Download Haloalkanes: Nomenclature, Substitution and Elimination Reactions - Prof. Cheng-Wei T. Cha and more Study notes Organic Chemistry in PDF only on Docsity! 1 Chapter 7. Haloalkanes Learning objectives: 1. Provide both IUPAC and common names for haloalkanes. 2. Differentiate primary, secondary, and tertiary alkyl halides. 3. Write the general electron-pushing (arrow-pushing) mechanisms for SN1 and SN2 reactions. 4. Draw the potential energy diagrams for SN1 and SN2 reactions. 5. Predict the favored reaction between SN1 and SN2 mechanisms for a given haloalkane based on the structures of haloalkanes, the structures of nucleophiles, leaving groups, and solvents. 6. Write the general electron-pushing (arrow-pushing) mechanisms for E1 and E2 reactions. 7. Draw the potential energy diagrams for E1 and E2 reactions. 8. Predict the favored reaction between E1 and E2 mechanisms for a given haloalkane based on the structures of haloalkanes, the strengths of bases, and leaving groups. 9. Predict the major product(s), including the stereochemistry, of elimination reactions. Sections to be covered (in the order of delivery): 7.1 Introduction # 7.2 Nomenclature 7.3 Nucleophilic Aliphatic Substitution and β-Elimination * 7.4 Nucleophilic Aliphatic Substitution * 7.5 Mechanisms of Nucleophilic Aliphatic Substitution * 7.6 Experimental Evidence for SN1 and SN2 Mechanisms 7.7 Analysis of Several Nucleophilic Substitution Reactions 7.8 β-Elimination * 7.9 Mechanisms of β-Elimination * 7.10 Substitution Versus Elimination * * Sections that will be focused # Sections that will be skipped Recommended additional problems 7.7 – 7.40, 7.43 2 7.2 Nomenclature A. IUPAC Names Br Br Br OH Br Br Br OH Cl OH CH3 Cl B. Common Names F Cl CH2Cl2 CHCl3 5 (i) Inversion of Configuration: Issue on Stereoselectivity of SN2 Mechanism (ii) Energy Diagram B. SN1 Mechanism Rate = k·[haloalkane] (i) Br H3C H3C H3C CH3 H3C CH3 Br+ 6 CH3 H3C CH3 CH3O H CH3 O CH3 CH3H H3C + CH3 O CH3 CH3H H3C CH3 O CH3 CH3 H3C B BH+ + (ii) Energy Diagram 7 (iii) Racemization of Stereocenter: Issue on Stereoselectivity of SN1 Mechanism 7.6 Experimental Evidence for SN1 and SN2 Mechanisms A. Structure of the Nucleophile Know how to classify strong and weak nucleophiles (relative nucleophility) (Table 7.2) B. Structure of the Haloalkane 10 7.8 β-Elimination Zaitsev’s rule: Br NaOCH3 CH3OH Cl NaOMe MeOH + I II (Notice: Me = CH3, methyl group) Cl NaOMe MeOH + + I II III 11 7.9 Mechanisms of β-Elimination A. E1 Mechanism Br H3C H3C H3C CH3 H3C CH3 Br+ CH3 H3C H2C H B+ CH3 H3C CH2 + BH B. E2 Mechanism Br H3C H3C H2C H B+ CH3 H3C CH2 + BH Br+ 12 7.10 Substitution Versus Elimination A. SN1 vs. E1 Reactions B. SN2 vs. E2 Reactions
