2.7　Solvent

UV spectra of the compounds were determined in solution，water，95% ethanol，and hexane are most commonly used.A good solvent is that it should not absorb ultraviolet radiation in the same region as the substance whose spectrum is being determined，we should know the wavelength limit of solvent itself（cutoff points）.Table 2-2 lists some common ultraviolet spectroscopy solvents and their cutoff points.Cyclohexane is ordinarily chosen as solvent in determining the ultraviolet spectra of non polar compounds，especially for aromatic compounds.The fine structures of aromatic compounds are often observed in cyclohexane.Methanol or ethanol is customarily chosen as solvent in determining the ultraviolet spectra of polar compounds.

Table 2-2　The cutoff points of common solvent

表2-2　常用溶剂的波长界限