As the mid-chain carbons reside in a highly crowded part of the 13 C NMR spectrum (see Fig. for POPC, Fig. of Ref. 45 for DMPC), assigning their dipolar splittings (i.e. S CH ) to the corresponding carbons is challenging. Our assignment is based on previous work that used sn-1-perdeuterated POPC to separate the sn-1 from the sn-2 carbons. Since some intra-tail ambiguity still remains, Figs. and indicate the crowded-region S CH with empty symbols.