Question

Combined IR Spectroscopy and Mass Spectrometry Problems Determine the molecular formula and possible structures for each unknown based on the given spectra. Use the IR Correlation Table. Note: DOU - Cs+1-0.5(#Hs-#Ns+Whalogens). SHOW YOUR WORK! 100 - 2191 Relative Intensity 10 15 20 25 30 40 35 m/z 45 50 55 60

Answer 1

From the MS spectra we can easily determine that the molar mass of our compound is 59 g/mol.

From the IR, the two most important signals are at around 3300 cm^-1, which are indicative of a primary amine. That is, we have a -NH₂ group in our molecule.

Coming back to the MS spectra, the main peak has a m/z of 30, which represents a loss of 29 from the main peak. This is probably due to an ehtyl group: -CH₂-CH₃.

Considering our molecule weights 59 g/mol and that we have 29 and 16 g/mol from the ehtyl and amino groups, respectively, what we are "missing" is: 59-16-29, which is 14. This is a -CH₂- group. This means that, putting the pieces together, the molecules must be propylamine: H₃C-CH₂-CH₂-NH₂.