Q53E - Organic Chemistry (Mcmurry)

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)

Step-by-Step Solution

Answer

Step1: 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.

Step 2: 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.