Question

Use the following coupling constant data to predict the ${}^{1}H$and the ${}^{19}F$spectra of the following:

$\begin{array}{ll}Species& J,\mathrm{Hz}\\ \left(\mathrm{a}\right)\mathrm{F}-\mathrm{C}\equiv \mathrm{C}-\mathrm{H}& 21\\ \left(b\right){\mathrm{CF}}_3-{\mathrm{CH}}_3& 12.8\\ \left(c\right){\left({\mathrm{CH}}_3\right)}_3-\mathrm{CF}& 20.4\end{array}$

Short answer

(a)

(b)

(c)

Step-by-step solution

Define spectra.

The hydrogen spectrum is a crucial piece of evidence for demonstrating an atom's quantized electronic structure. When an electric discharge is conducted across a gaseous hydrogen molecule, the hydrogen atoms in the molecule dissociate.

A spectrum is a graph or chart that depicts the intensity of light emitted over a range of energies.

Predict H1 and F19.

(a)

${}^1\mathrm{H}$has adjacent ${}^{19}\mathrm{F}$nucleus which is three bonds away.

So, ${}^1\mathrm{H}$signal splits into a doublet with a separation of $21$Hz.

Also, ${}^{19}\mathrm{F}$has neighboring ${}^1\mathrm{H}$such that ${}^{19}\mathrm{F}$will split into a doublet with a separation between line of $21\mathrm{Hz}$.

The ratio of peak intensities in each spectrum is $1:1$.

Predict H1 and F19.

(b)${}^1\mathrm{H}$has adjacent three ${}^{19}\mathrm{F}$nuclei which are three bonds away.

So,

${}^1\mathrm{H}$signal splits into a quartet with a separation of $12.8\mathrm{Hz}$between each peak. ${}^{19}\mathrm{F}$has neighboring three ${}^1\mathrm{H}$.

Therefore,

${}^{19}\mathrm{F}$will form a quartet with a distance between summits of$12.8\mathrm{Hz}$.

The ratio of peak intensities in each spectrum is $1:2:2:1$

Predict H1 and F19.

(c)

All nine ${}^1\mathrm{H}$are chemically equivalent.

Therefore, there will be 1 peak for all nine hydrogens such that those ${}^1\mathrm{H}$have adjacent ${}^{19}\mathrm{F}$nucleus.

So, ${}^1\mathrm{H}$signal splits into a doublet with a separation of $20.4\mathrm{Hz}$between each peak.

Also,${}^{19}\mathrm{F}$has neighboring $9^{1}H$,so ${}^{19}F$signal will split into 10 peaks with a separation between peaks of $20.4$Hz.

The ratio of peak intensities in the proton spectrum is localid="1646070365707" $1:1$and the areas of 10 peaks in the fluorine spectrum will be proportional to the expansion coefficients$\left(1+x\right)9$.