As discussed in Section 1, addition of carbon to the side-chain is a potential strategy for forming diesel-range lactones. Figure plots the YSIs for 4-x-L lactones as a function of the number of carbons in the side chain (= x-4). The YSI jumps significantly from no side chain (4-4-L) to a methyl side chain (4-5-L). As the side chain grows longer, the YSI continues to increase, but by a smaller increment. The linear fit shows that this increment is about 3.7 YSI units per carbon atom. Figure compares the YSIs measured for the lactones to predictions with a group contribution method (GCM) . The GCM decomposes the target molecule into a series of carbon-centered groups, where each group is defined by all the atoms directly bonded to the central carbon, the order of the bonds, and whether the carbon atom is part of a ring. Then the YSI is estimated from: where Cj is the characteristic contribution to YSI from group j, Nj is the number of occurrences of group j in the target molecule, and the sum is over all possible groups. The values of Cj are determined by fitting Eq. (3) to a training set of molecules with measured YSIs. SI J provides further details and the raw data. Most of the data points in Fig. differ significantly from the y=x line, which shows that the YSIs are not simple functions of the atoms that are present-instead, the YSIs depend on kinetic pathways that are affected by non-nearest-neighbor interactions. Furthermore, most of the data points are below the line, which means the measured YSIs are larger than the predicted YSIs. This observation indicates that the sooting tendencies of the lactones are relatively high for compounds with two oxygen atoms.