Question

Propose a structure consistent with the following spectral data for a ${\mathbf{C}}_{\mathbf{8}}{\mathbf{H}}_{\mathbf{18}}{\mathbf{O}}_{\mathbf{2}}$compound :

IR: $\mathbf{3350}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$${}^{\mathbf{1}}\mathbf{H}$NMR: $\mathbf{1}\mathbf{.}\mathbf{24}\mathbf{\delta }$ (12 H, singlet); $\mathbf{1}\mathbf{.}\mathbf{56}\mathbf{\delta }$(4 H, singlet); $\mathbf{1}\mathbf{.}\mathbf{95}\mathbf{\delta }$(2 H, singlet)

Short answer

Alcohols comprise a strong C-O absorption peak near$\mathbf{1050}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. A characteristic O-H stretching absorption is also seen in the range of 3300 to$\mathbf{3600}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. The position of O-H stretch depends on the hydrogen bonding in that particular molecule.

Step-by-step solution

IR and NMR spectrum of alcohols

Alcohols comprise a strong C-O absorption peak near$\mathbf{1050}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. A characteristic O-H stretching absorption is also seen in the range of 3300 to$\mathbf{3600}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. The position of O-H stretch depends on the hydrogen bonding in that particular molecule.

Proposing the structure of the compound from the NMR spectrum

The degree of unsaturation for the compound ${\mathrm{C}}_8{\mathrm{H}}_{18}{\mathrm{O}}_2$can be given as:

$$\begin{gathered} \mathrm{Degree}\mathrm{of}\mathrm{unsaturation}=\frac{2\mathrm{C}+2+\mathrm{N}-\mathrm{H}-\mathrm{X}}{2} \\ =\frac{2\times 8+2+0-18-0}{2} \\ =\frac{18-18}{2} \\ =0 \end{gathered}$$

The compound has zero degree of unsaturation. Hence it has no double bonds or rings.

The IR band at$3350{\mathrm{cm}}^{-1}$ indicates the presence of a hydroxyl group. The compound is symmetrical and has a simple NMR. The compound has four methyl groups connected to the carbon with no hydrogen on it. The compound also has two oxygen atoms. The two proton singlet$1.95\mathrm{\delta }$ at can be assigned to two OH groups. The compound is a diol and the structure can be given as:

Structure of the compound

Hence, the name of the compound is 2,5-Dimethyl-2,5-hexanediol.