Vinyl alcohol (\( CH_2=CH-OH \)) is an unstable tautomer of acetaldehyde.
It is represented by the IUPAC name Prop-2-en-1-ol: \[ CH_3-CHOH-CH_2 \rightarrow CH_2=CH-OH. \]
Explanation: But-2-en-2-ol does not match the structure of vinyl alcohol. Prop-2-en-1-ol matches the structural and chemical characteristics of vinyl alcohol.