[mana]

hi
I can't understand when an alkyl halide participate in nucleophilic substituion reaction and when in elimination reaction, I know the steric effect and heat are suitable for elimination reaction but for example in the reactions below both products are possible
the hindrated base can facilitate elimination reaction, does it mean that NaOEt just react as nucleophile instead of base?

[Babcock_Hall]

The last sentence you wrote looks backwards with respect to the words nucleophile and base.  I don't know what the word "hindrated" means.  Do you mean hindered?  How hindered is sodium ethoxide, in your opinion?

A number of compounds are both strong bases and strong nucleophiles.  Which reaction predominates depends on the solvent, the degree of substitution of the alkyl halide, temperature, and probably other things I am not thinking of at the moment.

[mana]

The last sentence you wrote looks backwards with respect to the words nucleophile and base.  I don't know what the word "hindrated" means.  Do you mean hindered?  How hindered is sodium ethoxide, in your opinion?

sorry for my poor English I mean big bases such as tert butoxide compared with ethoxide, but the problem is that tertiary alkyl halide can participate in E2 also in SN1 and SN2 so it is very confusing

[Babcock_Hall]

My best guess is that secondary and tertiary alkyl halides will eliminate in the presence of a strong base, whereas primary alkyl halides will substitute.  Tertiary butoxide is a good example of a strong base but a poor nucleophile.  Can you think of examples of compounds that are strong nucleophiles but not strong bases?  Secondary alkyl halides can also substitute, depending on the identity of the nucleophile/base and on the solvent.