Nonequivalent Methylenes in Certain Ether Systems

A series of ethers of the form R1R2R3COCH2R (where R1≠R2≠R3≠ R1 and R can be the same as R1 or different) were prepared. The ether methylenes (underlined) were analyzed by NMR spectroscopy and found to be magnetically non-equivalent (i.e. chemical shift between methylenes Δv ≠ 0) in some cases. A semi-quantitative correlation between Δv and the steric size of R1,R2,R3, and R was observed suggesting restricted rotation around the C-O bond as the cause of the observed magnetically non-equivalent methylene protons.