If (R1) occurs, the CO2 is inert and will not lead to soot, but the other product CaHb can grow to larger hydrocarbons and eventually soot. If (R2) occurs, the oxygen atoms in the products CcHdO and CeHfO interferes with either of them growing to soot. Thus, while (R1) will reduce soot formation compared to a regular hydrocarbon fuel, (R2) uses the oxygen atoms more efficiently and will reduce soot formation even more. The ReaxFF results in Fig. show that (R1) dominates for a range of lactones. The distribution of alkenes varies among the lactones, with 4-4-L producing mostly propene (light blue lines), 5-5-L producing mostly ethylene (red lines), and 4-5-L producing mostly butenes (dark blue lines). These trends may explain some of the differences observed between the lactone YSIs. For example, molecules that decompose primarily to ethylene (e.g., n-alkanes) usually have lower sooting tendencies than molecules that decompose to larger alkenes (e.g., branched alkanes) , so the preferential formation of ethylene from 5-5-L could explain why it has a much lower YSI than 4-5-L.