32-organic halides

7/24/2019 32-Organic Halides

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Functional Class Nomenclature of Alkyl HalidesFunctional Class Nomenclature of Alkyl Halides

Name the alkyl group and the halogen as

separate words (alkyl + halide)

CH3F CH3CH2CH2CH2CH2Cl

3 2 2 2 3 H

I

-



Nomenclature of Alkyl Halides

CH3Cl CH3CH2FCH3CHI CH3CH2CHBr

3chloromethane fluoroethane2-iodopropane 2-bromobutane

CH3 CH3

3 2 2 2 2 3

Br

2-bromo-5-methylheptane

3 2 2 2 2

CH3

1-chloro-5,5-dimethylhexane

I

Br

CH2CH3

Cl

1-ethyl-2-iodocyclopentane CH3

4-bromo-2-chloro-1-methylcyclohexane



Different Kinds of Alkyl Halides



po e momen

a y a ogen es are po ar

HHHH

CC ClCl –

+

HH = 1.9 D



Boiling point increases with increasing

number of halogens

- °

ompounompoun o ng o no ng o n

CH2Cl2 40°C

3

CCl4 77°C

Even though CCl4 is the only compound in this list without a

di ole moment it has the hi hest boilin oint.

Induced dipole-induced dipole forces are greatest in

4 .

Cl is more polarizable than H.



ro uc on o a y a es

RH + X RX + HX

(2) alcohol + hydrogen halide (nucleophilic substitution)

ROH + HX RX + H2O

NaBr

CH3CH2CH2CH2OH CH3CH2CH2CH2Br 2 4

heat



Thion l chloride

SOCl2 + ROH RCl + HCl + SO2

Phosphorous tribromide

r 3 + r + 3 3



em ca proper es

Elimination reactions



uc eop c su s u on reac ons

SN1 reaction: (mostly tertiary halides)reaction rate depends only on the

concentration of the reactant (first order)

reaction rate depends on the concentration of



SN1 reaction:



SN2 reaction:

HO- + CH3 Br Br CH3HO Br

-CH3

+OH



Reaction of Alcohols with Hydrogen

Halides

RROHOH ++ HHXX RRXX ++ HHOHOH

Hydrogen halide reactivity

HHFF HHClCl HHBr Br HHII

eas reac veeas reac ve most reactivemost reactive



ROH + HX RX + HOH

Reactivity of alcohols:

RCH2OH R2CHOH R3COH



An SN2 reaction proceeds in the direction that allows



Elimination reaction



11



22



Zajcev's ruleZajcev's rule

in hydrogen halide eliminations hydrogen is

eliminated from the carbon atom which had- HCl CH3 CH CH CH3

originally less hydrogen atomsCH3 CH CH2 CH3

but-2-én2-butene

Cl - HCl CH2 CH CH2 CH3

- -- - -- -



-Aryl halides are halides in which the halogen is

.

-Carbon-halogen bonds in aryl halides are

-

bonds in alkyl halides.

- ecause e car on- a ogen on s s ronger,

aryl halides react more slowly than alkyl halidesw en car on- a ogen on rea ng s ra e

determining (SN only under special conditions).



Ph sical Pro erties of Ar l Halides

resemble alkyl halides

all are essentially insoluble in water less polar than alkyl halides

1.7 D 2.2 D



The most important alkyl halidesThe most important alkyl halides

DichloromethaneDichloromethane CHCH22ClCl22

ChloroformChloroform CHClCHCl33 or anic solventsor anic solvents

CarbontetrachlorideCarbontetrachloride CClCCl44

IodoformIodoform CHICHI antise ticantise tic

TetrafluoroethyleneTetrafluoroethylene CFCF22=CF=CF22 TeflonTeflon®®

22 --

a onsa ons

FreonFreon--1212 CFCF22

ClCl22

fire extinguisher fire extinguisher

HalotaneHalotane CFCF33--CHBrClCHBrCl anestheticsanesthetics

,,

now it is banned, can accumulate over the time (!)now it is banned, can accumulate over the time (!)



Dioxins: ol chloro-dibenzo-dioxins

- formerly pesticide, toxic-

- burning PVC



Organic halogen compounds:

-Definition of halogen compounds. Functional group and substitutionnomenclature.

- Production of alkyl halides: halogenation of alkanes, reaction of alcohols

and hydrogen halide, thionyl chloride as well as phosphorous tribromide

(with examples).

- Chemical properties of halogen compounds: 2 main types of nucleophilic

substitution. The most frequent substitution reactions of alkyl halides (with

h droxide c anide halide amine h dro ensul hide alcoholate etc.

nucleophiles). Elimination reactions with examples, Zajcev’s rule.

-,

biological importance: ethylchloride, dichloromethane, vinylchloride,

, , , , - , ,

Dioxins, DDT.

32-organic halides

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