The relation between the activation energies | vedclass

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(D) The hydrogenation of benzene to cyclohexane occurs in three steps. $1$. The first step involves the addition of $H_2$ to benzene to form $1,3-$cyc

Vedclass · Accepted Answer

$E_1 > E_3 > E_2$

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(D) The hydrogenation of benzene to cyclohexane occurs in three steps. $1$. The first step involves the addition of $H_2$ to benzene to form $1,3-$cyclohexadiene. This step requires the loss of the aromatic resonance energy of benzene,which is a very high energy barrier. Thus,$E_1$ is the highest activation energy. $2$. The subsequent steps involve the hydrogenation of cyclohexadiene to cyclohexene $(E_2)$ and then to cyclohexane $(E_3)$. These steps involve the hydrogenation of isolated double bonds,which have much lower activation energies compared to the destruction of aromaticity. $3$. Since the first step is the rate-determining step due to the loss of aromaticity,$E_1$ is significantly larger than $E_2$ and $E_3$. $4$. Comparing $E_2$ and $E_3$,the hydrogenation of the conjugated diene system in cyclohexadiene $(E_2)$ is generally faster than the hydrogenation of the isolated double bond in cyclohexene $(E_3)$,meaning $E_2 Therefore,the correct order is $E_1 > E_3 > E_2$.

The relation between the activation energies $(E_1, E_2, E_3)$ of the following reactions is:

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