ABSTRACT
In organic chemistry, a conjugated system is one in which there is a chain of unsaturated alternating single and double bonds as in CH2=CH--CH=CH--CH=CH2. In such polyene chains, the valence orbitals about the carbon atoms are in the sp2 hybrid electronic configuration that forms the σ -bonding frame for the chain. The remaining 2pz orbitals are aligned perpendicular to the σ bonding plane, and electrons within these orbitals are more or less delocalized over the entire molecule. In general, this delocalization decreases the overall kinetic energy of the electrons and lowers the total electronic energy of the system. Conjugated systems absorb readily in the ultraviolet and visible regions of the spectrum due to excitations of π bonding to π∗ antibonding orbitals. Generally, chains with fewer than eight conjugated bonds absorb in the UV region while increasingly longer chains absorb at longer wavelengths.
