Temperature dependent rate coefficients for the gas phase reactions of Cl atoms with 4-hexen-3-one and 5-hexen-2-one were measured as a function of temperature (298-363 K) and pressure (500-760 Torr; N2 and O2) relative to 1,3-butadiene, isoprene and 1-pentene. Gas Chromatography (GC) coupled with a Flame Ionization Detector (FID) was used to measure the concentrations of the organics. The derived temperature dependent Arrhenius expressions are k1 = (2.82 ± 1.76) × 10-12 exp [(1556 ± 438)/T] cm3 molecule-1 s-1 and k2 = (4.6 ± 2.4) × 10-11 exp [(646 ± 171)/T] cm3 molecule-1 s-1. The corresponding room temperature rate coefficients are (5.55 ± 1.31) × 10-10 cm3 molecule-1 s-1 and (4.14 ± 1.25) × 10-10 cm3 molecule-1 s-1 for the reactions of Cl atoms with 4-hexen-3-one and 5-hexen-2-one respectively. To complement our experimental results, computational calculations were performed for the reactions of Cl atoms with 4-hexen-3-one, 5-hexen-2-one and 3-penten-2-one over the temperature range of 275-400 K using Canonical Variational Transition state theory (CVT) with Small Curvature Tunneling (SCT) in combination with the CCSD(T)/6-31+G(d,p)//MP2/6-311++G(d,p) level of theory. Atmospheric implications, reaction mechanism and feasibility of the title reactions are discussed in this manuscript. © 2017 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.