What is compounds are considered ethers?

An ether is a compound that has two functional groups separated by an oxygen. The typical structure appears like this: R - O - R', where R and R' are the functional groups. R and R' can only be alkyl and aryl groups. Take for example the simplest ether, Dimethyl ether. The formula is given as CH3OCH3, where there are two methyl groups on each side of the ether. Notice that CH3 is a methyl group, which is an alkyl group.

Most smaller stars don't have a radiative zone.