Pharmaceutical Organic Chemistry-I: Electrophilic Substitution
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Questions and Answers

What characterizes the nitro group in terms of its effect on the benzene ring?

  • It has electron-withdrawing effects which deactivate the ring. (correct)
  • It is an electron-donating group.
  • It increases the electron density of the benzene ring.
  • It stabilizes the σ-complex intermediate during SE reactions.

    • Which of the following groups is considered a powerful deactivating group with a -M effect?

  • -Cl
  • -COOH (correct)
  • -OH
  • -Br

    • Why do halogens act as o-, p- directing groups despite being deactivating?

  • Their -I effect dominates over their +M effect.
  • They have no significant effects on the electron density.
  • They do not affect the rate of substitution reactions.
  • Their +M effect is stronger than their -I effect. (correct)

    • Which of the following groups would destabilize a σ-complex intermediate formed during electrophilic substitution?

    <p>-NO2</p> Signup and view all the answers

    Which of the following describes a moderate deactivating group?

    <p>-CF3</p> Signup and view all the answers

    Which group has a +M effect that increases electron density in a benzene ring?

    <p>-NH2</p> Signup and view all the answers

    What characterizes an alkyl group in benzene with respect to electrophilic substitution?

    <p>-1</p> Signup and view all the answers

    Which of the following groups would be classified as a moderate activating group?

    <p>-1</p> Signup and view all the answers

    What is the effect of a hydroxy group on a benzene ring during electrophilic substitution?

    <p>-2</p> Signup and view all the answers

    What is the impact of electron-withdrawing groups on electrophilic substitution?

    <p>Decrease the rate of substitutions</p> Signup and view all the answers

    Which statement is true about alkyl groups in terms of directing effects during substitution?

    <p>They are p-directing</p> Signup and view all the answers

    What role does resonance play in stabilizing σ-complex intermediates formed from hydroxy group substitution?

    <p>It stabilizes through delocalization of positive charge</p> Signup and view all the answers

    Which of the following groups is not a powerful activating group?

    <p>-COOH</p> Signup and view all the answers

    Which group is classified as an electron withdrawing group?

    <p>-CHO</p> Signup and view all the answers

    What type of director are -OH and -OR groups considered in electrophilic substitution reactions?

    <p>Ortho-para directors</p> Signup and view all the answers

    Which of the following groups would increase the rate of electrophilic substitution reactions?

    <p>-NR2</p> Signup and view all the answers

    What effect does an electron withdrawing group have on the benzene ring?

    <p>Decreases reactivity</p> Signup and view all the answers

    Which of the following is an example of a group with a +I effect?

    <p>-R</p> Signup and view all the answers

    Which type of substituent directs the incoming electrophile to the meta position?

    <p>Meta directors</p> Signup and view all the answers

    Which substituent would be classified as activating and o-, p- directing in electrophilic substitution?

    <p>-NR2</p> Signup and view all the answers

    Which of the following represents a group with a -M effect?

    <p>-NO2</p> Signup and view all the answers

    What does the strength of the mesomeric effect of chlorine compared to other substituents indicate?

    <p>Chlorine's p orbital is larger than carbon's, leading to weaker overlap and less effective overlap.</p> Signup and view all the answers

    In the case of a compound with multiple rings, if one ring is activated and another is deactivated, how will the reaction proceed with excess reactant?

    <p>It will occur in the activated ring and both m- positions of the deactivated ring.</p> Signup and view all the answers

    When two substituents in a disubstituted benzene reinforce each other, what happens during the nitration of p-nitrotoluene?

    <p>Both substituents direct the incoming group to the same position.</p> Signup and view all the answers

    Which of the following statements about activating and deactivating groups is true?

    <p>Activating groups usually have stronger directing effects than deactivating groups.</p> Signup and view all the answers

    What occurs when the directing effects of two opposing substituents have approximately equal ability?

    <p>A mixture of products will be produced.</p> Signup and view all the answers

    Which reaction condition would likely lead only to the ortho and para positions when reacting with an equimolar concentration of reactants?

