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Why is cyclopropane more acidic than propane
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Mike Jones
Why is cyclopropane more acidic than propane
Indeed, according to the Evans $\mathrm{p}K_\mathrm{a}$ table the cyclopropane $\ce{C-H}$ bond $(\mathrm{p}K_\mathrm{a} \approx 46)$ is more acidic than the $\ce{C-H}$ bond on the central carbon in propane $(\mathrm{p}K_\mathrm{a} \approx 51)$.
We know that, in general, the acidity of $\ce{C-H}$ bonds follows the order $\mathrm{sp \gt sp^2 \gt sp^3}$. This is because the more $\mathrm{s}$-character in an orbital, the more stable (lower energy) electrons are in the orbital.
The $\ce{C-H}$ bonds around the central carbon in propane are close to being $\mathrm{sp^3}$ hybridized, whereas the $\ce{C-H}$ bonds in cyclopropane are roughly $\mathrm{sp^{2.46}}$ (see this earlier answer to see how the hybridization in cyclopropane was determined).
Now, when we compare the hybridization of the $\ce{C-H}$ bonds in cyclopropane and propane we see that there is more s character in the cyclopropane $\ce{C-H}$ bonds, this explains the increased acidity.
Indeed, according to the Evans $\mathrm{p}K_\mathrm{a}$ table the cyclopropane $\ce{C-H}$ bond $(\mathrm{p}K_\mathrm{a} \approx 46)$ is more acidic than the $\ce{C-H}$ bond on the central carbon in propane $(\mathrm{p}K_\mathrm{a} \approx 51)$.
We know that, in general, the acidity of $\ce{C-H}$ bonds follows the order $\mathrm{sp \gt sp^2 \gt sp^3}$. This is because the more $\mathrm{s}$-character in an orbital, the more stable (lower energy) electrons are in the orbital.
The $\ce{C-H}$ bonds around the central carbon in propane are close to being $\mathrm{sp^3}$ hybridized, whereas the $\ce{C-H}$ bonds in cyclopropane are roughly $\mathrm{sp^{2.46}}$ (see this earlier answer to see how the hybridization in cyclopropane was determined).
Now, when we compare the hybridization of the $\ce{C-H}$ bonds in cyclopropane and propane we see that there is more s character in the cyclopropane $\ce{C-H}$ bonds, this explains the increased acidity.
Indeed, according to the Evans $\mathrm{p}K_\mathrm{a}$ table the cyclopropane $\ce{C-H}$ bond $(\mathrm{p}K_\mathrm{a} \approx 46)$ is more acidic than the $\ce{C-H}$ bond on the central carbon in propane $(\mathrm{p}K_\mathrm{a} \approx 51)$.
We know that, in general, the acidity of $\ce{C-H}$ bonds follows the order $\mathrm{sp \gt sp^2 \gt sp^3}$. This is because the more $\mathrm{s}$-character in an orbital, the more stable (lower energy) electrons are in the orbital.
The $\ce{C-H}$ bonds around the central carbon in propane are close to being $\mathrm{sp^3}$ hybridized, whereas the $\ce{C-H}$ bonds in cyclopropane are roughly $\mathrm{sp^{2.46}}$ (see this earlier answer to see how the hybridization in cyclopropane was determined).
Now, when we compare the hybridization of the $\ce{C-H}$ bonds in cyclopropane and propane we see that there is more s character in the cyclopropane $\ce{C-H}$ bonds, this explains the increased acidity.
Indeed, according to the Evans $\mathrm{p}K_\mathrm{a}$ table the cyclopropane $\ce{C-H}$ bond $(\mathrm{p}K_\mathrm{a} \approx 46)$ is more acidic than the $\ce{C-H}$ bond on the central carbon in propane $(\mathrm{p}K_\mathrm{a} \approx 51)$.
We know that, in general, the acidity of $\ce{C-H}$ bonds follows the order $\mathrm{sp \gt sp^2 \gt sp^3}$. This is because the more $\mathrm{s}$-character in an orbital, the more stable (lower energy) electrons are in the orbital.
The $\ce{C-H}$ bonds around the central carbon in propane are close to being $\mathrm{sp^3}$ hybridized, whereas the $\ce{C-H}$ bonds in cyclopropane are roughly $\mathrm{sp^{2.46}}$ (see this earlier answer to see how the hybridization in cyclopropane was determined).
Now, when we compare the hybridization of the $\ce{C-H}$ bonds in cyclopropane and propane we see that there is more s character in the cyclopropane $\ce{C-H}$ bonds, this explains the increased acidity.
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