Relative rate-studies of the reactions of 1-butoxy radicals have been carried out using a 47L static reactor with detection of end products by FT-IR spectroscopy. Experiments were performed at 700torr total pressure and over the temperature range 253–295K. The chemistry of 1-butoxy is characterized by a competition between reaction with oxygen CH 3 CH 2 CH 2 CH 2 O+O 2 →n-C 3 H 7 CHO+HO 2 (R2), which yields butanal and isomerization CH 3 CH 2 CH 2 CH 2 O→CH 2 CH 2 CH 2 CH 2 OH (R3), to form a hydroxylated carbonyl-product. A reference spectrum attributed to the product of 1-butoxy isomerization was obtained and used to determine the competition between 1-butoxy isomerization versus reaction with oxygen. The results indicate that isomerization is the dominant fate of 1-butoxy radicals at ambient temperature and pressure and that its importance decreases with decreasing temperature. The rate-coefficient ratio k 3 /k 2 (moleculecm −3 )=5.5×10 23 exp[(−25.1±0.9kJmol −1 )/RT] was obtained. This agrees with other estimates based on methods without monitoring of the isomerization product.