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Chapter 3

Chapter 3. An Introduction to Organic Reactions and Their Mechanism Acids and Bases. Acid-Base Reaction. Acid-Base properties. Acid Properties: When dissolved in water, acids Conduct electricity Change blue litmus to red Have a sour taste

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Chapter 3

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  1. Chapter 3 An Introduction to Organic Reactions and Their Mechanism Acids and Bases

  2. Acid-Base Reaction

  3. Acid-Base properties • Acid Properties: • When dissolved in water, acids • Conduct electricity • Change blue litmus to red • Have a sour taste • React with bases to neutralize their properties • React with active metals to liberate hydrogen. • Base Properties: • When dissolved in water, bases • Conduct electricity • Change red litmus to blue • Have a slippery feeling • React with acids to neutralize their properties.

  4. 3.1 Reactions and Their Mechanism • Chemical equation: • Reactants  products • Atoms are neither created nor destroyed. • Four categories: substitution, additions, eliminations and rearrangement

  5. Substitution • Substitution: one group is replaced with another • General reaction

  6. Elimination • Atoms or groups are removed from adjacent atoms to form a double or triple bond • General reaction

  7. Addition • Atoms or groups add to adjacent atoms of a multiple bond • General reaction

  8. Rearrangement • A molecule undergoes a reorganization of its constituent parts. • Positions of the double bond and a hydrogen atom changed

  9. 3.1 Homolysis and Heterolysis of Covalent Bonds • When an organic reaction occurs, some covalent bonds must be break and a new bond must form. • A covalent bond can be broken in two ways: • Heterolysis • Bond cleavage in which bonding of electrons are unevenly divided between the two parting atoms • Homolysis • Bond cleavage in which bonding of electrons are evenly divided between the two parting atoms

  10. Homolysis and Heterolysis

  11. 3.2 Acid-Base Reactions • Bronsted-Lowry acids: an acid is a substance that can donate a proton (H+) • Bronsted-Lowry acids: an base is a substance that can accept a proton (H+)

  12. The Lewis Definition of Acids and Bases • Lewis acid is (electrons acceptor) • electrophiles • Lewis base is (electrons donor) • nucleophiles

  13. Lewis acids and bases

  14. Lewis Acids -Bases

  15. Combination of Site Type • The reaction site is • A polar bond because oxygen is more electronegative than carbon • A Lewis base since there are unshared pairs of electrons to the oxygen that can be shared with a Lewis acid • Multiple bond with a π bond in which electrons are available to incoming species

  16. Examples • Which of the following are potential Lewis acids and which are potential Lewis base? • Identify Lewis Base site

  17. Examples • Write equations showing the Lewis acid-base reaction that take place when: • Methanol (CH3OH) reacts with BF3

  18. Heterolysis of Bonds to Carbon: Carbocations and Carboanions

  19. Carbocations and Electrophiles • Electrophiles are reagent which in their reactions seek the extra electrons that will give them a stable valence of electrons

  20. Carbocations and Nucleophiles • Nucleophiles are reagents that seek a proton or some other positive center

  21. Examples • Classify the following as either electrophiles or nucleophiles • Use the curved-arrow notation to write the reaction what would take place between dimethylamine (CH3)2NH and boron trifluoride). Identify Lewis acid and Lewis Base

  22. 16.2 Acid Strength • Strong acids: completely ionized or completely dissociated • Forward reaction is predominated • Most of HA is dissociated • Conjugated base is weak and has low attraction for proton HA(aq) + H2O(l)  H3O+(aq) + A-(aq)

  23. Acids Strength • Weak acids: partially ionized or dissolved • Reverse reactions is predominated • Most of HA is undissociate • Conjugated base is strong and has high attraction for proton HC2H3O4(aq) + H2O(l) H3O+(aq) +C2H3O4-(aq)

  24. Acid Strength

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