Strategic Approach to Analyzing Mass Spectra and Solving Problems

158°C to 159°C. Table 4.1 reproduces the type of information that the computer would display as a hit list. Notice that the information inclndes the name of each compound that the computer has used for matching, its molecular weight and molecnlar formula, and its Chemical Abstracts Service (CAS) Registry number. [Pg.191]

The information in Table 4.1 indicates that the unknown liquid is most likely l-chloro-2-methylbenzene since the probability of a correct match is placed at 94%. It is interesting to note that the meta and para isomers show probabilities of 70% and 60%, respectively. It is tempting to simply accept the results of the computer-based library search as correct, but the method is not an absolute guarantee that the identity of a sample has been correctly determined. A visual inspection of the experimental and library spectra must be included as part of the process. A computer can compare a mass spectrum it has determined with the spectra in these databases. [Pg.191]

Like any other problem involving the correlation of spectral data with structure, having a weU-defmed strategy for analyzing mass spectra is the key to success. It is also true that chemical intuition plays an important role as well, and of course there is no substitute for practical experience. Before diving into the mass spectrum itself, take an inventory of what is known about the sample. Is the elemental composition known Has the molecular formula been determined by exact mass analysis What functional groups are present in the compound What is the sample s chemical history For example, how has the sample been handled From what sort of chemical reaction was the compound isolated And the questions can continue. [Pg.191]

After analysis of the molecular ion cluster, examine the high mass peaks in your spectrum and determine whether the mass losses are odd or even. If an even number of nitrogens are present (zero is even), odd mass losses correspond to simple homolytic cleavages, and even mass losses [Pg.191]

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. [Pg.191]

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