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Oxidation using chromium trioxide

Oxidation of alcohol with $\ce{CrO3}$

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I have come across different kinds of oxidation using ester formation (eg. Selenium/Osmium ester).This mechanism deals with the chromate ester. The structure of $\ce{CrO3}$ seems rather confusing to me:

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I found claims that $\ce{Cr}$ atom has any one out of the following hybridisation.

  1. $\ce{sp^2}$ (claimed by an instructor)
  2. $\ce{d^2s}$ (claimed by a student on different forum)
  3. $\ce{pd^2}$ (claimed by me)

I do not know which is correct description, but post computational analysis, I can be pretty confident for the 3rd.

My questions are as follows:

  1. What is the correct (nearly) hybridisation (if it exists)?
  2. Geometry of the mechanism (i.e. approach of electrons in a 3D model, can be provided as a thought as well)
  3. Why isn’t the five membered ring completed with $\ce{OH}$ instead of pi bonded Oxygen.

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