H3C-CH2-CHBr2
How many peaks will the proton in CH2 be split? The answer is 8 but I only counted 5 splits. 3 from the methyl and 1 from the CHBr2 and + 1 from the n+1 rule. I don't understand where 8 came from.
How many peaks will the proton in CH2 be split? The answer is 8 but I only counted 5 splits. 3 from the methyl and 1 from the CHBr2 and + 1 from the n+1 rule. I don't understand where 8 came from.
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Well, you're not taking complex splitting into account. H NMR can be tricky because, in this case, the CH2 would be split into a quartet by the CH3, via the n+1 rule. However, the CHBr2 would also cause each of those quartet peaks to split again, forming eight peaks. If you're actually looking at the NMR, you may not really see eight peaks because sometimes low resolution can cause the peaks to wash out.
Essentially, you need to realize that the n+1 rule applys only to neighboring carbons that are identical. Here the CH3 and CHBr2 are not the same, so each peak is split by the n+1 rule of the other neighbor.
Ex.
The CH3 forms a quartet: llll
The CHBr2 would double that (apply n+1 again): llll llll
Total of eight peaks.
Hope this helps.
Essentially, you need to realize that the n+1 rule applys only to neighboring carbons that are identical. Here the CH3 and CHBr2 are not the same, so each peak is split by the n+1 rule of the other neighbor.
Ex.
The CH3 forms a quartet: llll
The CHBr2 would double that (apply n+1 again): llll llll
Total of eight peaks.
Hope this helps.