Question: A chiral hydrocarbon X exhibits a molecular ion at 82 in its massspectrum. The IR spectrum of X shows peaks at 3300, 3000–2850, and 2250 cm^-1. Propose a structure for X.

The IR spectrum allows for direct identification of the functional group. The IR spectrum allows the detection and identification of many organic functional groups because they show specific and characteristic absorption in the IR region.

The degree of unsaturation(DU) in the given molecule is calculated by using the formula:

$\mathbf{DU}\mathbf{=}({\mathbf{C}}_n\mathbf{+}\mathbf{1})\mathbf{-}\frac{{\mathbf{H}}_n}{2}\mathbf{-}\frac{{\mathbf{X}}_n}{2}\mathbf{+}\frac{{\mathbf{N}}_n}{2}$

The degree of unsaturation for the given molecule is: Thus the given molecule has either a triple bond or two rings.

role="math" localid="1649232230142" $\begin{array}{c}\mathrm{DU}=(6+1)-\frac{10}{2}\\ =7-5\\ =2\end{array}$

Chiral hydrocarbon with a molecular ion at m/z= 82

Molecular formula:${\text{C}}_{\text{6}}{\text{H}}_{\text{10}}$

IR absorptions at 3300 = Csp–H bond

3000–2850 ${\mathrm{cm}}^{-1}$ = C sp³–H bonds

2250 ${\mathrm{cm}}^{-1}$ = C=C bond

Structure of X