Question. The following spectra for A and B correspond to two structural isomers. The NMR singlet at1.16in spectrum A disappears when the sample is shaken with . The singlet at 0.6 ppm in the spectrum B disappears on shaking with . Propose structures for these isomers, and show how your structures correspond to the spectra. Show what cleavage is responsible for the base peak at 44 in the mass spectrum of A and the prominent peak at 58 in the mass spectrum of B.

From the mass spectrum of A, molecular ion peak is at 73, which is odd mass, means there must be odd number of nitrogens. If one nitrogen and no oxygen is present, then molecular formula is . Base peak is at 44 is, means this fragment must be present.

From IR spectrum, two peaks are observed around 3300 which indicates a primary amine so, structure 2 will not be correct for A.
From NMR spectrum, two exchangeable protons suggest amino group is present and multiplet at chemical shift value 2.8 means a, hence, structure of A must be structure 1.

Structure A determined from data given of spectrums

Compound B is an isomer of A, so its molecular formula must also be . IR spectrum shows only one peak at 3300 which indicates secondary amine. From NMR spectrum, we can infer that there is one exchangeable proton means, is present and also two ethyl groups are present.

Structure B determined from given data of spectrums