Structural isomerism

Compounds that share the same molecular formula but have a genuinely different structural formula are called structural isomers of one another, and the overall phenomenon is called structural isomerism; it is itself further split into five distinct, named sub-types. CHAIN isomerism occurs when two or more compounds share a molecular formula but have a DIFFERENT parent chain or overall carbon skeleton -- for example butane (CH3-CH2-CH2-CH3, a straight chain) and 2-methylpropane (CH3-CH(CH3)-CH3, a branched chain) are chain isomers of each other, since both share the molecular formula $C_4H_{10}$ but have visibly different carbon skeletons. POSITION isomerism occurs when compounds share the SAME functional group on the SAME underlying carbon skeleton, but that functional group simply sits at a DIFFERENT position along the chain -- for example but-2-ene (CH3-CH=CH-CH3) and but-1-ene (CH2=CH-CH2-CH3) are position isomers of each other, sharing the molecular formula $C_4H_8$ and an identical four-carbon skeleton, differing only in whether the C=C double bond sits between C2-C3 or between C1-C2. FUNCTIONAL GROUP isomerism occurs when compounds share a molecular formula but carry entirely DIFFERENT functional groups from one another -- for example dimethyl ether (CH3-O-CH3, carrying an ether functional group) and ethanol (CH3-CH2-OH, carrying an alcohol functional group) are functional group isomers, both sharing the molecular formula $C_2H_6O$ despite belonging to completely different chemical families. METAMERISM occurs when compounds share BOTH the same molecular formula AND the same functional group as each other, but distribute their carbon atoms UNEQUALLY on the two sides of that shared functional group -- for example ethoxyethane (CH3-CH2-O-CH2-CH3, with two carbons on each side of its ether oxygen) and methoxypropane (CH3-O-CH2-CH2-CH3, with one carbon on one side and three carbons on the other side of its ether oxygen) are metamers of each other, both sharing the ether functional group and the molecular formula $C_4H_{10}O$. TAUTOMERISM occurs when a SINGLE compound genuinely exists, in practice, as a rapidly-interconverting mixture of two (or more) structurally distinct forms called tautomers -- in almost every case, this rapid interconversion happens because a single proton (H atom) shifts back and forth from one atom of the molecule to a different atom of the very same molecule …