Supersonic molecular jet spectroscopy

If two different three-dimensional arrangements in space of the atoms in a molecule are interconvertible merely by free rotation about bonds, they are called conformationsIf they are not interconvertible, they are called configurations Configurations represent isomers that can be separated, as previously discussed in this chapter. Conformations represent conformers, which are rapidly interconvertible and are thus nonseparable. The terms conformational isomer and rotamer are sometimes used instead of conformer . A number of methods have been used to determine conformations. These include X-ray and electron diffraction, IR, Raman, UV, NMR, and microwave spectra, photoelectron spectroscopy, supersonic molecular jet spectroscopy, and optical rotatory dispersion (ORD) and CD measurements. Some of these methods are useful only for solids. It must be kept in mind that the conformation of a molecule in the solid state is not necessarily the same as in solution. Conformations can be calculated by a method called molecular mechanics (p. 178). 

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