We measured reactions of butenedial, an atmospheric dicarbonyl, in aqueous mixtures that mimic the conditions of aerosol particles. Major reaction products and rates were determined to assess their atmospheric relevance and to compare against other well-studied dicarbonyls. We suggest that the structure of the carbon backbone, not just the dominant functional group, plays a major role in dicarbonyl reactivity, influencing the fate and ability of dicarbonyls to produce brown carbon.