CHAPTER VII 



Relationships between the colour and 

 constitution of carotenoids 



It has already been stressed that the yellow to violet colour of carotenoids 

 is one of their most important characteristics. It is thus not surprising that 

 repeated attempts have been made to elucidate the relationships between the 

 colour and constitution of carotenoids and to employ absorption spectra for 

 the characterisation and identification of polyene pigments. Many advances 

 in this field have been made during the last 20 years and it is possible to-day 

 to draw definite conclusions regarding the constitution of a carotenoid from 

 its absorption spectrum. Conversely, certain changes in the spectrum can be 

 predicted from a given change in structure^. 



Although carotenoids possess a relatively complex structure, the absorption 

 spectra of these pigments are comparatively simple in character. In the visible 

 region the spectrum usually consists of three, or occasionally four, absorption 

 maxima and the position of the maxima is related in a relatively simple manner 

 to the constitution of the pigments. In the ultra-violet region, the relationships 

 between constitution and spectral properties are more complicated and it is 



2W0 2500 3000 3500 UOOO 4500 



Fig. 3. Light absorption of xanthophyll in hexane solution 



5000 

 XinS 



References p. sg. 



