[missUK11]

Hello All,

I have a question about the interpretation of the molecule in the attachment below. I understand that there are two protons in environment a and two protons in environment b and I worked out what the splitting pattern should be and I got a double doublet (dd) for both but apparently it is meant to be dddd for both. Am I correct? If not can someone please explain to me?

Thanks very much

[discodermolide]

Is it not a 3 bond coupling to proton C?

[missUK11]

No. It should be a 4 bond because c is in the meta position... am I  correct?

Is it not a 3 bond coupling to proton C?

[discodermolide]

sorry I was counting carbons. Yes a 4 bond.

[missUK11]

so would it be a double doublet or dddd?

sorry I was counting carbons. Yes a 4 bond.

[discodermolide]

A dddd.

[missUK11]

can you explain it to me please?

A dddd.

[discodermolide]

Draw your normal tree diagram for the coupling pattern.
See if you can fill in the coupling assignments.

[missUK11]

So you have to consider the couplings with protons b separately even though they are the same? And would it not be a ddd? How do you work out the overall splitting at the end...

Draw your normal tree diagram for the coupling pattern.
See if you can fill in the coupling assignments.

[discodermolide]

That diagram is for one of the protons only let's say a.
Just work out what is coupling to what, rinse and repeat for proton b
You can see the final pattern at the end, 8 lines 4 doublets predicted.

[missUK11]

So for proton a there would be coupling with proton b, proton c, and proton b again

and for proton b there would be coupling with proton with proton c, proton a and proton a

So this is should form three coupling constansts.

Is this correct 

That diagram is for one of the protons only let's say a.
Just work out what is coupling to what, rinse and repeat for proton b
You can see the final pattern at the end, 8 lines 4 doublets predicted.

[discodermolide]

The top proton a couples with b and c
therefore 3 coupling constants can be predicted. That's what the diagram shows.