[AussieKenDoll]

I am studying F-19 NMR (I=1/2), of BF₃ , All 3 Fluorines couple to B-11 (I=3/2)  and gives a quartet of equal intensity of 1:1:1:1 rather than 1:2:2:1 according to pascal triangle. Why is that?

[Babcock_Hall]

You asked this before.  It might help to think about the difference between B-11 and the more commonly encountered spin 1/2 nuclei like C-13.  Does that help?

[AussieKenDoll]

Not really helpful! do you mean that B-11 has I=3/2 and C,H,F has I=1/2 , so what it has to do with not following the pascal triangle?

[Babcock_Hall]

You are on the right track.  Consider CDCl₃.  As you can tell from any C-13 spectrum taken in deuterated chloroform, the chloroform signal is a 1:1:1 triplet.  Now think about the properties of the deuterium nucleus.

[Babcock_Hall]

You could next try constructing a coupling tree for deuterated DMSO.  The H-1 spectrum shows a 1:2:3:2:1 pentet from a small amount of DMSO with the structure D₂HCS(O)CD₃.