Radical chemistry has in recent years been exploited to develop novel, useful methods to probe gas-phase structures with mass spectrometry. Radical-directed dissociation and photoelectron-transfer dissociation are two characteristic techniques within this category of structural analysis that facilitate bond-selective fragmentation. They provide sensitive detection of otherwise difficult to observe phenomena such as isomerization of amino acids, zwitterionic bridging, and spatial proximity in protein structure. Herein, insight into common connections between these experiments is discussed. The principles and energetics of radical chemistry are examined in detail, including fragmentation and migration of radical sites.