[jaydiaz21]

Do multiplets (like doublet of doublets) only happen when the compound is cyclic?

When do you have to multiply to get the correct number of peaks? For example you get 12 peaks for a Hydrogen signal between a CH2 (2+1=3) and a CH3 (3+1=4) so that 3x4=12. Do you always multiply when in between?

Thank you very much for the *delete me*

[discodermolide]

You get 3 signals for the CH₂ and 4 for the CH₃ giving a total of 7 signals!
Where did you get the multiplication from?

[Dan]

Do multiplets (like doublet of doublets) only happen when the compound is cyclic?

Why would it not occur in linear molecules?

When do you have to multiply to get the correct number of peaks? For example you get 12 peaks for a Hydrogen signal between a CH2 (2+1=3) and a CH3 (3+1=4) so that 3x4=12. Do you always multiply when in between?

So you mean a CH that is coupling to an adjacent CH₃ and an adjacent CH₂? This gives a triple quartet or quadrouple triplet (tq or qt) with 12 peaks. Yes, when calculating the number of peaks the splittings multiply - look up "NMR splitting tree diagram".

[Babcock_Hall]

@OP, How do you think that a doublet of doublets comes about?  A coupling tree might be helpful.