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This value, when measured, is dependent on both temperature and frequency. Mathematically, it is the ratio of the electrical capacity of a capacitor filled with the solvent to the electrical capacity of the evacuated capacitor ( ε =C filled /C evacuated). The dielectric constant (ε), also known as the relative permittivity, of a solvent measures its ability to store electric charges. Intrinsically, the dielectric constant, dipole moment, dielectric loss, tangent delta, and dielectric relaxation time all contribute to an individual solvent’s absorbing characteristics. Many factors characterize the polarity of a solvent. In addition, the last section will discuss how to choose a solvent in a microwave-enhanced organic reaction. This chapter will discuss the theory behind solvent polarity and how it pertains to the individual solvents, their physical constants, and how they behave in a microwave field. As discussed in the previous chapter, this interaction leads to a rapid rise in temperature and faster reaction rates.

The more polar a reaction mixture is, the greater its ability to couple with the microwave energy. With microwave heating, this becomes a more significant component, as microwaves directly couple with the molecules that are present in the reaction mixture. One of the most important characteristics of a solvent is its polarity. Most reactions take place in solution, and therefore, choice of solvent can be a crucial factor in the outcome of a reaction. Solvents play a very important role in organic synthesis. The more efficient a solvent is in coupling with the microwave energy, the faster the temperature of the reaction mixture increases. Safety Considerations for Microwave Synthesis.Setting Temperature, Time, and Power in Microwave Synthesis.Getting Started with Microwave Synthesis.Nucleophilic additions and substitutions.Organometallic cross-coupling reactions.Synthetic Applications for Microwave Synthesis.Solvent and Solvent Free (Neat) Reactions in Microwave Synthesis.Organic Solvents for microwave synthesis.What type of reactions are effected by microwave heating?.How do microwaves increase reaction rates?.Theory of Microwave Heating for Organic Synthesis.