Summary The absorption spectra of a number of polyene derivatives of cyanoacetic acid and its esters have been measured and compared. Particular attention has been paid to the effects on the spectra of increasing the number of double bonds in conjugation with the cyano. and carboxyl groups. The effects of methyl substitution 011 the olefinic linkages have been rioted; and the spectra of mnie of the acids have been compared with those of the ...