In previous sections of this text the structural formulas of hundreds of organic compounds have been reported, often with very little supporting evidence. These structures, and millions of others described in the scientific literature, are in fact based upon sound experimental evidence, which was omitted at the time in order to focus on other aspects of the subject. Much of the most compelling evidence for structure comes from spectroscopic experiments, as will be demonstrated in the following topics.
In order to "see" a molecule, we must use light having a wavelength smaller than the molecule itself (roughly 1 to 15 angstrom units). Such radiation is found in the X-ray region of the spectrum, and the field of X-ray crystallography yields remarkably detailed pictures of molecular structures amenable to examination. The chief limiting factor here is the need for high quality crystals of the compound being studied. The methods of X-ray crystallography are too complex to be described here; nevertheless, as automatic instrumentation and data handling techniques improve, it will undoubtedly prove to be the procedure of choice for structure determination.
The spectroscopic techniques described below do not provide a three-dimensional picture of a molecule, but instead yield information about certain characteristic features. A brief summary of this information follows:
Spectroscopy Resources |
| Introduction to Mass Spectrometry |
Prepared at Vanderbilt University. A much more advanced treatment than provided in this text. |
| Ionization Methods in Mass Spectrometry |
Prepared by JEOL. A more thorough discussion of ionization than provided in this text. |
| NMR Tutorial and Spectroscopy Problems |
Prepared at Imperial College. A more advanced tutorial than that provided in this text. The associated problems all involve nmr spectroscopy, but also use data from infrared and mass spectrometry. |
| NMR Spectroscopy-A Virtual Text |
Prepared by Joseph Hornak, Rochester Institute of Technology. An exceptional introduction to modern nmr spectroscopy. More advanced than this text. |
| NMRShiftDB-an NMR database. |
This database of organic structures and their nuclear magnetic resonance (nmr) spectra is hosted by the Max Planck Institute of Chemical Ecology in Jena. |
| NMR meets Musicians |
A clever and informative site from the University of Erlangen-Nuremberg, Institute of Organic Chemistry |
| Spectroscopy Tools |
A useful site providing information for NMR, IR and mass spectroscopy. Created at the University of Potsdam. |
| More Spectroscopy Tools |
A nice collection of applications for interpreting NMR, IR and mass spectra. Created at Colby College. |
| Spectra Data Base |
A large and very useful collection of MS, NMR, IR, Raman & ESR spectra. This page is hosted by SDBS, Japan. |
Spectroscopy Problems |
| 64 Graded Problems |
Compiled at Notre Dame. A very nice collection of problems using all the spectroscopy methods discussed here. |
| 72 Graded Problems |
Compiled at UCLA. An outstanding collection of unknowns requiring the interpretation of nmr spectra & some ir. Solutions are provided. A general discussion of nmr and its uses is given. Some advanced techniques not discussed in this text are used. |
| NMR Spectroscopy Problems |
Compiled at the University of Sydney. Thirteen problems and discussion answers are presented. |
| More NMR Spectroscopy Problems |
This Frankland & Marshall College site also has an excellent list of nmr references |
| Infrared Spectroscopy Problems |
Prepared at Colby College. This is the Netscape version. |