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

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4 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)

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

8 Alcohols Alcohols contain an OH group connected to a a saturated C (sp 3 ) They are important solvents and synthesis intermediates Phenols contain an OH group connected to a carbon in a benzene ring Methanol, CH 3 OH, called methyl alcohol, is a common solvent, a fuel additive, produced in large quantities Ethanol, CH 3 CH 2 OH, called ethyl alcohol, is a solvent, fuel, beverage Phenol, C 6 H 5 OH (“phenyl alcohol”) has diverse uses - it gives its name to the general class of compounds

9 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),

10 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

11 Many Alcohols Have Common Names These are accepted by IUPAC

12 Hybridization of Methanol

13 Properties of Alcohols: Hydrogen Bonding The structure around O of the alcohol or phenol is similar to that in water, sp 3 hybridized Alcohols and phenolshave much higher boiling points than similar alkanes and alkyl halides

14 H-Bonding between Ethanol and Water

15 Acids and Bases The Brønsted-Lowry Definition Acid – A proton (H + ) donor Base – A proton acceptor AcidBase Conjugate Conjugate Acid Base

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17 Acid and Base Strength

18 Relative Strengths of Some Common Acids and Their Conjugate Bases AcidNamepKapKa CH 3 CH 2 OHEthanol16.00 H2OH2OWater15.74 HCNHydrocyanic Acid9.31 CH 3 CO 2 HAcetic Acid4.76 HFHydrofluoric Acid3.45 HNO 3 Nitric Acid-1.3 HClHydrochloric Acid-7.0

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

20 Organic Acids

21 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

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23 Examples of Lewis Acids

24 Examples of Lewis Bases

25 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

26 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

27 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

28 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

29 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

30 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

31 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’)

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

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

34 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 (  +)

35 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

36 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

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

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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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