 The reverse transformation occurs much less readily; it can be induced by ultraviolet light, but not with visible light.The conversion rate is low and only 0.36 g of angelic acid could be obtained from 13 g of tiglic acid after 43-day irradiation with a 500-watt lamp.Being the "cis" isomer, angelic acid has a lower melting point and higher acid dissociation constant than tiglic acid, in accordance to usually observed trends.