Question

Why is the Orange II a “colored” compound? What structural feature(s) cause it to have a rich color?

Answer 1

Dyes generally contain cyclic rings that may be aromatic or may not be. Orange 2 dye is a azo dye. There is a azo group which is connected to a sulfonated benzene ring as well as to a naphthol ring. There is a conjugation between these two ring systems through N=N bond. Due to this conjugation, Pi-Pi* transitions are possible around 480 nm which falls in the visible region. This is the reason this dye appears in orange color as a result of above mentioned pi-pi* transition.