The nine peaks seen here is very common for this type of substance. Essentially you use 6 and 2 so the n+1 rule suggests 9 peaks. However they are non equivalent so this cannot apply. Instead your coupling constants (J, Hz) are such that you have overlapping peaks so you have a "pseudo nonuplet" made up of a triplet of sextets which overlap. when peaks overlap the intensity increases proportionately (see doublet of doublets which overlaps to form an apparent triplet). This is, however, a multiplet and should be reported as such, it should not be reported as a nonuplet (spelling may be wrong)
Draw your Pascals triangle and work out the relative peak heights for your three sextets in excel (or similar) and then overlap them so you get 9 peaks. The heights should match what you have.
I made a great many of these isobutyl type compounds during my PhD, I just assumed the n+1 rule applied and accepted 9 peaks. Credit to you for questioning it, I didn't and someone made me look a fool during a presentation by asking the same question you have raised.
ChemBuddy | 
Chem Reddit | 
Topic: 1H NMR Help (Read 3497 times)