Lectures 4 Nomenclature for student 2013-2014 BW

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LECTURE 4

Dr Ali El-Agamey

CHEM-103:

BASIC ORGANIC CHEMISTRY

DAMIETTA UNIVERSITY

2 ©2010, Prentice Hall

Preparations and reactions of Alkenes

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3 Chapter 7

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Heat of Hydrogenation •  Combustion of an alkene and hydrogenation of an

alkene can provide valuable data as to the stability of the double bond.

•  The more substituted the double bond, the lower its heat of hydrogenation, the greater stability of the alkene.

4 Chapter 7

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Heat of Hydrogenation •  The more substituted the double bond, the

lower its heat of hydrogenation, the greater stability of the alkene.

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5 Chapter 7 5

Disubstituted Isomers •  Stability: cis < geminal < trans isomer •  The less stable isomer has a higher exothermic

heat of hydrogenation.

-116 kJ trans-2-butene

-117 kJ (CH3)2C=CH2 iso-butene

-120 kJ cis-2-butene

6 Chapter 7 6

Relative Stabilities

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Preparation of Alkenes

(1) Dehydrohalogenation of alkyl halide; (2) Dehalogenation of vicinal dihalides; (3) Dehydration of alcohols; (4) Reduction of Alkynes (1) Dehydrohalogenation of alkyl halide; (2) Dehalogenation of vicinal dihalides; (3) Dehydration of alcohols; (4) Reduction of Alkynes

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Preparation of Alkenes

Main product Minor product

Main product Minor product

cis-But-2-ene trans-But-2-ene

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(1) Reactions of Alkenes

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Regioselectivity •  Markovnikov’s Rule: The addition of a proton

to the double bond of an alkene results in a product with the acidic proton bonded to the carbon atom that already holds the greater number of hydrogens.

•  Markovnikov’s Rule (extended): In an electrophilic addition to the alkene, the electrophile adds in such a way that it generates the most stable intermediate.

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11 Chapter 8 11

Influence of peroxides

anti-Markovnikov addition

Markovnikov addition

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Show how you would accomplish the following synthetic conversions:

(a) Convert 1-methylcyclohexene to 1-bromo-1-methylcyclohexane.

(b) Convert 1-methylcyclohexene to 1-bromo-2-methylcyclohexane.

(c) Convert 1-methylcyclohexanol to 1-bromo-2-methylcyclohexane.

Problems

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Halohydrin

anti-Markovnikov addition

(BH3)2 is called diborane

(1) Halohydrin formation; (2) Hydration (addition of water)

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Epoxide

HCO2OH is called peroxyacid

1,2-Diol 1,2-Diol

(1) Ozonolysis; (2) Hydroxylation; (3) Epoxidation

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15 Chapter 8

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Ozonolysis of an unknown alkene gives an equimolar mixture of cyclohexanecarbaldehyde and 2-butanone. Determine the structure of the original alkene.

Solved Problem

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Ozonolysis of an unknown alkene gives an equimolar mixture of cyclohexanecarbaldehyde and 2-butanone. Determine the structure of the original alkene.

Solved Problem

Solution

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17 Chapter 8

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Ozonolysis of an unknown alkene gives compound A. Determine the structure of the original alkene.

Problem

A

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Ozonolysis of an unknown alkene gives compound A. Determine the structure of the original alkene.

Solved Problem

Solution

A

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19 Chapter 8

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Homework

(1) What are the products of the ozonolysis of (a) 2-hexene (b) 3-hexene.

(2) Ozonolysis of an unknown alkene gives acetone and formaldehyde. Determine the structure of the original alkene.

Homework


(2) Ozonolysis of an unknown alkene gives acetone and formaldehyde. Determine the structure of the original alkene.

Homework


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(1) Show how you would convert 1-methylcyclopentanol to 2-methylcyclopentanol.

Problems

(2) Show how you would prepare 1-bromopropane from 2-bromopropane.

(3) Show how you would prepare 1,2-epoxypropane from 2-propanol.



(1) Show how you would convert 1-methylcyclopentanol to 2-methylcyclopentanol.



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Nomenclature of Ethers

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Nomenclature of ethers

  (1) Ethers are named in IUPAC nomenclature as alkoxyalkane. Use more complex alkyl group as the parent name

Methoxyethane

3-Ethoxy-1,1-dimethylcyclohexane

Chloromethoxymethane Ethoxyethane


Methoxyethane


Methoxyethane


Ethoxyethane Methoxyethane


Ethoxyethane Methoxyethane



Chloromethoxymethane Ethoxyethane Methoxyethane



Chloromethoxymethane Ethoxyethane Methoxyethane

Nomenclature of ethers Nomenclature of ethers

Methoxyethane


Methoxyethane


Chloromethoxymethane


Chloromethoxymethane

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Homework: Write the IUPAC name of the following compounds


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Alkyl Halides

©2010, Prentice Hall

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25 Chapter 6 25

Uses of Alkyl Halides •  Industrial and household cleaners. •  Anesthetics:

–  CHCl3 used originally as general anesthetic but it is toxic and carcinogenic.

–  CF3CHClBr is a mixed halide sold as Halothane® •  Freons are used as refrigerants and foaming agents.

–  Freons can harm the ozone layer so they have been replaced by low-boiling hydrocarbons or carbon dioxide.

