Q68E - Organic Chemistry (Mcmurry)

Question

Nitriles (RC≡N) react with Grignard reagents (R'MgBr). The reaction product from 2-methylpropanenitrile with methyl magnesium bromide has the following spectroscopic properties. Propose a structure.

MS: ${\mathbf{M}}^{\mathbf{+}}$ =86

 IR: 1715 ${\mathbf{cm}}^{\mathbf{-}}$

${}^{\mathbf{1}}\mathbf{H}$ NMR: 1.05 $\mathbf{\delta }$ (6 H, doublet, J 5 7 Hz); 2.12$\mathbf{\delta }$ (3 H, singlet); 2.67 $\mathit{\delta }$(1 H, septet, J 5 7 Hz) ${}^{\mathbf{13}}\mathbf{C}$  NMR: 18.2, 27.2, 41.6, 211.2 $\mathit{\delta }$

Step-by-Step Solution

Answer

Step 1: Mass spectra

It is a spectroscopy used to determine the molecular mass of the compound and the structure by plotting the ion signal as a function of mass to charge ratio.

Step 2: Identify compound from mass spectra

As per the given data, the molecular ion peak is present at 86 which means that the ketonic group is present in the molecule and by mas to charge ratio we can identify the molecular formula of the compound.

Step 3: Identify compound from NMR spectra

As per the given NMR data the peak is observed at the 1.05 due to the six proton of the 2 methyl which is adjacent in position at the terminal and a peak at 2.67 is observed by the CH surrounded by the 2 methyl group having 6 proton so show septet signals and at 2.12 peak is observed by the methyl proton at the terminal so it is sure from there that the nitrile group is replaced by the ketone and methyl.

Step 4: Identify compound from IR

As per the data the IR show absorption at 1715 ${\mathrm{cm}}^{-}$ that means the ketone group is present the reaction as followed   

Formation of carbonyl