Vinyl alcohol (CH2CHOH) has been detected in emission toward Sagittarius B2N by means of its millimeter-wave rotational transitions. The simplest enol, vinyl alcohol is an important intermediate in many organic chemistry reactions. All three stable isomers of the C2H4O family, vinyl alcohol, ethylene oxide (c-C2H4O), and acetaldehyde (CH3CHO) have now been identified in the interstellar medium, as have the three members of the C2H4O2 isomeric group (Hollis, Lovas, and Jewell). These complex species cannot be produced in detected amounts by quiescent gas-phase chemistry models, and grain processes have long been envisioned. Our analysis of the abundances of the six species suggests that evaporation from grains of copious amounts of less complex species such as CH3OH and H2CO, followed by gas-phase reactions among the evaporated species, explain the high abundance of four of the species, while isomerization (on grains) of the less stable glycol aldehyde and vinyl alcohol species accounts for their lower abundances. The role of catalysis on grains remains unclear.