ELECTRONIC TRANSITION
ELECTRONIC TRANSITION 1. σ-------> σ* transitions An electron is excited from the bonding σ orbital to the corresponding σ* orbital. The transition energy required is very high. This type of transition occurs below 150nm. Therefore the absorption occurs in the vacuum UV region. This type of transition occurs in saturated hydrocarbons. Thus saturated hydrocarbons do not show any absorption in the UV, visible region. Therefore they are colorless and known as UV transparent compounds. 2. π-------> π* transitions The unsaturated hydrocarbons containing double or triple bond shows this type of transition. The π ---->π* bands appear at 180-190nm in the case of aliphatic compounds and at 200-210nm in the case of simple aromatic compounds. Eg: Ethene-190nm, 1,3-butadiene – 217nm, 1,3,5-hexatriene – 247nm, Benzene- 255nm 3. n-------> π* transitions These transitions are observed in aldehydes and ketones whi...