1

Figure 4.3Examples of cycloalkane

nomenclature

Nomenclature

2

Introduction to Cycloalkanes

Figure 4.11 Three-dimensional structure

of some cycloalkanes

Chapter 8 3

Addition of HX (1)

Protonation of double bond yields the most stable carbocation. Positive charge goes to the carbon that was not protonated.

X =>

+ Br_

+

+CH3 C

CH3

CH CH3

H

CH3 C

CH3

CH CH3

H

H Br

CH3 C

CH3

CH CH3

Chapter 8 4

Addition of HX (2)

CH3 C

CH3

CH CH3

H Br

CH3 C

CH3

CH CH3

H+

+ Br_

CH3 C

CH3

CH CH3

H+

Br_

CH3 C

CH3

CH CH3

HBr

=>

Chapter 8 5

Mechanism for Hydration

+C

H

C+

H2O C

H

C

O H

H+

+ H2OC

H

C

O H

H+

C

H

C

OH

H3O++ =>

C C OH H

H

++ + H2OC

H

C+

Chapter 8 6

Orientation for Hydration

• Markovnikov product is formed.

+CH3 C

CH3

CH CH3 OH H

H

++ H2O+

H

CH3CH

CH3

CCH3

H2OCH3 C

CH3

CH CH3

HOH H

+

H2OCH3 C

CH3

CH CH3

HOH

=>

Chapter 8 7

Mechanism for Halogenation

• Pi electrons attack the bromine molecule.• A bromide ion splits off.• Intermediate is a cyclic bromonium ion.

CC + Br Br CC

Br

+ Br =>

Chapter 8 8

Mechanism (2)

Halide ion approaches from side opposite the three-membered ring.

CC

Br

Br

CC

Br

Br

=>

Chapter 8 9

Predict the Product

Predict the product when the given alkene reacts with chlorine in water.

CH3

D

Cl2, H2O

=>

OHCH3D

Cl

Chapter 8 10

Mechanism

One-step concerted reaction. Several bonds break and form simultaneously.

OC

O

R

H

C

C

OOH

OC

O

RC

C

+

=>

Chapter 8 11

One-Step Reaction

• To synthesize the glycol without isolating the epoxide, use aqueous peroxyacetic acid or peroxyformic acid.

• The reaction is stereospecific.

CH3COOH

O

OH

H

OH

H

=>

Chapter 8 12

Ozonolysis Example

CCCH3 CH3

H CH3 O3 C

H3C

H

O OC

CH3

CH3

O

Ozonide

+(CH3)2S

C

H3C

HO C

CH3

CH3

O CH3 S

O

CH3

DMSO

=>

13

• Compounds with two hydroxy groups are called diols or glycols.

• Compounds with three hydroxy groups are called triols.

Diols and Triols

14

• Epoxides can be named in three different ways—epoxyalkanes, oxiranes, or alkene oxides.

• To name an epoxide as an epoxyalkane, first name the alkane chain or ring to which the O atom is attached, and use the prefix “epoxy” to name the epoxide as a substituent.

• Use two numbers to designate the location of the atoms to which the O is bonded.

Naming Epoxides

15

• Alcohols and ethers are both common products of nucleophilic substitution.

• The preparation of ethers by the method shown in the last two equations is called the Williamson ether synthesis.

Preparation of Alcohols and Ethers

16

• An alkoxide salt is needed to make an ether.• Alkoxides can be prepared from alcohols by a Brønsted-Lowry

acid-base reaction. • For example, sodium ethoxide (NaOCH2CH3) is prepared by

treating ethanol with NaH.

• NaH is an especially good base for forming alkoxide because the by-product of the reaction, H2, is a gas that just bubbles out of the reaction mixture.

Preparation of Alkoxides

17

Substitution and Elimination Reactions of Alcohols

• Treatment of alcohols with a strong acid protonates the O converting the bad leaving group ¯OH into H2O, a good leaving group.

• This makes it possible to perform substitution and elimination reactions on alcohols.

18

• Typical acids used for alcohol dehydration are H2SO4 or p-toluenesulfonic acid (TsOH).

Dehydration Requires Strong Acids

• Dehydration is typically carried out using H2SO4 and other strong acids, or phosphorus oxychloride (POCl3) in the presence of an amine base.

19

• When an alcohol has two or three carbons, dehydration is regioselective and follows the Zaitsev rule.

• The more substituted alkene is the major product when a mixture of constitutional isomers is possible.

Zaitsev’s Rule

20

• 2° and 3° alcohols react by an E1 mechanism, whereas 1° alcohols react by an E2 mechanism.

Dehydration by E1 Mechanism

21

22

23

• Knowing the mechanism allows us to predict the stereochemistry of the products when the reaction occurs at a stereogenic center.

Stereochemistry of Reaction of Alcohols with HX

24

• When a 1° or 2° alcohol is treated with SOCl2 and pyridine, an alkyl chloride is formed, with HCl and SO2 as by-products.

• The mechanism of this reaction consists of two parts:

1. Conversion of the OH group into a better leaving group.

2. Nucleophilic substitution by Cl¯ via an SN2 reaction.

Conversion of Alcohols to Alkyl Chlorides with SOCl2

25

26

• Because alkyl tosylates have good leaving groups, they undergo both nucleophilic substitution and elimination, exactly as alkyl halides do.

• Generally, alkyl tosylates are treated with strong nucleophiles and bases, so the mechanism of substitution is SN2, and the mechanism of elimination is E2.

Substitution and Elimination of Tosylates

27

Figure 9.9

Opening an Epoxide Ring with HCl

28

Figure 9.10

Synthesis Using Opening of an Epoxide Ring

29

• When polyaromatic hydrocarbons are inhaled or ingested, they are oxidized in the liver to species that often contain a highly reactive epoxide ring.

• The strained three-membered ring reacts readily with biological nucleophiles such as DNA or enzymes, leading to ring-opened products that often disrupt cell function, causing cancer or cell death.

Health Effects of Epoxides