How do I find the molecule from the 1H NMR spectrum?
(Note: proton and 1H+ are the same thing)
1. Draw a table with the following headings:
δ / ppm, integral, splitting, observations
2. Count how many peaks there are in the spectrum. (Doublets, triplets etc. count as one peak). This is how many proton environments there are.
3. Record the chemical shifts for each peak under δ / ppm. Using the data sheet (provided by your exam board), write down the possible functional group(s) for that shift under observations. (Usually you will have other forms of analysis to help assign the functional groups.)
4. Record the value of the integral/ measure their relative heights. This is the ratio of protons in each environment. Under observations, note that this is the probable number of hydrogens in that environment.
5. Record the splitting pattern. From this you know how many hydrogens are on adjacent carbon atoms - record this under observations. Remember the n + 1 rule. i.e. doublet = 1, triplet = 2 etc. and a doublet of triplets is -CHR2 and -CH2R.
6. Now it is simply a jigsaw puzzle. You have all the components and need to arrange them to fit with your above observations. Don't forget to look for lines of symmetry if there are a high number of hydrogens in the same environment. The more practice you get, the quicker you will be able to answer these questions.
