All GRE Subject Test: Chemistry Resources
Example Question #2 : Reaction Mechanisms
What is created when a ketone is reacted with a phosphorus ylide?
The Wittig reaction involves a ketone or aldehyde reacting with a phosphorus ylide, a molecule with a negatively charged carbanion. The ketone will undergo nucleophilic addition and form a betaine. This intermediate will then form an alkene with a triphenylphosphine oxide being released. The Wittig reaction will form a mixture of both cis and trans isomers if the carbanion has two different substituents.
Wittig general reaction:
Example Question #202 : Gre Subject Test: Chemistry
Which of the following compounds would you expect to undergo a nucleophilic addition reaction?
When dealing with carbonyl compounds, remember that a carboxylic acid and all of its derivatives will undergo nucleophilic substitution. Aldehydes and ketones will undergo nucleophilic addition. Propanal is a three-carbon aldehyde, and will thus undergo nucleophilic addition.
Acetic acid is a carboxylic acid, methyl ethanoate is an ether, and ethanamide is an amide; each of these would undergo nucleophilic substitution.