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2014-1435

Dr Nahed Elsayed

Learning ObjectivesLearning Objectives

Chapter five discusses the following topics and by the end of this chapter the students Chapter five discusses the following topics and by the end of this chapter the students will: will:

Recognize the structure and classes of alkyl halidesRecognize the structure and classes of alkyl halides

Know the common names and understand the IUPAC rules for nomenclature ofKnow the common names and understand the IUPAC rules for nomenclature of halo compoundshalo compounds

Understand the physical properties of halo compounds (solubility and boiling points)Understand the physical properties of halo compounds (solubility and boiling points)

Know the different methods used in preparation of halo compoundsKnow the different methods used in preparation of halo compounds

Know the reactions of halo compounds; nucleophilic substitution, elimination, Know the reactions of halo compounds; nucleophilic substitution, elimination, reduction reactions of Grignard reagents and know the previously disused methods of reduction reactions of Grignard reagents and know the previously disused methods of reducing alkyl halides (Chapter-1)reducing alkyl halides (Chapter-1)

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Structure Of Alkyl HalidesStructure Of Alkyl HalidesAlkyl halides: Alkyl halides: are compoundsare compounds contain the contain the C-XC-X bondbond where X is a where X is a halogen halogen (F,Cl,Br or I)(F,Cl,Br or I)

Classes of Alkyl halides:Classes of Alkyl halides: They are classified according to the type of carbon atom bearing the They are classified according to the type of carbon atom bearing the

halogen intohalogen into: : Primary alkyl halide CHPrimary alkyl halide CH33-X and R-CH-X and R-CH22-X-X

Secondary alkyl halide (R)Secondary alkyl halide (R)22-CH-X-CH-X

Tertiary alkyl halideTertiary alkyl halide (R) (R)33-C-X -C-X

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Classes of hydrocarbon group:Classes of hydrocarbon group: Alkyl halides( R-X) has a halogen atom bonded to one sp3 hybrid

C atom Allylic halides has a halogen atom bonded to one sp3 hybrid

C atom but in third position of allylic group Vinylic halides has a halogen atom bonded to one sp2 hybrid

C atom Benzylic halides has a halogen atom bonded to Carbon that

one atom away from aromatic ring Aryl halides has a halogen atom bonded directly to an

aromatic ring

5145 Chem 5

3-Allyl halides

C=C-C- X

CH2=CHCH2ClAllyl chloride

3-Chloro-1-propene

Cl

3-Chlorocyclopentene

4-Benzylic halides: Ar-C-X

CH2Cl

Benzyl Chloride

Br

2-Vinylic halides

Bromocyclohexene

C=C-X

CH2=CHBr Vinyl bromideBromoethene

5-Aryl halides: Ar-X (X directly attached to )

ClBr

CLCH3

Chlorobenzene p-Bromo toluene

Notice

Nomenclature OF Alkyl Nomenclature OF Alkyl halideshalidesIUPAC names derived from the names of parent organic compound (alkane derived from the names of parent organic compound (alkane

or alkene or alkyne or alcohol or aldehydes and so on) with a prefix indicating or alkene or alkyne or alcohol or aldehydes and so on) with a prefix indicating halogens andhalogens and their positions. their positions. Common namesCommon names derived from the corresponding alkyl group followed by derived from the corresponding alkyl group followed by the name of halogen atom.the name of halogen atom.

CH3-Cl CH3-CH2-Br (CH3)2-CH-FCommonCommon Methyl Chloride Ethyl bromide Isopropyl Methyl Chloride Ethyl bromide Isopropyl fluoridefluorideIUPAC IUPAC Chloromethane Bromoethane 2-Chloromethane Bromoethane 2-FluoropropaneFluoropropaneClass Class 1°1° 1° 2° 1° 2°

CommonCommon Cyclohexyl Iodide Cyclohexyl Iodide tt-Butyl bromide Methylcyclopentyl -Butyl bromide Methylcyclopentyl chloridechloride IUPACIUPAC Iodocyclohexane 2-Bromo-2- methylpropane 1-Chloro-1-methyl cyclopentaneIodocyclohexane 2-Bromo-2- methylpropane 1-Chloro-1-methyl cyclopentane

Class Class 2° 3 ° 3 °2° 3 ° 3 °

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ClBr

3-Chlorocyclopentene

Bromocyclohexene

Physical PropertiesPhysical Properties

SolubilitySolubility :: All organic halides are All organic halides are insoluble insoluble in water and soluble in common organic in water and soluble in common organic solvents.solvents.

