December 8, 2009
Part 1 of the series Teaching and Learning by Spectral Data explored the difference between presenting an NMR problem set to a student in the form of an alphanumerical text or as an actual NMR spectrum. Continuing on the same problem set, another issue arises. Is the information on the elements and the 1H NMR spectrum adequate for deducing the unknown?
From the following 1H NMR spectrum, the following fragments can be deduced:
1. the multiplet at 7.24-7.57 ppm (m, 5H) indicates a mono-substituted benzene ring system,
2. the pairing of the J values and the integral information indicates a CH3-CH2 and a CH=CH (trans) fragments (tilting is also evident),
3. the chemical shift for the CH2 at 4.45 ppm indicates an adjacent oxygen atom,
4. the chemical shifts for the CH=CH fragment, 6.49 and 7.83 ppm, indicate an adjacent oxygen atom and/or benzene ring.
The elucidation cannot be completed without additional analytical or spectral data such as elemental analysis, MS, IR, 13C NMR, 2D NMR, etc.