Orgo 2: addition of Nuc hydride ion

[nancy9494]

hello,

 I wanted to know if i labeled the possible products correctly [i.e. minor vs. major].

 

reasoning: Although there is less steric hinderance for the Hydride ion through front (because of sterics of the CH(CH3)2 group on the dash) that won't be deciding factor for the amount of major product formed. The back side attack will form the major product because the larger OH and CH(CH3)2 groups are anti to each other. Is this correct?

thank you in advance 

[hypervalent_iodine]

You’re reasoning is sound, but I think you need to look again at how you e drawn the products. If the major product is the one where the hydride attacks on the opposit face to the alkyl group, then why have you drawn it on the same face in your major product?

[nancy9494]

I'm confused. Shouldn't the larger substituents be opposite to each other? So the OH has to be oriented away from the CH(CH3)2. Did I label them incorrectly then? If so, is it because the strong nucleophile of Hydride anion is irreversible so the path of least resistance [front side attack] will determine the major product formed? 

 

[hypervalent_iodine]

Apologies, I didn’t read your reasoning thoroughly. It would depend on the conditions, probably. You are right that the OH being orientated away from the alkyl group would be more thermally stable. Kinetic stability would favour hydride attack on the least hindered side, however. I believe the kinetic product will be favoured in this case. You should look up Cram’s rule. It explains the concepts in more detail. 

[nancy9494]

as always thanks again!