 It crystallizes in colorless monoclinic prisms which dissolve rapidly in alcohol or hot water and slowly in cold water.Angelic and tiglic acid are "cis" and "trans" isomers of 2-methyl-2-butenoic acid, respectively.The former can be entirely converted to the latter by boiling for about 40 hours, by reaction with sulfuric and other acids, by heating with a base to a temperature above 100 °C, or simply by storing the acid for about 25 years.