2-Buten-4-olide 2-Butenoic acid gamma-lactone 2-Butenoic acid, 4-hydroxy-, gamma-lactone 2-Butenoic acid-gamma-lactone 2-Butenolide 2-Oxo-2,5-dihydrofuran 4-Hydroxy-2-butenoic acid lactone 4-Hydroxycrotonic acid gamma-lactone 497-23-4 5-17-09-00112 (Beilstein Handbook Reference) BRN 0383585 BUTENOLIDE CCRIS 5722 Crotonic acid, 4-hydroxy-, gamma-lactone (6CI,7CI) EINECS 207-839-3 Furan-2(5H)-one Isocrotonolactone NSC 197009 alpha,beta-Crotonolactone delta,alpha,beta-Butenolide gamma-Crotolactone gamma-Hydroxycrotonic acid lactone