GRE Subject Test: Chemistry : Elimination Reactions

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

Example Question #1 : Elimination Reactions

Which of the following would be the best base to perform an E2 elimination?

Possible Answers:

Potassium hydroxide


Sodium butoxide


Sodium cyanide

Correct answer:

Sodium butoxide


The correct answer is sodium butoxide. Remember from your studies that for E2 reactions to be highly preferred they require a "big, bulky, base".

First eliminate ammonium  for it is not a base and is the conjugate acid form of ammonia. Then we can eliminate methanol (it is not in its conjugate base form) because there are stronger bases among the answer choices.

Now we can look at the real bases. Sodium cyanide will yield the cyanide ion, which is an extremely strong nucleophile. Remember that the E2 competes with the SN2. This means that the cyanide ion will prefer performing the SN2 not the E2, so we can cross this answer choice off. 

Finally we are down to 2 answer choices, potassium hydroxide and sodium butoxide. Though potassium hydroxide is a strong base, it does not come close to the bulkiness of sodium butoxide. Thus, our best choice is sodium butoxide. 

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