Boiling point :Boiling point : The boiling points increases with increasing in molecular weights. The boiling points increases with increasing in molecular weights.

Therefore, the Therefore, the boiling points increasesboiling points increases in the order in the order F < Cl < Br < I. F < Cl < Br < I.

In an alkyl halide, the halogen is more electronegative that carbon

Alkyl halides have higher melting points Alkyl halides have higher melting points than alkanes, alkenes, alkynes because of than alkanes, alkenes, alkynes because of 1. Polarity1. Polarity2. Molecular weight2. Molecular weight

Preparation Of Halocompounds

1- 1- Direct Halogenation Of HydrocarbonsDirect Halogenation Of Hydrocarbons

a)a)Halogenation of alkanesHalogenation of alkanes

b)b) Halogenation of alkenesHalogenation of alkenes

c) Halogenation of alkynesc) Halogenation of alkynes

d) Halogenation of alkyl benzened) Halogenation of alkyl benzene

CH2R+ X2

UV or heat

CHXR

+ HX

CH2RCH2RFeX3

+

XXp-Isomer o-Isomer

2- Halogenation Of Alcohols2- Halogenation Of Alcohols

R OH + HX or SOX2 , PX3, PX5 Heat

R XZnCl2

CH3 OH PCl3 / ZnCl2

heat

CH3 Cl + OH2

OH

SOCl2

Cl

+ SO2 + ClHZnCl2

OH

CH3

PBr3

ZnCl2

Br

CH3

OH

CH3

CH3

CH3conc HCl

Cl

CH3

CH3

CH3

+ P(OH)3

Reactions of Organic HalidesReactions of Organic Halides1- Nucleophilic Substitution1- Nucleophilic Substitution ReactionsReactions

Nu= OH, OR, OCOR, NH2, RNH, SH, SR, CN, X, HC C, RC C,

Br INaI / Acetone

2- Elimination2- Elimination Reactions:Reactions: Alkyl halides can lose HX molecule to give an alkenAlkyl halides can lose HX molecule to give an alken If the haloalkane is unsymmetrical (e.g. 2-bromobutane or 2-If the haloalkane is unsymmetrical (e.g. 2-bromobutane or 2-bromopentane) a mixture of isomeric alkene products is obtained.bromopentane) a mixture of isomeric alkene products is obtained.

BrConc. KOH Or C2H5O Na Or PhO Na

EtOH / Heat+

2-Butene Major

1-Butene Minor

C C

XX

Strong base

- 2 HXC C

Br

Br

1,2-dihaloalkane

Excess NaNH2

- 2HBr

Br

Br

Br

KOH/ alcohol

heat

NaNH2

heat

3) Formation of Grignard reagent and its 3) Formation of Grignard reagent and its reactionsreactions

Reactions of Grignard reagentReactions of Grignard reagent

R MgX

H2O

R'OH

HC CH

R H

R H

R H

+

+

+

Mg(OH)X

Mg(OR')X

Mg(HC C)X

4- Reduction of alkyl halides4- Reduction of alkyl halidesa) Reduction by Zinc metal and acids or by a) Reduction by Zinc metal and acids or by metal hydridesmetal hydrides

CH3CH2CH2Br + ZnH

CH3CH2CH3 + ZnBr2

CH3CH2CH2CH2Br1) LiAlH4 / ether

2) H3OCH3CH2CH2CH3

b) Reduction by sodium metal (coupling reaction)b) Reduction by sodium metal (coupling reaction)

c) Reduction using lithium dialkyl cupratec) Reduction using lithium dialkyl cuprate

Questions?