[earthnation112]

Question is:
1. Below is shown the ¹H NMR spectrum of (KBH₄). Explain the appearance of the spectrum. (spectra attached)

The answer given is:
Both ¹⁰B (I = 3, nat. ab. 20 %) & ¹¹B (I = 3/2, nat. ab. 80 %) NMR active and couple of ¹H. Hence 80 % of the sample contains ¹¹BH₄ which gives rise to a 1:1:1:1 ¹H NMR signal, whilst the remaining sample contains ¹⁰BH₄ which gives rise to a 1:1:1:1:1:1:1 septet signal. Overall integration of the two overlapping signals should be 4:1

Can someone help me understand how the answer is obtained, I know in this forum you don't answer questions, rather you try directing the enquirer towards the answer but here I have the answer but don't understand it!

So I know its a ¹H NMR spectrum, and I also know both ¹⁰B and ¹¹B are NMR active and I also know they abundance being 20% and 80%, where does l = 3 and 3/2 come from? I also know that since ¹¹B is more abundant the sample contains more of it than it does ¹⁰B. But why does this equate to ¹¹B giving rise to a 1:1:1:1 signal and the other gives rise to septet signal? Also why is the integration of the two 4:1?   

[mjc123]

I is the nuclear spin quantum number, you can find it in any textbook on the subject.
For a nucleus with spin 3/2, how many possible orientations are there of the spin vector relative to the magnetic field? What effect does this have on the nmr spectrum of a proton coupled to this nucleus?
Why is the integration 4:1? Oh come on...

[crawlingmcedge]

DIfferent spin comes from the isotopic weight with even/odd combinations of protons and neutrons having different spin types.

Also just slowly reread your abundance values and your relative integrations. The answer really is right in front of you.

[crawlingmcedge]

Why is the integration 4:1? Oh come on...

 

[earthnation112]

I is the nuclear spin quantum number, you can find it in any textbook on the subject.
For a nucleus with spin 3/2, how many possible orientations are there of the spin vector relative to the magnetic field? What effect does this have on the nmr spectrum of a proton coupled to this nucleus?
Why is the integration 4:1? Oh come on...

Thanks for the advice went back to my 1st year analytical notes and realized that a 3rd year student like myself shouldn't be having trouble with such basic questions!!!
Think it's because we don't have a module dedicated to analytical chemistry this year I had forgot everything!! The problem with memorising information just for exams and then dumping later!
Thanks