Temperature dependent rate coefficients for the gas phase reactions of Cl atoms with 4-hexen-3-one and5-hexen-2-one were measured as a function of temperature (298–363 K) and pressure (500–760 Torr;N2and O2) relative to 1,3-butadiene, isoprene and 1-pentene. Gas Chromatography (GC) coupled with a FlameIonization Detector (FID) was used to measure the concentrations of the organics. The derived temperaturedependent Arrhenius expressions arek1= (2.821.76)1012exp [(1556438)/T]cm3molecule1s1andk2=(4.62.4)1011exp [(646171)/T]cm3molecule1s1. The corresponding room temperaturerate coefficients are (5.551.31)1010cm3molecule1s1and (4.141.25)1010cm3molecule1s1for the reactions of Cl atoms with 4-hexen-3-one and 5-hexen-2-one respectively. To complement ourexperimental results, computational calculations were performed for the reactions of Cl atoms with4-hexen-3-one, 5-hexen-2-one and 3-penten-2-one over the temperature range of 275–400 K usingCanonical Variational Transition state theory (CVT) with Small Curvature Tunneling (SCT) in combinationwith the CCSD(T)/6-31+G(d,p)//MP2/6-311++G(d,p) level of theory. Atmospheric implications, reactionmechanism and feasibility of the title reactions are discussed in this manuscript.