Figure 1. Characteristic relations between molecular properties and glass transition temperature of organic compounds.

(a) Molecular corridor of molar mass plotted against volatility of 654 SOA compounds¹⁷ colour-coded by glass transition temperature (T_g) estimated with the Boyer–Kauzmann rule⁵. The upper dashed line indicates the low O:C bound of the molecular corridor (linear alkanes C_nH_2n+2 with O:C=0), the lower dotted line indicates the high O:C bound (sugar alcohols C_nH_2n+2O_n with O:C=1). (b) Measured (circles) and estimated (squares) T_g of organic compounds plotted against molar mass. Organic compounds with measured T_g are from Koop et al.⁵ and Dette et al.⁵¹. The markers are colour-coded by molecular O:C ratio. (c) Predicted T_g using a parameterization developed in this study compared to measured (circles) and estimated (squares) T_g with the Boyer–Kauzmann rule. The solid line shows 1:1 line and the dashed and dotted lines show 68% confidence and prediction bands, respectively.