    <p>Equimolar concentrations of both reactants.</p> Signup and view all the answers

    In the context of bromination of p-toluidine, which statement is accurate regarding the effect of substituent groups?

    <p>The effect of the activating group determines the orientation of bromination.</p> Signup and view all the answers

    What is expected in the monobromination of a specific compound with Br2 and FeBr3?

    <p>Multiple brominated products will occur normally.</p> Signup and view all the answers

    Study Notes

    PharmD Program Fall 2024 - Pharmaceutical Organic Chemistry-I (PC 102)

    • Course instructor: Dr. Ehab Gedawy
    • Course: Pharmaceutical Organic Chemistry-I (PC 102)
    • Course year: Fall 2024
    • Course covers: Chemistry of Aromatic Compounds (Lecture 8)

    Reactivity & Orientation in Electrophilic Aromatic Substitution (SE) Reactions

    • Substituents affect the rate of SE reactions (reactivity).
    • Electron-donating groups (+M effect) increase electron density in the ring, making it more reactive towards electrophiles (E+). Examples include -NH2, -NHR, -NR2, -OH, -OR, -OCOR, and -NHCOR.
    • Electron-withdrawing groups (-M effect) decrease electron density in the ring, making it less reactive and slower to react with electrophiles (E+). Examples include -CHO, -COR, -COOH, -COOR, -CONH2, -SO3H, -C=N, -NO2, -NH3+, -CF3, -CCl3.

    Position of the Incoming Substituent (Orientation)

    • Substituents direct the incoming group to specific positions in the ring.
    • Ortho/para directors: Direct incoming groups to ortho (adjacent) or para (opposite) positions. Common examples include activating groups -NH2, -NHR, -NR2, -OH, -OR, -OCOR, -NHCOR, and -R, -Ar, -F, -Cl, -Br, -I.
    • Meta directors: Direct incoming groups to the meta (intermediate) position. Examples include deactivating groups -CHO, -COR, -COOH, -COOR, -CONH2, -SO3H, -C=N, -NO2, -NH3+, -CF3, -CCl3.

    Activating (Electron-Donating) & o-, p-Directing Groups

    • Powerful activating groups (+M effect):
      • Contain electron-donating groups with lone pairs directly bonded to the ring (e.g., -NH2, -OH, -OR).
    • Moderate activating groups (+I effect):
      • Contain alkyl groups (-R) or aryl groups (-Ar). These stabilize the intermediate carbocation through inductive effects.
    • Examples include alkyl groups (-R, like methyl, ethyl), aryl groups (-Ar), electron-donating groups (-NH2, -OH, -OR, etc.).

    Deactivative (Electron-Withdrawing) & m- Directing Groups

    • Powerful deactivating groups (-M effect):
      • Contain electron-withdrawing groups directly linked to the ring (e.g., -CHO, -COR, -COOH, -COOR, -SO3H, -NO2, etc).
    • Moderate deactivating groups (-I effect):
      • Contain halogen atoms (-F, -Cl, -Br, -I) or groups like -CF3, -CCl3.

    Halogens as o-,p- Directing Deactivating Groups

    • Halogens exhibit both electron-withdrawing (-I effect) and electron-donating (+M effect).
    • The -I effect is stronger than the +M effect, resulting in halogen substituents being deactivating.
      • Still direct a substituent to ortho or para positions.
    • The difference in orbital size between carbon and halogen atoms impacts the strength of mesomeric effects.

    Summary

    • Different groups (activating/deactivating) influence the reactivity and orientation of electrophilic substitution reactions in aromatic rings.
    • Substituent effects (including +M & -M, +I & -I) determine whether a group enhances reaction speed or hinders it, as well as where new groups attach on the ring.

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    PharmD Program Fall 2024 Lecture 8 PDF

    Description

    This quiz covers Lecture 8 of Pharmaceutical Organic Chemistry-I (PC 102), focusing on the reactivity and orientation in electrophilic aromatic substitution reactions. You'll learn about the effects of different substituents on reaction rates and orientation, such as electron-donating and electron-withdrawing groups.

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