Q12-43E - Organic Chemistry (Mcmurry)

Question

Question: Propose structures for compounds that meet the following descriptions:

       (a) An optically active compound $C_5{H}_{10}O$ with an IR absorption at $1730c{m}^{-1}$ .

       (b)  A non-optically active compound $C_5{H}_{9}N$  with an IR absorption at $2215c{m}^{-1}$

Step-by-Step Solution

Answer

(a)

                                                       
(b)

                                                

Step 1: IR spectroscopy

All the absorptions seen in alkanes is due to the C-C and C-H bonds. The C-H bonds show absorption in the region 2850 to $2950c{m}^{-1}$ and the C-C bonds are seen in the region 800 to$1300c{m}^{-1}$  .Most of the organic compounds exhibit these absorptions as they comprise saturated alkane portion.

Step 2: Proposing the structure of the compound with different description

(a)The optically active compound with the formula $C_5{H}_{10}O$that absorbs at $1730c{m}^{-1}$ can be given as:
                  

                           
                                                 Optically active compound

The IR absorption at this region is due to the saturated aldehyde. The name of the compound is 2-methylbutanal.

 

(b)The non optically active compound has a formula $C_5{H}_{9}N$  that absorbs at $2215c{m}^{-1}$ can be given as:

                                                 

                             
                                                  Non optically active compound
The absorption at this frequency is due to the cyanide functional group. The given compound is trimethylacetonitrile.