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

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)

5

6

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 (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

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, sp3 hybridized

• Alcohols and phenolshave much higher boiling points than similar alkanes and alkyl halides

14

H-Bonding between Ethanol and Water

15

Acids and BasesThe Brønsted-Lowry Definition

• Acid – A proton (H+) donor• Base – A proton acceptor

Acid Base Conjugate Conjugate

Acid Base

16Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.

Energy diagram for concerted proton transferFigure 4.6

17

Acid and Base Strength

HA H+ + A-

HA][

]A][H[ -

aK

aa KpK log

18

Relative Strengths of Some Common Acids and Their Conjugate Bases

Acid Name pKa

CH3CH2OH Ethanol 16.00

H2O Water 15.74

HCN Hydrocyanic Acid 9.31

CH3CO2H Acetic Acid 4.76

HF Hydrofluoric Acid 3.45

HNO3 Nitric Acid -1.3

HCl Hydrochloric Acid -7.0

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Predicting Acid – Base Reactions from pKa Values

The proton will always go from the stronger acid to the stronger base

C

H

H

H

C

O

O

H

O H CH C

H

H

O

O H O

H

+ +

Acetic Acid Hydroxide Ion Acetate Ion Water

pKa = 4.76 pKa = 15.74

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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 AcidsH2O HCl HNO3 H2SO4

C

H

H

H

CO

O H

OH

C

H

H

H

C

H

H

O

H

Li+ Mg2+AlCl3 BF3 FeCl3

24

Examples of Lewis Bases

C

H

H

H

CO

O H

C

H

H

H

C

H

H

O

H

C N C

H

H

H

H

H

H H

C C H

H

H

H

O

C C C

H

H

H

H

H

H

O

C

H

H

H

CO

O C

H

H

H

C O C

H

H

H

H

H

H

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

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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

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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

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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

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Formation of a BondHomogenic• 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

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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’)

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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

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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

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

37

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

38Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.

Energy diagram for formation of tert-butyl chloride from tert-butyl alcohol and hydrogen chlorideFigure 4.7

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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

40Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.

Structure of methyl cationFigure 4.8

41Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.

Combination of a carbocation and a halide anionFigure 4.11