Basicity or nucleophilic pathway?

[Electrons]

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What determines which route for the base to take if it can go either pathway (basic or nucleophilic)? Or it will always have both?

For example such as OH-, it can go either route. Is the answer to this depends on the substrate, LG, solvent, temperature, and orbital availability?

 

[Tina324]

can you post an example? =)

 

[Electrons]

3-bromobutane

CH3CH2CHBrCH3 + OH- -> CH3CH=CHCH3 (2-butene trans & cis as prod)
4 3 2 1

-OH can attack as nuc at the @2 position to do SN2 or acting as basic to attack @1 or @3 position to do the E2 right?

They didn't list any other solvent along with it. So does this mean the above could also have

CH3CH2CHOHCH3

as the answer?

 

[Electrons]

anyone?

 

[Tina324]

ok...I think yes it can be either SN2 or E2..n I think if it were to do E2 (liek the prob is saying..then it would probaby remove the H from carbon 1 because it is more easily accesible.

honestly though..i would think that SN2 would be the favored mechanism NOT e2...why is this e2 ppl?

I was under the impression that 1. strong base? then SN2 or E2...if substrate or nuc/base is bulky then E2 (or heat then E2)....

 

[glk2101]

since it is secondary substrate and you have a strong base, E2 is favored..
secondary substrates are not favored in sn2..
on the other hand, if you had a nucleophile like sulfur or a halide, then a substitution reaction could occur

 

[Tina324]

secondary aren't favored in E2 either...what do the other bases have to do with it? =/

 

[glk2101]

E2 can be favored for any substrate, primary, secondary, tertiary

and those aren't bases, theyre nucleophiles..thus they would give sn2.
goodluck

 

[Electrons]

I just checked against a few other books to dig down the answer for this. It turns out it can be both but favors E2 more. E2 would be the major product on secondary substrate with strong base. Glk2101 is right on that E2 is will work on pri, sec, or ter substrate. However, there will also be SN2 as minor product. So this problem is really asking for major product rather than the only product.