Q26P - Organic Chemistry (Mcmurry)

Question

Describe the prominent IR absorptions and mass spectral peaks you would expect for the following compound:

Step-by-Step Solution

Answer

Step 1:Infrared and mass spectroscopy

Infrared and mass spectroscopy are two important tools for a chemist to examine molecular compound.

 

Spectroscopy is the “lens of a forensic investigation” as they detect the chemical compound by molecular analysis.

Step 2: Infrared absorption for 2-isobutylcyclopentanone

The given compound is 2-isobutylcyclopentanone.

 

2-isobutylcyclopentanone has the 5-membered ring, thus giving the only IR absorption at 1750${\text{cm}}^{\text{-1}}$.

 

2-isobutylcyclopentanone shows mass spectra as follows:

• The product of alpha cleavage, which occurs at the ring having the same mass as the molecular ion, gives the peak at m/z = 140
• The charged fragment result from Mc Lafferty rearrangement gives the peak at m/z = 84.

 

The m/z value due to alpha cleavage and Mc Lafferty rearrangement is shown below.

2-isobutylcyclopentanone m/z values