[namesis]

How is the Carbon hybridized during the transition state of the reaction between the hydroxide ion and methyl iodide?

[Babcock_Hall]

It is a forum rule that you must show your attempt before we can help you.  A good place to start might be to identify the mechanism.

[namesis]

It is a forum rule that you must show your attempt before we can help you.  A good place to start might be to identify the mechanism.

Thank you! I think that according to the mechanism, the molecule will start changing shape to go from sp3 to an "inverted" sp3. So on the way, something like an umbrella getting inverted from the wind will happen. Therefore, something between sp3 and sp2 while p orbital is momentarily getting back to its initial state in the middle.

[Babcock_Hall]

The hybridization of the carbon atom in the transition state seems to resemble sp² hybridization.  However, I have yet to find a good textbook treatment, other than Jackson's:  https://books.google.com/books?id=AjEz6uC8NSkC&pg=PA63&lpg=PA63&dq=Sn2+reaction+hybridization&source=bl&ots=VqeblYkIKJ&sig=OjK2s1DF_FY0Jgp7zAHUxH2ENfA&hl=en&sa=X&ved=0ahUKEwjb4u6k9YjKAhWISiYKHd0mCn84ChDoAQgbMAA#v=onepage&q=Sn2%20reaction%20hybridization&f=false

[Irlanur]

Since the hybridisation is determined by the geometry and we usually think about Sn2 as a pentacoordinated transition state, sp2 makes perfect sense.