Photochemistry in the Laboratory

Photochemistry is used advantageously in the organic chemistry lab to transform certain organic compounds into other desired organic compounds. Knowledge gained by photochemical studies is used to predict the outcome of such reactions and to plan synthetic sequences to obtain a desired compound.

A compound is dissolved in an appropriate solvent and irradiated with a source of uv radiation. When low intensity radiation is needed, an ordinary incandescent bulb can be used. When an intense source of uv radiation is needed, a sunlamp or lamp specially designed for photochemical applications is used. When intense sources of uv radiation are used, lab personnel must protect their eyes from uv damage.

One experiment that has been done in the undergraduate Organic Laboratory is the photochemical conversion of benzophenone to benzopinacol. Benzophenone is dissolved in 2-propanol and placed in a glass flask and left in the window in the sunlight for a week. After this time, the reaction has gone nearly to completion and crystals of benzopinacol have formed in the flask. The student then filters out the crystals and confirms the structure by melting point and spectral analysis. In the research lab, occasionally some steps in the multi-step synthesis of complex organic molecules are carried out photochemically.

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