Organic Chemistry : Identifying Electrophiles

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Identifying Electrophiles

The molecule pictured is known as rapamycin, or Sirolimus, and is used as an immunosuppressant during organ transplants. Which of the following colored carbonyl groups is the most electrophilic?


        Q7

Possible Answers:

Purple

Gold

Blue

Green

Red

Correct answer:

Gold

Explanation:

Note that many of these carbonyl groups are actually part of various functional groups. For example, the gold is an aldehyde, the green and purple are both ketones, the red is an amide, and the blue is an ester. We know the electrophilicity of carbonyl-containing functional groups is as follows:

 

A7 

Thus, our aldehyde, in gold, is the most electrophilic.

Example Question #2 : Identifying Electrophiles

Which compound is not a Lewis acid?

Possible Answers:

All of the given compounds are Lewis acids

Correct answer:

Explanation:

A Lewis acid is an electron pair acceptor. A Lewis base is an electron pair donor.

 is an ionic molecule and is neutral.  and  have positive charges and are electron pair acceptors, as they are more stable when they are neutral.

The correct answer, , has a lone pair on the nitrogen atom that can be donated to form bonds with other atoms, so it is a Lewis base.

Example Question #1 : Identifying Electrophiles

Which of these is a typical electrophile?

Possible Answers:

Ammonia

Iodide ion

Methyl carbocation

Chloride ion

Correct answer:

Methyl carbocation

Explanation:

Electrophiles are substances that accept an electron pair to form a covalent bond, and nucleophiles are those that donate an electron pair to form a covalent bond. The chloride and iodide ions are both nucleophiles, as they each have a charge of  and would thus be willing to donate their extra electron. Ammonia () is also a nucleophile, as the nitrogen has a lone pair of electrons to donate. The methyl carbocation (carbon attached to three hydrogen atoms, with a positive charge) is an electrophile. The positive charge on the carbon makes it willing to accept an electron pair to form a covalent bond.

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