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CSI: Chemical Scene Investigation

Stage: 5 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

For the second isomer drawing exercise:
-Don't forget the possibility of double and tripled bonds!
-Who said the molecules had to be non-cyclic? Don't forget cyclobutane and cyclopropane rings!

The IR spectrum is trying to indicate three main absorptions. Ignore any other detail that you might see.If you can't see the significance of the single absorption at 3300 cm$^{-1}$, take a look at the data table for NH and NH$_2$...

Count the number of clear peaks on the NMR spectrum to give the number of Carbon environments. Next, draw a Benzene ring, and think about how the two additional carbons must be distributed as substituents around the ring. Remember that the carbons could be attached separately, or as part of the same chain.

We reckon that you can probably draw 7 structures from all the IR and NMR data. Take the hint in the question: N-O bonds won't be present in any of them!

To use the mass spectrometry data effectively, look at your seven structures and work out a logical point for the molecule to fragment (how about cleaving a group off the Benzene ring...?). See which 3 of your structures give the requires fragment masses.

The final information that the molecule is synthesised from Aryl-NO$_2$ indicates that a Nitrogen must be directly attached to the Benzene ring. Does this eliminate two of your structures?