Detergent compositions containing certain acetals or ketals which hydrolyze upon exposure of surfaces washed in solution of said compositions to a reduction in pH, thereby releasing a fragrance which is characteristic of one or more of the hydrolysis products. The acetals and ketals themselves also form part of the invention; they have a molecular weight of at least about 350; a ClogP of about 4, and a half-life of less than 60 minutes when measured at pH=0 by the pro-fragrant hydrolysis test.