text: In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two organyl groups (e.g., alkyl or aryl). They have the general formula , where R and R′ represent organyl groups (e.g., alkyl or aryl). Ethers can again be classified into two varieties: if the organyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anaesthetic diethyl ether, commonly referred to simply as "ether" (). Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.