35b E - Organic Chemistry (Mcmurry)

Question

Question: At what approximate positions might the following compounds show

IR absorptions?

(b) 

Step-by-Step Solution

Answer

(b) It shows two distinguished absorption due to alkyne $\left(C\equiv C\right)$at 2100-2600 $c{m}^{-1}$$\left(C\equiv C-H\right)$ and at 3300$c{m}^{-1}$.

Step-by-step Solution Step 1:IR absorption

In general, IR absorption is caused by the interaction between the IR electric field vector and molecular dipole transition related to the molecular vibrations. Absorption is at maximum when the electric field vector and dipole transition moment are parallel to each other.

Step 2: Identify the functional group

Functional groups are groups of one or more atoms with distinctive chemical properties regardless of what is attached to them.

The atoms of the functional group are bound by covalent bonds with one another and with rest of the molecule.

Compound (b) doesnot contain any functional group.

Step 3: Position at which compound show IR absorptions

Given compound

(b) It shows two distinguished absorptions due to alkyne $\left(C\equiv C\right)$at 2100-2600 $c{m}^{-1}$and$\left(C\equiv C-H\right)$ at 3300 $c{m}^{-1}$.