A notable amount of research has been placed toward understanding the roles of benzoquinone (Q) and hydroquinone (HQ) in the chemistry and toxicity of cigarette smoke. To further understanding of the roles of these compounds in cigarette smoke, a series of reactions were performed wherein the levels and chemistries of Q and HQ were monitored after having been added to selected phases of the mainstream smoke from 2R4F cigarettes. Through the application of both fondamental organic chemistry reaction mechanistic principles and qualitative analysis of smoke chemistry, a new reaction pathway for mainstream smoke components was elucidated. During the course of these investigations, the presence of a product from a Diels-Alder reaction between a 2R4F cigarette mainstream smoke component and Q was discovered. Data from carbon-13 nuclear magnetic resonance (13C NMR), gas chromatography-atomic emission detection (GC-AED), and gas chromatography-mass selective detection (GCMSD) revealed a Diels-Alder reaction product resulting from the reaction of benzoquinone (Q), a dienophile, and 1,3-cyclopentadiene, a diene, to yield tricyclo[6.2.1.02.12,7] undeca-4,9-diene-3,6-dione, more commonly referred to as cyclopentadienebenzoquinone. The reaction between Q and 1,3-cyclopentadiene was observed to have occurred when fresh mainstream vapor phase smoke (MSVP) from a 2R4F cigarette, captured in acetone, was subsequently treated with Q. Other 13C containing species were detected but inadequate signal to noise values prevented structural assignments. Accompanying the Diels-Alder reaction was an additional reaction of Q to form hydroquinone (HQ). These reactions provide additional information on the complexity of cigarette smoke, particularly as it relates to possible reactions involving Q and HQ and other cigarette smoke components.