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MS Spectrum and NMR Spectra

1. The presence of nitrogen in an MS spectrum produces an odd numbered molecular ion. Indicate which of these four spectra shows presence of sulfur, chlorine, bromine, iodine or nitrogen in the molecule. Suggest a molecular formula for the nitrogen-containing compound. You may indicate the relevant fragments on the spectrum. Please justify your assignments. The periodic table is at your disposal.

2. When 2-chloro-2-methylbutane is treated with a variety of strong base, the products always seem to contain two isomers (A and B) of formula C3H10. When sodium hydroxide is used as the base, isomer A predominates. When potassium t-butoxide is used as the base, isomer B predominates. The 1H and 13C NMR spectra of A and B are given attached.
a) Determine the structures of isomers A and B.
b) Explain why A is the major product when using sodium hydroxide as the base and why B is the major product when using potassium t-butoxide as the base.

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Solution Summary

1. In assigning which of the spectra contain sulfur, chlorine, bromine, iodine or nitrogen, you must first be aware of the masses and natural abundances of these elements. 2. The structure of 2-chloro-2-methylbutane is illustrated. We are told that when treated with a base, this molecule gives two isomeric products of formula C5H10. It is clear that the chlorine has disappeared and, since we are left only with a hydrocarbon, we can suppose that we are doing an elimination reaction. There are two possible orientations by which this elimination can occur. 750 words. Full illustrations.

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