Recent single pulse shock tube experiments on the mechanisms and rates of reaction of hydrogen atoms with unsaturated compounds are described. Attention is focused on the determination of the rate constants for the abstraction of hydrogen atoms from the resonance weakened bond and the displacement of substituent groups at the site of hydrogen addition. The experimental procedure is demonstrated via measurements of the rate constant for hydrogen atom attack on mesitylene, &agr;,&agr;,&agr;, trifluorotoluene and o‐chlorophenol). The following rate expressions have been determined. k(H+(CH3)3C6H3=H2+(CH3)2C6H3CH2)=3.7×1011exp(−4342/T) l/mol‐s k(H+(CH3)3C6H3=CH3+(CH3)2C6H4)=6.7×1010exp(−3255/T) l/mol‐s k(H+CF3C6H5=CF3+C6H6)=5.2×1010exp(−483l/T) l/mol‐s k(H+o–ClC6H4OH=OH+ClC6H5)=3.2×1010exp(−4307/T) l/mol‐s k(H+o–ClC6H4OH=Cl+C6H5OH)/k(H+o–ClC6H4OH=OH+C6H5Cl) =1.05. Past work is summarized and general trends are noted.