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Nmr splitting patterns help help help

so anyway nmr is doing my head in right now,

so say you have 2,3-dichlorobutane aand the question askes for the peaks intergration nd splitting patterns in proton nmr,

i understand that ther r 2 peaks because

the molecule is symmetrical so
ther are two hydrogen environments , the ch3's make one and the chcl's make the other

therefore i understand that th intgtn ratio is 6:2 or 3:1

now, with th spliiting patterns im stuck

i understand that th peak with itgrtn 6 (or 3) will have spliiting pattern of a doublet, cause the neighbouring carbon has 1 h and theres th n+1 rule

but th middle carbons surely threy have a quintet spliiting pattern or somethin cause say i take carbon 2 it is neighbouring a carbon with 3 hydrogens and also neighbouring a carbon with 1 hydrogen, which in total is 4 hydrogens ... so surely a quintet?

but markscheme says its a quartet :biggrin:

if any1 could explain pls

Reply 1

Yep

pllllllllllllllllllllllllllllleeaaaaseeeee someoneeeee anyooonnnnneeee :frown:

!!!

Reply 2

Kemics

Sorry not much help but it agree with you, should be a quintet?

Are you sure it's 2,3 dichlorobutane?

Reply 3

charco

Study Forum Helper

Original post by Yep

pllllllllllllllllllllllllllllleeaaaaseeeee someoneeeee anyooonnnnneeee :frown:

!!!

the two splits are different

Reply 4

Yep

Original post by charco

the two splits are different

meaning that for th second carbon one peak will be a quartet and the other a doublet? OMG IM AN IDIOT THANKS A BUNCH xD

Reply 5

Yep

Original post by Kemics

Sorry not much help but it agree with you, should be a quintet?

Are you sure it's 2,3 dichlorobutane?

100 % sure :smile:

i think u only look at 1 neighbouring carbon, not both

Reply 6

charco

Study Forum Helper

Original post by Yep

meaning that for th second carbon one peak will be a quartet and the other a doublet? OMG IM AN IDIOT THANKS A BUNCH xD

No, I'm sorry I didn't have a keyboard when I answered. What you get is a quartet of doublets, not a quintet.

i.e. each of the signals in the quartet is further split into a doublet. This is generally a mess, called a multiplet.

You potentially could also get a double quartet, but the reality is that the coupling constants are likely to be similar, or at least not large enough to resolve two quartets = messy signal (multiplet)

Reply 7

Yep

Original post by charco

okay im really confused, ;-; dumb it down a bit? :3

Reply 8

charco

Study Forum Helper

Original post by Yep

okay im really confused, ;-; dumb it down a bit? :3

If you look at the CHCl proton it is surrounded by CHCl (1 proton) on one side and CH3 (3 protons) on the other.

Each of these different environments splits the proton.

The coupling constant tells you by how much the signal is split. It is likely that the coupling constants from CH (on one side) and from CH3 (on the other) are different.

This gives rise to two possibilities:

1. A quartet (due to the neighbouring CH3) further split into two (from the CH)
2. A doublet (from the CH) each of which is split into a quartet(by the CH3)

It is likely that there is overlap between the split signals giving a mess (multiplet)