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Mass Spectroscopy 2 - Spectroscopy Lab Sam Keath CHEM...

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Spectroscopy Lab Sam Keath CHEM 2642L-265 Georgia Perimeter College Instructor: Dr. David Jeffrey August 30, 2010
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Introduction The purpose of this experiment was to determine the identity of two unknown compounds using IR, NMR, and mass spectra. According to McCurry “The mass spectrum of a compound serves as a kind of molecular fingerprint.” Each unique compound has its own distinctive fragmentation pattern. If you have 2 samples which are constitutional isomers having the same molecular weight, then you can determine the way in which the atoms were bonded by their fragments. In essence, we are working backwards to determine the bonding structure of the whole molecule from its individual fragments or ions. The mass spectrometer breaks up the molecule in different ways depending on how it was bonded. That is the main factor which affects the appearance of the graph obtained from this instrument—the bonding of the atoms within the molecule. The graph is called the mass spectrum and this is how the mass spectrum is read: the horizontal x axis tells us the mass-to-charge ratio of the molecule fragment m/z and the y axis tells us its percent abundance. A mass spectrum can only tell us about the molecule fragments, the mass-to-charge ratio, and the percent abundance. The lightest molecule fragments will show up on the far left. The peak farthest to the right tells us the abundance and mass of the whole molecule before fragmentation, the molecular ion M+.
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