Unexplained peak cluster in proton NMR trace? I am working on a straight-forward NMR graph as part of my test prep. I have a pretty limited understanding of NMR, but I thoroughly read the chapter leading up to this practice question and am having difficulty explaining all of the peaks that I am seeing. Let me show the question and my understanding:

Here is the chemical and the trace that results.


My understanding of this problem is that there are four groups of equivalent hydrogens, and I numbered them 1-4. The 1st group has 3 equivalent hydrogens, with two adjacent non-equivalent hydrogens (group #2). Using the n+1 rule, the H group #1 should create 2+1=3 peaks in a cluster. Same goes for H group #4, since there are two adjacent hydrogens, so another 3 peaks. When considering H-group #2, the three hydrogens from H-group #1 should be 3+1=4 peaks. Same goes for H-group #3, which has the three hydrogens from H-group #4 so 3+1=4.

So, I am expecting to see 2 groups of 3 peaks and 2 groups of 4 peaks. I see the two groups of 4 peaks, but not the 2 groups of three peaks. Instead, I see 1 group of 6 peaks.

Am I supposed to believe that the 2 groups of 3 are just located so near it appears to be 6? Or am I missing something?

Thanks for any help!
You are correct. The chemical shift of methyl protons 1 and 4 are close to one another.  You still see the two expected triplets, they just have similar chemical shifts.  That's not too surprising since they are both methyl groups attached to a methylene group.  We could tell which triplet belongs to which methyl carbon by measuring and comparing the 2 sets of CH2-CH3 coupling constants.