# How many ether metamers are possible for C4H10O?

How many ether metamers are possible for $$\ce{C4H10O}?$$

According to me, the answer should be 2 but it was given 3. I know 3 structures can be made:

$$\ce{CH3—O—CH2—CH2—CH3}\tag{1}$$

$$\ce{CH3—CH2—O—CH2—CH3}\tag{2}$$

$$\ce{CH3—O—CH(CH3)2}\tag{3}$$

Structure 2 and 3 are metamers, but 1st and 3rd structures are positional isomers(?), then how the answer can be 3?

• Funny that my first answer was down voted because I right gave ethers as example of metaners apparently out of black. Lately I see more people comfortable with that. By the way I do not see much, if any, use of this particular class of isomerism which is covered by the other classifications. – Alchimista Aug 23 '19 at 13:02
• Metamer, really? Im glad to be able to say that none of my teachers or professors has ever bothered to introduce this new metacategory. – Karl Aug 24 '19 at 19:58
• Can anyone point me to a IUPAC definition of the term "metamer"? Google was unsuccessful for me, en:wp has nothing but a one -liner saying the term is obsolete, nothing on de:wp. – Karl Aug 25 '19 at 6:46
• Metamerism definition (3rd bullet) includes position isomers! – Rahul Verma Aug 26 '19 at 3:43