Question

Identify the likely electrophilic and nucleophilic sites in each of the following molecules:

a.

testosterone

b.

Methamphetmine

Short answer

To determine the electrophilic and nucleophilic position, we need to look at where the electrons are located in the molecule. All aliphatic positions will be ignored due to the lack of polarization or lone pairs.

Step-by-step solution

Electrophilic and nucleophilic position

To determine the electrophilic and nucleophilic position, we need to look at where the electrons are located in the molecule. All aliphatic positions will be ignored due to the lack of polarization or lone pairs.

Testosterone nucleophilic sites

For testosterone, one group is east to determine that is the secondary alcohol as it is very rich in electrons due to the presence of lone pairs. As such it will be nucleophilic.

The other heteroatom in testosterone, the oxygen of the ketone has two lone pairs about it and therefore, it has a high degree of electron density. However, there is one thing that holds this ketone back from being a likely nucleophilic position.

If the oxygen of the ketone were to attack a nucleophile, the resulting cationic species puts a high degree of positive charge on the carbon of the ketone as well. This can be seen through the use of resonance structures shown as:

Resonance structure

The resulting carbocation is very unstable and results in the diminishment of nucleophilicity for the ketone.

Testosterone electrophilic sites

For electrophilic sites, we need to look at sites where the electron density is poor. Also, these regions must have a leaving group. A leaving group can be a pair of electrons but these electrons must end up om a heteroatom or in a stabilized conjugated system.

By looking at ketone we may observe that the carbon lacks electron density due to the polarization of the C=O bond. This can also be seen through the use of resonance structures as shown:

Resonance structures

The carbocation can be even further delocalized through conjugation with the adjacent alkene as shown below:

Conjugation with alkene

Thus, wherever the carbocation is located in each of the resonance structures, there is a corresponding electrophilic position that is shown as: