May 29, 2012
Coupling patterns that overlap can be deceptively simple.
There are two possible coupling patterns for the CH2 signal at 3.39 ppm (top spectrum): a singlet or two ‘doublets’ (AB spin system) tilted towards each other. The bottom spectrum shows an example of two ‘doublets’ where the outer signals at 3.34 and 3.43 ppm are barely visible.
From the original problem set (top spectrum), the outer signals are not visible, as such, the coupling pattern is not clear. More information can be inferred from the structure. For example, if the CH2 protons are anisochronous, then they will exhibit different chemical shifts and thus rule out the singlet option.
Thank you TLP for you comment.