The Addition of Borane to an Alkyne Hydroboration-Oxidation

What ketones would be formed from the acid-catalyzed hydration of 3-heptyne  

Which alkyne would be the best one to use for the synthesis of each of the following ketones  

Draw all the enol tautomers for each of the ketones in Problem 15. 

BH3 or R2BH (in THF) adds to alkynes in the same way it adds to alkenes. That is, boron is the electrophile and H is the nucleophile (Section 6.8). When the addition reaction is over, aqueous sodium hydroxide and hydrogen peroxide are added to the reaction mixture. The end result, as in the case of alkenes, is replacement of the boron by an OH group. The resulting enol immediately rearranges to a ketone. 

A carbonyl compound will be the product of hydroboration-oxidation only if a second molecule of BH3 or R2BH does not add to the ir-bond of the boron-substituted alkene. In the case of internal alkynes, the substituents on the boron-substituted alkene prevent the approach of the second boron-containing molecule. In the case of terminal alkynes, however, there is an H instead of a bulky alkyl group on the carbon that the second molecule adds to, so there is less steric hindrance toward the second addition reaction. Therefore, either BH3 or R2BH can be used with internal alkenes, but the more sterically hindered R2BH should be used with terminal alkynes. 

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