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Alcohol and Alkyl Halides

Alcohol and Alkyl Halides. Chapter 3 . Alkyl Halides. An organic compound containing at least one carbon-halogen bond (C-X) X (F, Cl, Br, I) replaces H Can contain many C-X bonds Properties and some uses Fire-resistant solvents Refrigerants Pharmaceuticals and precursors.

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Alcohol and Alkyl Halides

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  1. Alcohol and Alkyl Halides Chapter 3.

  2. Alkyl Halides • An organic compound containing at least one carbon-halogen bond (C-X) • X (F, Cl, Br, I) replaces H • Can contain many C-X bonds • Properties and some uses • Fire-resistant solvents • Refrigerants • Pharmaceuticals and precursors

  3. Naming Alkyl Halides • Name is based on longest carbon chain • (Contains double or triple bond if present) • Number from end nearest any substituent (alkyl or halogen)

  4. Many Alkyl Halides That Are Widely Used Have Common Names • Chloroform • Carbon tetrachloride • Methylene chloride • Methyl iodide • Trichloroethylene

  5. Alcohols • Alcohols contain an OH group connected to a a saturated C (sp3) • They are important solvents and synthesis intermediates • Phenols contain an OH group connected to a carbon in a benzene ring • Methanol, CH3OH, called methyl alcohol, is a common solvent, a fuel additive, produced in large quantities • Ethanol, CH3CH2OH, called ethyl alcohol, is a solvent, fuel, beverage • Phenol, C6H5OH (“phenyl alcohol”) has diverse uses - it gives its name to the general class of compounds

  6. Naming Alcohols • General classifications of alcohols based on substitution on C to which OH is attached • Methyl (C has 3 H’s), Primary (1°) (C has two H’s, one R), secondary (2°) (C has one H, two R’s), tertiary (3°) (C has no H, 3 R’s),

  7. IUPAC Rules for Naming Alcohols • Select the longest carbon chain containing the hydroxyl group, and derive the parent name by replacing the -e ending of the corresponding alkane with -ol • Number the chain from the end nearer the hydroxyl group • Number substituents according to position on chain, listing the substituents in alphabetical order

  8. Many Alcohols Have Common Names • These are accepted by IUPAC

  9. Hybridization of Methanol

  10. Properties of Alcohols: Hydrogen Bonding • The structure around O of the alcohol or phenol is similar to that in water, sp3 hybridized • Alcohols and phenolshave much higher boiling points than similar alkanes and alkyl halides

  11. H-Bonding between Ethanol and Water

  12. Acids and BasesThe Brønsted-Lowry Definition • Acid – A proton (H+) donor • Base – A proton acceptor Acid Base Conjugate Conjugate Acid Base

  13. Acid and Base Strength

  14. Relative Strengths of Some Common Acids and Their Conjugate Bases

  15. Predicting Acid – Base Reactions from pKa Values The proton will always go from the stronger acid to the stronger base Acetic Acid Hydroxide Ion Acetate Ion Water pKa = 4.76 pKa = 15.74

  16. Organic Acids

  17. Lewis Acids and Bases • Lewis Acid – electron-pair acceptor • Lewis Base – electron-pair donor • Lewis Acids usually have at least one empty orbital • Lewis Bases usually have at least one set of paired electrons

  18. Examples of Lewis Acids

  19. Examples of Lewis Bases

  20. Kinds of Organic Reactions • In general, we look at what occurs and try to learn how it happens • Common patterns describe the changes • Addition reactions – two molecules combine • Elimination reactions – one molecule splits into two • Substitution – parts from two molecules exchange • Rearrangement reactions – a molecule undergoes changes in the way its atoms are connected

  21. How Organic Reactions Occur: Mechanisms • In a clock the hands move but the mechanism behind the face is what causes the movement • In an organic reaction, we see the transformation that has occurred. The mechanism describes the steps behind the changes that we can observe • Reactions occur in defined steps that lead from reactant to product

  22. Steps in Mechanisms • We classify the types of steps in a sequence • A step involves either the formation or breaking of a covalent bond • Steps can occur in individually or in combination with other steps • When several steps occur at the same time they are said to be concerted

  23. Types of Steps in Reaction Mechanisms • Formation of a covalent bond • Homogenic or heterogenic • Breaking of a covalent bond • Homogenic or heterogenic • Oxidation of a functional group • Reduction of a functional group

  24. Breaking of Covalent Bonds Homolytic Cleavage • Each product gets one electron from the bond • Not common in organic chemistry Heterolytic Cleavage • Both electrons from the bond that is broken become associated with one resulting fragment • A common pattern in reaction mechanisms

  25. Formation of a Bond Homogenic • One electron comes from each fragment • No electronic charges are involved • Not common in organic chemistry Heterogenic • One fragment supplies two electrons • One fragment supplies no electrons • Combination can involve electronic charges • Common in organic chemistry

  26. Indicating Steps in Mechanisms • Curved arrows indicate breaking and forming of bonds • Arrowheads with a “half” head (“fish-hook”) indicate homolytic and homogenic steps (called ‘radical processes’) • Arrowheads with a complete head indicate heterolytic and heterogenic steps (called ‘polar processes’)

  27. 5.6 Using Curved Arrows in Polar Reaction Mechanisms • Curved arrows are a way to keep track of changes in bonding in polar reaction • The arrows track “electron movement” • Electrons always move in pairs • Charges change during the reaction • One curved arrow corresponds to one step in a reaction mechanism

  28. 5.4 Polar Reactions and How They Occur • Molecules can contain local unsymmetrical electron distributions due to differences in electronegativities • This causes a partial negative charge on an atom and a compensating partial positive charge on an adjacent atom • The more electronegative atom has the greater electron density

  29. Electronegativity of Some Common Elements • The relative electronegativity is indicated • Higher numbers indicate greater electronegativity • Carbon bonded to a more electronegative element has a partial positive charge (+)

  30. Polarizability • Polarization is a change in electron distribution as a response to change in electronic nature of the surroundings • Polarizability is the tendency to undergo polarization • Polar reactions occur between regions of high electron density and regions of low electron density

  31. Generalized Polar Reactions • An electrophile, an electron-poor species, combines with a nucleophile, an electron-rich species • An electrophile is a Lewis acid • A nucleophile is a Lewis base • The combination is indicate with a curved arrow from nucleophile to electrophile

  32. 10.7 Preparing Alkyl Halides from Alcohols • Reaction of tertiary C-OH with HX is fast and effective • Add HCl or HBr gas into ether solution of tertiary alcohol • Primary and secondary alcohols react very slowly and often rearrange, so alternative methods are used

  33. 5.10 Describing a Reaction: Intermediates • If a reaction occurs in more than one step, it must involve species that are neither the reactant nor the final product • These are called reaction intermediates or simply “intermediates” • Each step has its own free energy of activation • The complete diagram for the reaction shows the free energy changes associated with an intermediate

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