Which term refers to the conversion of one isomer into another organic compound that differs from the first in the position of a hydrogen atom and a double bond?

• A. Disproportionation
• B. Polymerization
• C. Tautomerization
• D. Isomerization

Answer: (C)

Tautomerization is the process where one isomer rapidly interconverts with another that differs by the position of a proton and a double bond. In many organic systems, especially keto-enol pairs, a hydrogen migrates (often via acid or base catalysis) from the alpha carbon to the carbonyl oxygen, causing the C=O bond to shift to C=C and the oxygen to become an OH group, with the reverse shift able to occur as well. That movement of the hydrogen and the rearrangement of the double bond describe exactly what the question specifies.

Disproportionation involves redox changes where a single species is simultaneously oxidized and reduced to form two different species, so it isn’t about proton and double-bond rearrangement. Polymerization is the formation of polymers from monomers, unrelated to isomer interconversion. Isomerization is the broad term for any interconversion between isomers, but the description here matches the more specific process of tautomerization, where proton transfer accompanies the shift of the double bond.