chem Nuc question

[Solstica]

---

Members do not see this ad.

When ranking the nuc and bases strength of SN1 & E2, is this the correct order?

(stronger) t-butO- > C2H5O- > CH3O- > OH- (weaker)

 

[TheRighteous]

I would think that the order is switched around:
OH- > CH3O- > CH3CH2O- > (CH3)3CO-

My reasoning is the effect of hyperconjugation. With a more substiuted R-group, your electron density on the oxygen is more spread out over the molecule as opposed to localized on the oxygen.

 

[Electrons]

I would think that the order is switched around:
OH- > CH3O- > CH3CH2O- > (CH3)3CO-

My reasoning is the effect of hyperconjugation. With a more substiuted R-group, your electron density on the oxygen is more spread out over the molecule as opposed to localized on the oxygen.

It sounds logical, but the pKa of t-butoxide is greater than ethoxide and the rest where OH- has the smaller pKa

 

[TheRighteous]

Mmh, so I guess hyperconjugation has nothing to do with it then.

Here's a link that has an indirect explanation:

http://books.google.com/books?id=1m...ts=nxZS-yz8q4&sig=OsvfqIgRbWDD5aLt7wQzHO1Lv1Q

Look to the middle of the page where it asks you to rank the alcohols based on acidity.

Methanol > Ethanol > 2-Propanol > t-Butanol

Since a strong acid's conjugate base is a weak base and a weak acid's conjugate base is a strong base, we can infer from the comparison that tert-butoxide is the strongest base as its conjugate acid is the weakest acid.

Therefore, based on basicity:
t-buxoide > ethoxide > methoxide > hydroxide

 

[TheWiredNerv]

When ranking the nuc and bases strength of SN1 & E2, is this the correct order?

(stronger) t-butO- > C2H5O- > CH3O- > OH- (weaker)

This is so for E2. I'm not quite sure t-butoxide would favor a SN1 reaction and would probably go E2 instead.