototype for a 2e-4c Woodward–Hoffmann frozen transition state. The planar rectangular shaped structure 2 with a 2e-4cbond was found not to be a minimum.
Keywords: cyclobutane dication; 2e-4cbond; frozen transition state; Woodward–Hoffmann rule; Introduction
The protonated hydrogen
.
Hypercarbon chemistry covers in addition to carbocations also carboranes, carbon-bridged organometallics, carbonyl clusters, along with others. The rapidly evolving field has been extensively surveyed [6]. In comparison, structures of the carbocations involving a two-electron four-center (2e-4c) bond are rare
. This type of bonding could occur in rigid frameworks such as in 1,3-dehydro-5,7-adamantanediyl dication (iii) [7] and pagodane dication (iv) [8]. The question is can a 2e-4cbond exist in a molecular structure involving four atoms without any rigid frameworks such as in the diprotonated hydrogen (H42
PDF
Graphical Abstract
Scheme 1:
Examples of 2e-3c and 2e-4c bonded structures.