Question about alcohol nomenclature

Question

The question is: 3-methyl-2-butene is reacted with HBR2 to form an organoborane which is subsequently reacted with aqueous basic hydrogen peroxide. What are the products? Is the product solution optically active?

The answer is supposedly: The product is a racemic, optically inactive mixture of (2R)- and (2S)-3-methyl-2-butanol ((2R)- and (2S)-2-hydroxy-2-methylbutane).

I think can see how 3-methyl-2-butanol is produced. The formula for that is CH3CH(OH)CH(CH3)CH3. From the placement of the brackets, I assume what the author is doing is giving an alternative naming that doesn't follow IUPAC priority because in the book I am reading, alcohols haven't been introduced yet. I think I am unclear about the naming mechanism though, because I would think that the formula for 2-hydroxy-2-methylbutane would be CH3C(OH)(CH3)CH2CH3 (both the OH and CH3 being attached to C-2.) Am I misreading the formula, or is this possibly a typo?

Answer 1

It's not a typo, it's a quirk of the naming rules, and an error in naming the starting material, not the product.  In naming, although there is some flexibility, you use the lowest numbers possible.  In the starting material, carbons 2 and 3 of the butyl chain are equivalent.  So it could have, and perhaps should have, been named 2-methyl-2-butene.  That's the same compound drawn the other way around.  In the products, you can end up with the hydroxyl on the adjacent carbon, in which case you have substituents on carbons 2 and 3.  So is it 3-methyl-2 butanol or 2-methyl-3-butanol?   The hydroxyl takes priority so it's the first.  But when the hydroxyl ends up on the same carbon, they are both the same, either 2,2 or 3,3.  You choose the lowest number, 2.    

Molecules are often being 'flipped' like this in the course of reactions as their structure changes, you have to get used to rotating them in your head.