# NMR Coupling in an aromatic system via π system

I was presented today with the following molecule:

and asked the splitting pattern of $$\ce{H_a}$$ given that up to $$\mathrm{^3J}$$ and $$\mathrm{^4J}$$ coupling is allowed.

I thought that $$\ce{H_a}$$ couples to $$\ce{H_b}$$, $$\ce{H_c}$$ and $$\ce{H_d}$$ given that

• there is a $$\mathrm{^3J}$$ coupling to $$\ce{H_b}$$ (Clockwise)
• there is a $$\mathrm{^4J}$$ coupling to $$\ce{H_c}$$ (Clockwise)
• there is a $$\mathrm{^4J}$$ coupling to $$\ce{H_d}$$ (Anticlockwise)

Hence the splitting would be ddd.

However, the answer is apparently dd for the splitting of the $$\ce{H_a}$$ signal.

My thought was that anticlockwise, the $$\mathrm{^3J}$$ coupling is not possible due to the absence of a π bond in that direction down to $$\ce{H_d}$$ hence the coupling through the π system would not be possible.

Am I correct or is there another reason for no $$\mathrm{^3J}$$ coupling to $$\ce{H_d}$$?

• Please note that using MathJax in the title creates issues; \ce{…} should only be used for chemical compounds and reactions. Also, I added the compound name as image metadata (it's better to fill in something meaningful in place of "Enter image description here"), and I suggest you do the same in your future post as it makes finding your post much easier. Dec 29 '19 at 15:31
• @andselisk why does it create issues in the title? is mathJax not compatible with other browsers or other mobile devices? Dec 29 '19 at 15:35
• See here and there. Besides, in this case there is literally no justification for typing π with MathJax as it can be easily inserted as a Unicode character. Dec 29 '19 at 15:38