Question

Treatment of compound C (molecular formula ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{8}}\mathbf{O}$) with ${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}\mathbf{MgBr}$, followed by H2O, affords compound D (molecular formula ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{14}}\mathbf{O}$). Compound D has a strong peak in its IR spectrum at 3600–3200 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. The ${\mathbf{H}}^{\mathbf{1}}$ NMR spectral data of C and D are given. What are the structures of C and D?Compound C signals at 1.3 (singlet, 6 H) and 2.4 (singlet, 2 H) ppm Compound D signals at 1.2 (singlet, 6 H), 1.6 (singlet, 1 H), 2.7 (singlet, 2 H), and 7.2 (multiplet, 5 H) ppm

Short answer

IR spectrum is a plot of the wavenumber of I radiation with percentage transmittance.

It is used to identify the functional groups present in a molecule because each group absorbs radiation of a different frequency.

There are 3 four regions in the IR spectrum of a molecule. Of these regions, the region of 4000-1000${\mathrm{cm}}^{-1}$ is called the functional group region and shows the peak of all functional groups in the molecule.

Therefore, the peaks in the functional group region areanalysedto determine the molecule's functional group.

Step-by-step solution

Analysis of IR spectrum

IR spectrum is a plot of the wavenumber of I radiation with percentage transmittance.

It is used to identify the functional groups present in a molecule because each group absorbs radiation of a different frequency.

There are 3 four regions in the IR spectrum of a molecule. Of these regions, the region of 4000-1000${\mathrm{cm}}^{-1}$ is called the functional group region and shows the peak of all functional groups in the molecule.

Therefore, the peaks in the functional group region areanalysedto determine the molecule's functional group.

Analysis of NMR spectrum

NMR spectroscopy is mainly of two types: ${}^1\mathrm{H}$ NMR spectroscopy and ${}^{13}\mathrm{C}$NMR spectroscopy.

These are used to categorize organic molecules. It gives the number of types of atoms under analysis.

The number of peaks in an ${}^1\mathrm{H}$ NMR spectrum gives the number of types of protons, and its area gives the number of protonsfor each type.

The number of protons adjacent to these protons is analysed using fine spectra.

 Step 3: Structure elucidation of C and D

The ${}^1\mathrm{H}$NMR spectrum of C has 2 peaks:

• Peak 1 at 1.3 ppm (${\mathrm{H}}_{\mathrm{a}}$protons)- It has 6 hydrogens. It is a singlet which means that it is attached to a tertiary carbon.
• Peak 2 at 2.4 ppm (${\mathrm{H}}_{\mathrm{b}}$protons)- It has 2 hydrogens. It is a singlet which means that it is attached to a tertiary carbon.

Since the IR spectrum does not show any peak, it is ether.

Therefore, the structure of compound C is:

Structure of C with labeled protons

Structure of D:

The ${}^1\mathrm{H}$NMR spectrum of D has 4 peaks:

• Peak 1 at 1.2 ppm (${\mathrm{H}}_{\mathrm{a}}$protons)- It has 6 hydrogens. It is a singlet, which means that it is attached to a tertiary carbon.
• Peak 2 at 1.6 ppm (${\mathrm{H}}_{\mathrm{b}}$protons)- It has 1 hydrogen. It is a singlet, which means that it is attached to a tertiary carbon.
• Peak 3 at 2.7 ppm (${\mathrm{H}}_{\mathrm{c}}$ protons)- It has 2 hydrogens. It is a singlet, which means that it is attached to a tertiary carbon.
• Peak 4 at 7.2 ppm (${\mathrm{H}}_{\mathrm{d}}$protons)- It has 5 hydrogens. It is the protons in the benzene ring.

Since the IR spectrum show peak at 3600-3200 ${\mathrm{cm}}^{-1}$, it is an alcohol.

Therefore, the structure of compound D is:

Structure of D with labeled protons