(y-butyrolactone) Y一丁内酯 (δ-valerolactone) 6一戊内酯 (y-valerolactone) Y一戊内酯O O O O O O (g-butyrolactone) g －丁内酯 (d-valerolactone) d －戊内酯 (g-valerolactone) g －戊内酯