Once a fraction or component of an essential oil or extract has been isolated, its identity needs to be determined. A familiar or common chemical is usually considered to be positively identified if its retention time on a given GC phase and its mass spectrum match those of a reference material. However, the identification of some materials with similar mass spectra, such as the sesquiterpenoids, requires retention times on two GC phases of different polarity. If the mass spectrum of a chemical is not in the reference libraries available and its structure cannot be conclusively deduced from its mass spectrum, then it must be purified and analysed by other spectroscopic techniques, such as NMR, IR or UV spectroscopy.

The advantage of NMR over MS is that the spectra produced are usually fully interpretable. A number of different experiments can be carried out using ’HNMR and 13CNMR, which normally generate enough data on the relationship of atoms within the molecule for the molecular structure to be elucidated. However, the exact structure and absolute configuration of a new natural material can only be deter­mined by either complete synthesis or X-ray crystallography. Total synthesis of the material for comparison with the isolate is very time­consuming and may be very complicated for some complex natural materials and X-ray crystallography is an expensive technique only applicable to crystalline solids. NMR is, therefore, the most revealing analytical technique available for fragrance materials.

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