Reactions of n-C,H,O radicals have been investigated in the temperature range 343-503 K in mixtures of O,/N, at atmospheric pressure. Flow and static experiments have been performed in quartz and Pyrex vessels of different diameters, walls passivated or not towards reactions of radicals, and products were analyzed by GUMS The main products formed are butyraldehyde. hydroperoxide C,H803 of MW 104, I -butanol. butyrolactone. and n-propyl hydroperoxide It is shown that transformation of these RO radicals occurs through two reaction pathways, H shift isomerization (forming C,H,OH radicals) and decomposition. A difference of activation energies AE = (7 7 5 0.1 (v)) k c a h o l between these reactions and in favor of the H-shift is found, leading to an isomerization rate constant k,50m (n-C,H,O) = 1.3 X 10l2 expl -9,70O/RT) Oxidation, producing butyraldehyde, is proposed to occur after isomerization, in parallel with an association reaction of C,H80H radicals with 0, producing OOC, H,OH radicals which, after further isomerization lead to an hydroperoxide of molecular weight 104 as a main product. Butyraldehyde i s mainly formed from the isomerized radical HOCCCC' + 0, -* .-O=CCCC + HO,. since ( i ) the ratio butyraldehyde/(butyraldehyde + isomerization products) = 0.290 5 0 035 ((T) is independent of oxygen concentration from 448 to 496 K. and ( i i ) the addition of small quantities of NO has no influence on butyraldehyde formation, but decreases concentration of the hydroperoxides (that of MW 104 and n-propyl hydroperoxide). By measuring the decay of ( M W 1041 in function of I NO] added (0-22 5 ppm) at 487 K, an estimation of the isomerization rate constant OOC,H,OH -HOOC,H,OH, k , = IO"exp(-17,60O/RT) is made. Implications of these results for atmospheric chemistry and combustion are discussed. 01996