11.1 : エーテルの構造と命名法

Ethers, represented by the general formula C_nH_2n+2O , are organic compounds that contain an oxygen atom bonded to two alkyl, aryl, or vinyl groups.

Accordingly, ethers can be symmetrical, with identical groups on either side of the oxygen, or asymmetrical, with two different groups.

The oxygen atom in ethers is sp³ hybridized and forms σ bonds with the carbon atoms from the R groups.

Typically, ethers exhibit a bent geometry like alcohols, with the carbon–oxygen–carbon bond angle approximating the tetrahedral angle of 109.5 degrees. For example, in dimethyl ether, the bond angle is 110.3 degrees.

Common names of ethers are derived by listing the names of each R group attached to the oxygen in alphabetical order, followed by the word ‘ether’.

For example, ethyl methyl ether and methyl phenyl ether have their hydrocarbon groups listed alphabetically, followed by ‘ether’. For identical groups, ‘di’ is prefixed to the group’s name.

The IUPAC names of ethers are derived by identifying the larger R group as the parent chain and the remaining as an ‘alkoxy’ substituent.

For example, the IUPAC names of methoxy ethane and methoxy benzene have ethane and benzene as the parent chain and the smaller groups as the alkoxy substituent. For symmetrical ethers, either group can be the parent—for example, ethoxy ethane.

For more complex ethers with branching or multiple substituents, like 2-chloro-1-ethoxy-propane and 4-ethoxy-1-cyclohexene, locants are assigned to give the lowest possible number to all the substituents.

Cyclic analogs of ethers, or cyclic ethers, have the oxygen atom present in a saturated ring.

The IUPAC names for cyclic ethers use the prefix ‘oxa’ before the name of the hydrocarbon ring system. For example, oxacyclopropane and oxacyclopentane.

Alternatively, terms like “oxirane”, “oxetane”, “oxolane”, and “oxane” are also used to indicate the ring sizes from three to six, respectively.