Highly carcinogenic bis-chloromethyl byproducts containing this functional group limit industrial use of the Blanc chloromethylation. Potassium iodide can be used to test for explosive peroxides in stocks of compounds with this group that have been exposed to air. Cryptands are 3D analogues of a cyclic version of these (10[1])groups useful for complexing alkali metals and for acting as phase transfer catalysts. This group’s ability to complex Mg2+ ions and general non-reactivity allows molecules with this group to be used to store Grignard reagents. Cyclic molecules containing this group include furans (10[1])and molecules named after crowns. For 10 (10[1])points, name this functional group consisting of an oxygen flanked by two R groups, whose diethyl variety can be used as an anesthetic. ■END■ (10[2])