Question

How could you distinguish the 1 H NMR spectra of the following compounds?

Short answer

A)

Structure with chemical shift values

B)

Structure with chemical shift values

C)

Structure with chemical shift values

Step-by-step solution

Step-by-Step Solution Step 1: NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy gives information about the structure of the molecule by observing the bonding of carbon and hydrogen atoms.

The characteristics of ${}^1\mathbf{H}$NMR spectrum are shown below:

• Number of signals (chemically non-equivalent)
• Position of signals (chemical shift)
• Shape of the signals (Integration and splitting of peaks).

The chemical  shift values for the following compounds

a)

The structure of the compound A is as follows:

${\mathrm{H}}_3\mathrm{C}-\mathrm{O}-{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_3$

Dimethoxy methane

Dimethoxy methane has two non-equivalent protons. They are methyl protons $\left({\mathrm{CH}}_3\right)$and methylene proton $\left({\mathrm{CH}}_2\right)$. So, dimethoxy methane gives two signals.

Methyl protons absorb at 3.30$\mathrm{\delta }$(singlet) and methylene protons absorb at 4.50$\mathrm{\delta }$(singlet) in ${}^1\mathrm{H}$NMR spectrum.

The structure with chemical shift values is as follows:

Structure with chemical shift values

b)

The structure of the compound B is as follows:

${\mathrm{H}}_3\mathrm{C}-\mathrm{O}-{\mathrm{CH}}_3$

methoxymethane

The compound methoxymethane has one non-equivalent proton (methyl proton). So, methoxymethane gives one signal. Methyl protons absorb at 3.30$\mathrm{\delta }$ (singlet) in ${}^1\mathrm{H}$NMR spectrum.

The structure with chemical shift values is as follows:

Structure with chemical shift values

c)

The structure of the compound C is as follows:

1,3-dimethoxy-2,2-dimethylpropane

The compound 1,3-dimethoxy-2,2-dimethylpropane has three non-equivalent protons. They are two methyl protons and one methylene proton. So, 1,3-dimethoxy-2,2-dimethylpropane gives three signals in the ${}^1\mathrm{H}$NMR spectrum.

One methyl proton absorbs at 3.30$\mathrm{\delta }$(singlet) in${}^1\mathrm{H}$NMR spectrum, this is because it is attached to the oxygen atom.

The other methyl proton absorbs at 0.99$\mathrm{\delta }$(singlet) and the methylene protons absorb at 3.79$\mathrm{\delta }$(singlet) in${}^1\mathrm{H}$NMR spectrum.

The structure with chemical shift values is as follows:

Structure with chemical shift values