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I know that the $\ce{Si-Cl}$ bond has a slightly higher energy, but silyl chlorides are much more readily hydrolyzed compared to alkyl chlorides. I do not fully understand why that is. My thoughts so far are:

  • There is a better match in energy between the orbitals of the $\ce{Si-Cl}$ bond and water.

  • Reactions proceed when there is a favorable interaction between HOMO and LUMO.

  • In this case, the HOMO is the lone pair on the water molecule. The LUMO of a $\ce{Si-Cl}$ bond is closer to it in energy compared to a $\ce{C-Cl}$ bond.

Is this the right argument to take?

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Using $\ce{CCl4}$ and $\ce{SiCl4}$ as the basis for comparison, there are several reasons.

  1. The greater electronegativity difference between Si and Cl leads to a larger $\delta^+$ on silicon, making it more electrophilic and susceptible to attack by water.

  2. Larger size of Si means that there is less steric hindrance towards the approach of water.

  3. It is possible that the hydrolysis of $\ce{SiCl4}$ proceeds via an alternative, faster pathway that involves a five-coordinate intermediate (as opposed to $\ce{CCl4}$, in which five-coordinate carbon does not occur).

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