iota-Carrageenan was depolymerized in mild hydrochloric acid condition. Tetrabutylammonium (TBA) salt of iota-carrageenan fragments was acylated with succinic anhydride, 4-dimethylaminopyridine and tributylamine under homogeneous conditions in N,N-dimethylformamide at 80 degrees C. Investigation of FT-IR spectrum of the succinylated product showed that a monoester derivative with succinyl group was formed when iota-carrageenan reacted with succinic anhydride. The H-1 and C-13 NMR spectroscopy has been used to characterize the fine structure of O-succinyl derivative of the i-carrageenan. The C-13 and H-1 NMR chemical shifts of disaccharide unit of O-succinyl iota-carrageenan have been fully assigned using 2D NMR spectroscopic techniques. (c) 2006 Elsevier Ltd. All rights reserved.