.

Alkyl Halides
• An organic compound containing at least one carbonhalogen 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
2

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

5

6

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

• 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
8

• 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),
9

• 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
10

• These are accepted by IUPAC
11

12

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
Hydrogen bonding in ethanol
Figure 4.4
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
13

Figure 4.5
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
14

• Acid – A proton (H + ) donor
• Base – A proton acceptor
Acid Base Conjugate Conjugate
Acid Base
15

Energy diagram for concerted proton transfer
Figure 4.6
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
16

HA H
+
+ A
-
K a

[ H

][ A
-
]
[ HA] pK a
  log K a
17

Relative Strengths of Some Common Acids and
Their Conjugate Bases
Acid
CH
3
CH
2
OH
H
2
O
HCN
CH
3
CO
2
H
HF
HNO
3
HCl
Name
Ethanol
Water
Hydrocyanic Acid
Acetic Acid
Hydrofluoric Acid
Nitric Acid
Hydrochloric Acid pK a
16.00
15.74
9.31
4.76
3.45
-1.3
-7.0
18

K a
The proton will always go from the stronger acid to the stronger base
H
H
C
H
O
C
Acetic Acid p K a
= 4.76
O
H
+ O H
Hydroxide Ion
H
H
C
O
C
H
Acetate Ion
O + H O
H
Water p K a
= 15.74
19

Organic Acids
20

• 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
21

22

H
2
O
HCl HNO
3 H
2
SO
4
H
H
C
H
C
O
O H
OH
H
H
C
H
H
C
H
O
H
Li
+ Mg
2+
AlCl
3
BF
3
FeCl
3
23

H
H
C
H
H
C
H
O
H
H
H O H
C C C
H H
H
H
H O
C C H
H
H
H
C
H
C
O
O H
H
H
C
H
C
O
H
O C
H
H
H
H H
C O C
H H
H
H
H H
C N C
H H H
H
24

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
25

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
26

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
27

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
28

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
29

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
30

Indicating Steps in Mechanisms
• Curved arrows indicate breaking and forming of bonds
• Arrowheads with a “half” head (“fishhook”) indicate homolytic and homogenic steps (called ‘radical processes’)
• Arrowheads with a complete head indicate heterolytic and heterogenic steps (called ‘polar processes’)
31

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
32

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
33

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 (

+)
34

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
35

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
36

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
37

Energy diagram for formation of tert -butyl chloride from tert -butyl alcohol and hydrogen chloride
Figure 4.7
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
38

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
39

Structure of methyl cation
Figure 4.8
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
40

Combination of a carbocation and a halide anion
Figure 4.11
Francis A. Carey, Organic Chemistry, Fourth Edition. Copyright © 2000 The McGraw-Hill Companies, Inc. All rights reserved.
41