Infrared and Nuclear Magnetic Resonance Spectroscopy of Chlorophyll

Publisher Summary This chapter discusses infrared and nuclear magnetic resonance (NMR) spectroscopy of chlorophyll. The absorption of visible or ultraviolet light by organic molecules is accompanied by the excitation of valence electrons to higher energy levels. Electronic excitation requires quite high-energy quanta, corresponding to light of relatively short wavelength, that is, in the ultraviolet and visible regions. Electronic transition spectra give information about the presence and nature of unsaturation, particularly conjugated double bonds and aromatic ring systems. The vibrational frequencies of molecules lie in the infrared region, and the absorption of radiation in this frequency range excites higher vibrational states. Infrared spectra yield information about stretching and bending motions of the atoms in a molecule. In theory infrared absorption bands arise from molecular motions of the molecule as a whole, but in practice, the absorption frequencies of many structural units are sufficiently independent of the rest of the molecule in which they occur to have characteristic group frequencies. NMR techniques are useful in the study of many problems. NMR data can be used for the unambiguous detection of certain functional groups and for structure determinations of organic compounds. They provide information about stereo chemical configuration and the conformation of molecules. Because the formation of intermolecular aggregates or coordination with other compounds can change the magnetic environment of a given nucleus, NMR spectroscopy is a valuable tool for the study of coordination and self-aggregation.