•  Pesticides such as DDT are extremely toxic to insects but not as toxic to mammals. –  Haloalkanes can not be destroyed by bacteria so

they accumulate in the soil to a level which can be toxic to mammals, especially, humans.

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Alkyl Halides Classification •  Methyl halides: halide is attached to a methyl

group. •  Primary alkyl halide: carbon to which halogen

is bonded is attached to only one other carbon. •  Secondary alkyl halide : carbon to which

halogen is bonded is attached to two other carbons.

•  Tertiary alkyl halide : carbon to which halogen is bonded is attached to three other carbon.

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primary alkyl halide secondary alkyl halide

tertiary alkyl halide

Primary, Secondary, Tertiary Alkyl Halides

*

* *

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Types of Dihalides

•  Geminal dihalide: two halogen atoms are bonded to the same carbon.

•  Vicinal dihalide: two halogen atoms are bonded to adjacent carbons.

geminal dihalide

vicinal dihalide

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1 2 3 4 5 6 7 8 9

6-bromo-2-methylnonane

3 1 2 4

2-chlorobutane

  (1) Alkyl halides are named in IUPAC nomenclature as haloalkane. F: fluoro-; Cl: chloro-; Br: bromo-; I: iodo-

Nomenclature of alkyl halides

1 2 3 4 5 6 7 8 9


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1 2 3 4 5 6 7 8 9


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Write the IUPAC names of the following compounds

Fluoroethane 1-Chlorobutane 2-Bromopropane

Iodocyclohexane

1-Chloro-3-methylcyclopentane

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Homework: Write the structures for the following compounds

  (i) 1,1-Dibromopropane (ii) 3-Bromo-2-methylpentane

  (iii) 2-Bromo-3-ethyl-2-methylhexane

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Preparation of Alkyl halides

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Preparation of Alkyl halides

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Polarity and Reactivity

•  Halogens are more electronegative than C. •  Carbon—halogen bond is polar, so carbon has partial

positive charge. •  Carbon can be attacked by a nucleophile. •  Halogen can leave with the electron pair.

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•  The halogen atom on the alkyl halide is replaced with a nucleophile (Nuc-).

•  Since the halogen is more electronegative than carbon, the C—X bond breaks heterolytically and X- leaves.

Reactions of Alkyl halides (A) Substitution Reactions

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Reactions of Alkyl halides

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Alkynes

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  (1) Parent name is alkyne i.e. change the -ane to -yne.

 Choose the longest continuous chain containing the triple bond as the basis for the parent name.

 The position of the triple bond takes the lowest possible number.

IUPAC nomenclature

Nomenclature of alkynes

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Write the IUPAC name of the following compounds

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41 Chapter 9 41

Bond Lengths •  Triple bonds are shorter than double or single

bonds because of the two pi overlapping orbitals.

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Acidity Table

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Preparation of Alkynes

RX must be 1o

Pent-2-yne Propyne

NaNH2: Sodium amide

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Reactions of Alkynes Enol Keto

Reactions of Alkynes

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Keto–Enol Tautomerism

•  Tautomers: are compounds whose structures differ markedly in arrangement of atoms, but which exist in easy and rapid equilibrium.1

•  Enols are not stable and they isomerize to the corresponding aldehyde or ketone in a process known as keto-enol tautomerism.

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Reactions as acids

Reactions of Alkynes

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Reduction to Alkenes

cis-But-2-ene trans-But-2-ene

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Homework

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Homework


Alcohols

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51 Chapter 10 51

Structure of Water and Methanol

•  Oxygen is sp3 hybridized and tetrahedral. •  The H—O—H angle in water is 104.5°. •  The C—O—H angle in methyl alcohol is 108.9°.

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Physical Properties

•  Alcohols have high boiling points due to hydrogen bonding between molecules.

•  Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.

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53 Chapter 10 53

Classification of Alcohols

•  Primary: carbon with —OH is bonded to one other carbon.

•  Secondary: carbon with —OH is bonded to two other carbons.

•  Tertiary: carbon with —OH is bonded to three other carbons.

•  Aromatic (phenol): —OH is bonded to a benzene ring.

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Examples of Classifications

C H 3 C C H 3

C H 3 O H *

C H 3 C H O H

C H 2 C H 3 *

C H 3 C H C H 3

C H 2 O H *

Primary alcohol Secondary alcohol

Tertiary alcohol

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  (1) Parent name is alkanol

  Choose the longest continuous chain containing the hydroxy group.

  Numbering begins at one end so as to give the hydroxy group the lowest possible number.

  Alcohols with two –OH groups are called diols and Alcohols with three –OH groups are called triols.

IUPAC nomenclature

Nomenclature of alcohols

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Multifunctional Compounds •  The functional group with the highest priority

determines the parent name.

aldehyde > ketone > alcohol > alkene > alkyne

Naming Priority:

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Examples of Nomenclature

2-Methyl-1-propanol 2-Methylpropan-1-ol

2-Methyl-2-propanol 2-Methylpropan-2-ol

2-Butanol Butan-2-ol

C H 3 C C H 3

C H 3 O H

C H 3 C H C H 3

C H 2 O H C H 3 C H O H

C H 2 C H 3 3 2 1 1 2 3 4

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4-penten-2-ol pent-4-en-2-ol

C H 2 C H C H 2 C H C H 3 O H

5 4 3 2 1

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Write the IUPAC name of the following compounds

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Lectures 4 Nomenclature for student 2013-2014 BW