[ASU]

This is homework that is due, and I was hoping someone might be able to look over it and maybe provide some suggestions.  Sorry that the pencil showed up really light and it's kind of messy.

I was particularly wondering if the carbocation + sign on the mechanism needs to be put in the exact spot the substituent is added.  For instance, in the first mechanism, the Cl.



URL if image doesn't show up: http://img260.imageshack.us/my.php?image=scan0002gj5.jpg

[macman104]

Yes, it does.  But it looks good, and very clean drawings, nice job!

[ASU]

So say for the second mechanism, should I draw the first intermediate before the hydride shift so that the hydrogen off the cyclohexane is going around and under methyl group and to the carbocation?

[macman104]

I don't understand your question please explain what you mean for your second mechanism.  Can you draw what you mean, and then we can just compare the two ways you think you should draw it?

[azmanam]

I think I know what you're asking.  Because there's free rotation about the carbon-carbon bond connecting the carbocation to the cyclohexyl group, the hydride has an equal opportunity to transfer to the top or bottom face of the carbocation.  The newly formed stereocenter containing the methyl group will be formed in a racemic mixture.