Utilising a novel solution-state NMR method for analysis of bulk crystalline celluloses , it was possible to follow the DS and regioselectivity of acetylation of commercial freeze-dried Southern Pine cellulose nanocrystals (FD-CNCs, H2SO4-hydrolysed), using a combination of 13 C-1 H HSQC, 1 H and diffusion-edited 1 H NMR spectroscopy. Reactions were performed in a simple atmospheric-pressure reaction vessel, with dry FD-CNCs exposed to Ac2O vapour (Figure ). Considering our FD-CNCs were derived from Southern Pine, the Fernandes et al. 24-chain rhomboid model for softwood serves as the only published softwood model . Using this model, full 6-OH surface acetylation corresponds to a bulk degree of substitution (DS) of 0.33. By gas-phase acetylation of the FD-CNCs over a period of 32 days at room temperature, the combination of 1 H NMR (including peak-fitting to determine DS, SI-Section S2) and diffusion-edited 1 H NMR showed a steady increase to a DS of 0.29 with visibly high regioselectivity for 6-OH acetylation (Figure ). This value is rather close to the value of 0.24 for the succinylation of hardwood-based cellulose nanofibrils (CNF), using a novel regioselective aqueous-based method . predicted for full 6-OH surface acetylation of a 24-chain rhomboid softwood elementary fibril model .