Q.57. - Organic Chemistry

Question

Question: Thymol (molecular formula ${\mathit{C}}_{\mathbf{10}}{\mathit{H}}_{\mathbf{14}}\mathit{O}$ ) is the major component of the oil of thyme. Thymol shows IR absorptions at 3500–3200, 3150–2850, 1621, and 1585 $\mathit{c}{\mathit{m}}^{\mathbf{-}\mathbf{1}}$ . The  ${}^{\mathbf{1}}\mathit{H}$ NMR spectrum of thymol is given below. Propose a possible structure for thymol.

Step-by-Step Solution

Answer

Answer

Step 1: Signals in H 1 NMR spectrum

Each hydrogen atom present in a compound gives a characteristic signal in the ${}^{\mathbf{1}}\mathit{H}$  NMR spectrum.

The splitting pattern of peaks in ${}^{1}H$ NMR spectrum is predicted using the n+1 rule where n represents the number of hydrogens on the carbon adjacent to the carbon atom which contains the hydrogen under consideration.

Step 2: Analyzing the given IR data

The IR peak at $3500-3200 c{m}^{-1}$  corresponds to OH functional group.

IR peak at  $3150-2850 c{m}^{-1}$ corresponds to $s{p}^2$ and  $s{p}^3$ C-H stretching.

The peak at $1621 c{m}^{-1}$ corresponds to  $C=C$ stretch.

The inference from the given data is that the compound consists of  $s{p}^2$ and  $s{p}^3$ hybridized carbon atoms and an OH group.

Step 3: Analyzing the given H 1 NMR spectrum

The peaks at 6-8 ppm indicate aromatic protons.

The peaks at 6-8 ppm correspond to three hydrogen atoms which indicate that the benzene ring consists of three non-equivalent hydrogen atoms.

The multiplet at 3.3 ppm indicates that the carbon adjacent to the concerned proton consists of six hydrogen atoms (such that 6+1=7).

Doublet at 1.2 ppm corresponding to six hydrogensindicates that the carbon atom adjacent to six equivalent hydrogens contains one hydrogen (1+1=2).

Therefore, the structure of thymol (according to the given spectrum) is:.

           Thymol