Can someone please explain why the CH2 peaks here are singlet not triplet? Thanks
For R, the CH2 groups are an equivalent environment, so despite being bonded directly to each other, they don’t split each other. Splitting only occurs when two non-equivalent environments are bound to each other.
For example, in CH3CH2CH2OH, the CH2 groups are non-equivalent, as one is bound to a CH3 whereas the other is bound to an OH, so they are not the same environment and they affect the splitting of their respective signals. However, in CH3CH2CH2CH3, both CH2 groups would be equivalent, so they would both split the signal they cause into a quartet.