ABSTRACT
Free radicals are independently existing species that possess an unpaired electron and normally are highly reactive with short lifetimes. A carbon-based free radical typically has sp2 hybridization and has a general structure that can be represented in several ways, such as
where R1, R2 and R3 represent atoms or molecular fragments attached to the carbon atom bearing the unpaired electron. Structure (i) is a spatial representation in which the thin lines are in the plane of the paper, the dashed line is at 90° to and protruding behind the plane of the paper and the solid wedge is at 90° to and protruding forward from the plane of the paper; the single residual p-orbital is represented by the two lobes above and below the C atom and contains the unpaired electron which is represented by a ‘dot’ and circulates around both lobes of the p-orbital (but in structure (i) is shown at an instant in time when it is present in the upper lobe). Structure (ii) is a simplified version of (i) in which the lobes of the p-orbital are omitted, and structure (iii) is an even simpler non-spatially accurate representation in which correct bond angles are neglected. The latter two representations of free radicals are most common.
