[ariaxxx]

How do you know if a reaction will be an oxymerc reduction or an acid catalyzed hydration? They both form the same products, so if you're asked to predict reagents how do you know which one?

For example my book says that for 1-methylcyclohexene to make 1-methylcyclohexanol the reagent is dilute H2SO4. But why can't it follow an oxymerc reaction too?

[zsinger]

Only use oxymercuration (somewhat dangerous) when you DO NOT DESIRE carbocation rearrangements.  Other than that, same product!
             -Zack

[orgopete]

An oxymercuration will also work. The difference is if rearrangement is not a competing reaction and you can easily add water, then you can just use acid. In this case the intermediate is a tertiary carbocation, so it would be easier to form. If you formed a secondary carbocation, the reaction will be slowed, stronger acid, and potential elimination occurring. With ethylene, you actually form a sulfate ester which must be hydrolyzed. In those cases, the oxymercuration reaction is better (OrgSyn prep).