Question

For pentan-3-one why is the splitting pattern of the peak with greatest area in the high resolution nmr spectrum a triplet and not a quintet?

Answer 1

Well, you gots `"diethyl ketone"`, `"H"_3"CCH"_2"C(=O)CH"_2"CH"_3`

Explanation:

There are TWO sets of protons observed in the `""^1H` `"NMR spectrum"`....the methyl groups, which arise from the `6H` of the methyl chain termini, and the `4H` of the methylene protons. The methyl protons are coupled to the 2 methylene protons, and so we should see a triplet. And given this coupling the methylene protons should appear as a quartet...i.e. the `2n+1` for simple first order spectra.

As always, integration helps us to differentiate the signals....the most intense peak arises from the most numerous protons...the six methyl protons....versus the 4 methylene protons...i.e. a `3:2` integration ratio

How many signals would you see in the `""^13C{""^1H}` `"NMR spectrum"`?

PS.

Please note for the better informed....yes I know that these protons are not magnetically equivalent...I am not going to open that can of worms here. You are welcome to do so, but this is probably a 2nd year question.

http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

The `""^1H` `NMR` spectrum of `"diethyl ketone"` was included at the kind suggestion and direction of Truong-Son N. ..many thx. The given spectrum does not include integration data, but we will have to bear that cross...