[Humr]

Hello, I am struggling with this rule and i would appreciate your advice. Teacher asked us what is the configuration on squalene alcohol when we get S acid after hydrolysis.

This rule says that carbonyl on acid part after esterification is in eclipse (i hope its correct word) position with largest group on alcohol part (red circle). So methyl has to come from from side with smallest group which is H. But that would mean H is in front when methyl is in front on S acid. This solution was not correct and teacher told us that squalene alcohol is S and OH group is in front.

In second case with menthol is it exactly like i was thinking for first time.

So where is the true ? Ii is really pissing me off that i don't see it.

Sorry, it should be in organic chemistry section, but i dont know how to delete topic.

[pgk]

Prelog’s and Cram’s rules concept is that the nucleophile attacks from the less hindered side.
If you draw your esterified squalene alcohol in chair conformation, you will see that the less hindered side is the one behind the hydrogens, regardless their small size.
You can also draw menthol benzoylformate in chair conformation and see what happens.
PS: Grignard reaction with ketones is faster than with esters. Thus, a smooth and equimolar Grignard attack to benzoylformate esters leads to the corresponding α-hydroxy-phenylacetate esters. But in practice, this does not always work like that and mixtures with tricarbinols, are obtained.