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Example Questions
Example Question #1 : Benzene Additions
Choose the substituent that will direct meta addition on a benzene ring.
is the correct answer. In most cases, the deactivating substituents direct "meta." Halogens deactivate benzene rings, but are the exception, as they direct "ortho" or "para." A substituent is deactivating when it has a low electron concentration on the atom directly attached to the benzene ring. Carboxylic acid provides resonance, a delocalization of electrons. However, the amine group, for example, sees a lone pair on the nitrogen.
Example Question #1 : Benzene Additions
After the electrophilic aromatic substitution reaction occurs, in what position will the bromine be directed?
Ortho
Para
Meta
Two of these
Meta
The functional group that is already on the phenyl is the group that dictates where any other substituent will be directed on the ring. In this case, we have a carboxylic acid as our director. Due to resonance, carboxylic acid deactivates (is an electron-withdrawing group) the benzene ring and directs the bromine to the meta position.
Example Question #1 : Assigning Ortho, Meta, Para
An organic chemist wants to brominate the pictured benzene ring via an electrophilic aromatic substitution (EAS) reaction. On which position will the bromine attach?
Here we have a classic EAS reaction.
If we examine the molecule, we see that the benzene ring already has two substituents on it: , an activating group, and
, a deactivating group. Remember, when assigning the position of a new substituent to a benzene ring, activating groups always dictate the position of the new substituent.
We know that activating groups direct new substituents to the ortho or para positions. However, because of sterics, a new substituent will not be directed to the ortho position in between two substituents. Thus, the new substituent will be directed to the para position (or the other ortho position, but that is not one of our answer choices), and the correct answer is position 2.
Example Question #1 : Assigning Ortho, Meta, Para
Which of these functional groups is a meta director?
None of these
None of these
With the exception of halogens, meta directors deactivate a benzene ring. In other words, they make the benzene ring less reactive, especially in an electrophilic aromatic substitution (EAS) reaction. Meta directors have little electron density at the point of contact with the benzene ring. For example, a carboxylic acid is a meta director because it experiences resonance, a delocalization of electrons. All of the answer choices in this problem have a lone pair of electrons on the point of contact with the benzene ring and they all are ortho/para directors.
Example Question #1 : Stereochemistry
Which of the following are electron withdrawing substituents?
4 and 5
1, 4 and 5
2 and 4
1 and 2
3, and 4
1, 4 and 5
Carbonyls (as in 4 and 5) are always electron withdrawing due to the Oxygen's electronegativity. Similarly, the oxygens on the nitrate (1) are electron withdrawing.
Example Question #1 : Benzene Additions
What is the best explanation for why phenol (shown) directs substitution products ortho and para?
Resonance structures exist that put slight positive charges on meta positions.
Resonance structures exist that put slight negative charges on meta positions.
None of the other answers
Resonance structures exist that put slight positive charges on ortho and para positions.
Resonance structures exist that put slight negative charges on ortho and para positions.
Resonance structures exist that put slight negative charges on ortho and para positions.
Phenol contains the hydroxide group, which is an electron donor, puts electron density into the benzene ring. Resonance structures are drawn as follows
Example Question #1 : Assigning Ortho, Meta, Para
Which of the following substituents is electron-withdrawing when added to a benzene ring?
None of these substituents are electron-withdrawing
is the only electron-withdrawing substituent because it contains two electronegative oxygen atoms which pull electrons from the benzene ring towards itself. This effect is electron-withdrawing and makes the ring slightly positive in charge. All the other substituents are electron-donating groups, which activate the ring for electrophilic addition.
Example Question #1 : Stereochemistry
Which of the following groups would be added on the para position to phenol?
is the only electron-donating group listed. Therefore, it will add to the ortho and para positions on phenol. The rest of the substituents are highly electron-withdrawing groups and will add to the meta positions on phenol.
Example Question #1 : Benzene Additions
Which position will be most favored when adding chlorine to tert-butylbenzene?
Ortho
Ortho and para
Meta and para
Meta
Para
Para
A tert-butyl functional group is electron donating and will therefore activate the ortho and para positions. However, the ortho positions are sterically hindered by the bulky tert-butyl group. Therefore, the para position will be favored.
Example Question #1 : Benzene Additions
What is a major product of the reaction shown?
I only
II only
III only
II and III
I only
In the molecule shown, the nitro group will direct incoming substituents to positions meta to it, and the methoxy group will direct incoming substituents ortho or para to it. The only product option shown in which the chlorine substituent is meta (1,3) to the nitro group AND either ortho (1,2) or para (1,4) to the methoxy group is option I.
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