[pulseultra]

Hey all,

I'm gonna try working backwards for this question, bare with me!

             

           
Now, I was wondering whether (nBu)Li (straight-chain-(nBu)Li) would be considered a bulky base in the abstraction of  a proton from the enolate below (I'll try attaching something)

                              Ar -CH₂ - CO^--(Bu)(OH)

                     
(I think I'm asking if we would observe regioselectivity?)

Thanks in advance,
Stef

[pulseultra]

Sorry, the post looks pretty bad, I'll make sure to preview it next time before posting. Again, sorry, I'm new at this.

[mschelthoff]

The best way to determine hindrance is to note the degree of substitution for the molecules involved. I'm sure you can deduce the degree of steric hindrance between primary, secondary and tertiary systems.

I'm also note really sure what molecules you're trying to illustrate there. I assume you're talking about n-Butyl lithium but I'm not sure what "(nBu)Li (straight-chain-(nBu)Li)" means.

[OC pro]

nBuLi is not a typical bulky base. It is a strong base.
Consider two points when deprotonate something: you have thermodynamic and kinetic control.
Thermodynamic means you will deprotonate this proton which will give the most stable anion (using non-bulky, strong bases).
Kinetic control is the case when one proton is more hindered to deprotonate than another one meaning the less hindered proton will be deprotonated first under kinetic conditions. To support kinetic conditions one uses sterically hindered (bulky) bases in combination with low temperature.
Therefore, nBuLi will give in most cases the thermodynamic product (anion).