For synthetic reactions where rearrangement, derivatization, or cyclization has occurred, a common task is to compare the NMR spectra between the starting material and the product. The similar peaks indicate a structural region where change has not occurred whereas the unique peaks indicate a region where change has occurred. Arguably, this becomes a peak mapping task as opposed to structure elucidation which is geared towards the unique pieces.
A cyclization reaction for the starting material, N-(2,6-dimethylphenyl)-N2,N2-dimethylalaninamide is shown below. The dotted circle represents the unknown region of the product. The CH3 groups circled in red indicate the similar regions between the starting material and the product.
The unknown product, N,N-dimethyl-1-(8-methyl-1,4-dihydro-2H-3,1-benzoxazin-2-yl)ethanamine, is shown below. The blue circle indicates the point of the cyclization and thus the area where an elucidator must piece together the experimental data to complete the structure.