The mechanism of photochemical reactions in cyclohexene and cyclohexadiene under UV radiation differs due to the presence of different types of chemical bonds and the electronic configuration of these molecules. Let's discuss the photochemical reactions of both compounds separately.1. Cyclohexene:Cyclohexene is an alkene with one carbon-carbon double bond C=C . When exposed to UV radiation, the energy from the radiation is absorbed by the electrons in the double bond, promoting them to a higher energy state * . This process is called to * transition. The excited state molecule is highly reactive and can undergo various reactions, such as cis-trans isomerization, dimerization, or oxidation.Mechanism for cis-trans isomerization:1. Absorption of UV radiation by the electrons in the double bond, leading to the formation of an excited state molecule.2. Rotation around the double bond, which is now possible due to the excitation of the electrons.3. Relaxation of the excited state molecule back to the ground state, resulting in the formation of a new isomer either cis or trans .2. Cyclohexadiene:Cyclohexadiene is a diene with two carbon-carbon double bonds C=C in a six-membered ring. The presence of two double bonds in conjugation allows for extended delocalization of electrons, which results in a lower energy gap between the and * orbitals. When exposed to UV radiation, the electrons in the double bonds can undergo to * transition, similar to cyclohexene. However, due to the presence of two double bonds, cyclohexadiene can undergo various photochemical reactions, such as electrocyclic reactions, cycloaddition reactions, or rearrangement reactions.Mechanism for electrocyclic reaction 6 electrocyclization :1. Absorption of UV radiation by the electrons in the double bonds, leading to the formation of an excited state molecule.2. The excited state molecule undergoes a conrotatory or disrotatory ring closure, depending on the orbital symmetry and the reaction conditions.3. Relaxation of the excited state molecule back to the ground state, resulting in the formation of a new cyclic compound e.g., cyclohexene or benzene .In summary, the mechanism of photochemical reactions in cyclohexene and cyclohexadiene under UV radiation differs due to the presence of different types of chemical bonds and the electronic configuration of these molecules. Cyclohexene mainly undergoes cis-trans isomerization, while cyclohexadiene can undergo various reactions, such as electrocyclic reactions, cycloaddition reactions, or rearrangement reactions, due to the presence of two conjugated double bonds.