how to tell if substitution or elimination rxn will dominate?

Question

organic chem question????????????????

more eg. on good Nucleophiles (that promotes E1/E2) and strong base pls ?!

Answer 1

It is a little more complicated than the answers so far given.

Substitution will predominate with primary and some secondary carbons with any nucleophiles, because the SN2 reaction is readily available, if the electrophilic carbon has a good leaving group. However, the nature of the nucleophile matters. For example, tert-butoxide is a hindered nucleophile, so it will tend to favor elimination reactions and, in most cases, do nothing with primary carbons.

Elimination is favored for tertiary and many secondary carbons, when there is a strong base. The steric hinderance prevents the necessary backside attack of an SN2 with these carbon atoms and so elimination predominates, via an E2

If the nucleophile is not very basic and you have a secondary or tertiary carbon, you get a mixture of products, depending on reaction conditions, from an SN1 and E1

Answer 2

It will depend on whether the reactant is a stronger nucleophile or base. Strong bases such as hydroxide or ethoxide, etc. will tend to result in elimination reactions. Reactants with higher nucleophillic character such as cyanide or chloride will tend to result in substitution reactions.

Answer 3

I thought substitution products were always dominate. Maybe not.... look to see if the product is primary, secondary, or tertiary? Goodness I wish I had my notes in front of me.