NMR Approach?

[emminent]

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Hey guys,

So I've been watching Chad's explanation back and forth on H NMR and I still keep getting confused with the triplets/singlets/doublets/etc. C NMR is so much easier to understand b/c you just count carbons that are not symmetrical to each other. I just don't get H NMR so how do you guys approach these problems?

Thanks

 

[elhammy]

1) Draw the structural formula
2) Identify any planes of symmetry
3) Locate all hydrogen environments (meaning anywhere you see a hydrogen attached)
4) The splitting pattern (singlet, doublet, .....) is just +1 to the # of H atoms surrounding that specific hydrogen environment (n+1 rule)

Take Propane for example (C3H8):
1) CH3CH2CH3
2) It has a line of symmetry down the middle so hydrogens attached to carbon 1 and 3 will have the same representation on the H-NMR graph.
3)Therefore, you have 2 different hydrogen environments on C1/C3 & C2
4) The splitting pattern on Carbon 1 is determined by the # of H atoms on C2. You have 2 hydrogen's on C2 therefore the splitting pattern is a triplet.
Carbon 2 is the other hydrogen environment and has 6 surrounding H atoms on C1 & C3. Therefore, the splitting pattern is a septet.