1HMR confusion?

[nothingsus]

So I was doing some checkpoint questions and I ran across a question regarding the 1nmr spectrum of this

CH(Cl)(Cl)CH(Cl)CH3

The book says that the central carbon has a peak with 8 splits (octet?). Why is this? It only has 4 neighbouring protons.

[Alwin]

So I was doing some checkpoint questions and I ran across a question regarding the 1nmr spectrum of this

CH(Cl)(Cl)CH(Cl)CH3

The book says that the central carbon has a peak with 8 splits (octet?). Why is this? It only has 4 neighbouring protons.

Hmm, this one looks like a question I answered on AN previously, was it from checkpoints I think?


(1,1,2-Trichloropropane)

Okay, so firstly, its not technically called an octet, rather a multiplet. What happens is the splitting is 'double spilt'. Sorry if I'm not using the correct terminology but I'm just trying to explain it to you as simply as possible.

So I'm assuming that you got Peak B is the middle (see above picture or the one in checkpoints) carbon, yeah? Now on one neighbouring carbon there are 3H which would give a quartet. BUT on the other carbon there is 1H in a different bonding environment which should give a doublet. What happens is since the hydrogens in the 2 neighbouring carbons are different, they split each other's splitting

The peak B becomes a doublet of quartets (or equally a quartet of doublets). since 2 x 4 = 8, the resultant is a multiplet which appears as an octet.

Hopefully this makes sense to you However, I have never seen a multiplet on a vcaa exam, nor do I believe that its in the study design

EDIT: The original thread was here: Checkpoints H1 NMR Spectroscopy Q 26 c  HELP!

[nothingsus]

Thanks for the answer! I guess it's sort of out of the scope of the study design, but still nice to know.