Organic chemistry: Hydrocarbons, Alkyl Halides and alcohols

Organic Chemistry II

Hydrocarbons, Alkyl Halides, and Alcohols

Indra Yudhipratama

Outline Alkanes

Combustion Free Radical Reaction

Alkenes and Alkynes Elimination and Addition Polymerisation

Alkyl Halides Substitution Elimination

Alcohols Elimination (Dehydration) Oxidation

Aliphatic Hydrocarbons The aliphatic hydrocarbons alkanes, alkenes, and alkynesAlkanes Physical Characteristics

Alkanes The reactions

Combustion reaction The alkanes reacts with oxygen

Incomplete combustion

Complete combustion

Cracking From long chain alkanes into the shorter chains. E.g.:

Aliphatic Hydrocarbons Alkanes Free Radical Reaction Free Radical: an atom or group of atoms with an unpaired electron Three main steps:

Homolytic Fission

Minor Product

Initiation:

Propagation:

Termination:

Cl Clh v

Cl + Cl

ClCH3 H CH3 + ClH

ClCH3 Cl Cl CH3 Cl +

Cl Cl Cl Cl

CH3 Cl CH3 Cl

CH3CH3 CH3CH3

Alkenes and alkynes How to prepare alkenes?

Dehydration of alcohols

Dehydrohalogenation of alkyl halides

The reaction is called elimination reaction. Alkenes could be prepared from cracking reaction

Cl

S tro n g B a se (E .g . K O H )

in C H 3 O Hmajor product

OH

C o n c d H 2 S O 4

1 7 0 oC

Alkenes and alkynes The Reactions of Alkenes

Addition Reaction All the reagents attacks highly electron density (the Alkenes) The Reaction is called Electrophile (love electrons) Addition

Reacts with hydrogen

Reacts with Halogens

H 2 , N i c a ta lys t

B r 2

C C l4 Br

Br

Alkenes Reaction with Halogens (The Mechanisms)

Br Br

+Br

+ + Br-

Br+ + Br

- Br Br

Alkenes

Reaction with Hydrogen Halides

Via:

Which one is the major product?

HBrH

Br

Br

H+

H BrH

H

+

2 possible sites to attack H

HBr

H

Br

H

BrH

Br

Alkenes The stability of intermediate would determine the major product.

The Stability series of carbocationThe intermediate (Carbocation)

H BrH

H

+

2 possible sites to attack H

> > > CH3

less stable intermediate

Alkenes The Reaction with Steam

Via:

2 Possible products.Which one is the major product?Et

H2O

300 oC Et

HO

+

Et

OH

Et

HO

H

Et

H

+

Et

H

the major product most stable carbocation

Et

H

OH

H

Et OH

the major product

Alkenes Reactions with basic permanganate(VII) ions

Oxidation with cold basic permanganate(VII) ions

Oxidation with hot basic permanganate (VII) ions

Polymerisation

CH3CH3

K M nO 4 , O H -, H 2 O

C o ld CH3CH3

OH

OH

pentane-2,3-diol

CH3CH3

K M n O 4 , O H -, H 2 O

H e a tCH3

O

OHCH3

O

OH+

propanoic acidethanoic acid

Alkenes and Alkynes How to prepare alkynes?

Further dehydrohalogenation dialkyl halide

Mainly, alkynes reacts the same way as alkenes. Alkynes as acids

CH2CH3

1 . B r 2 , C C l4

2 . N a N H 2

CHCH3

CHCH3

N a N H 2

N H 3 (a q )C

-CH3 Na

+ + NH3

Alkenes and Alkynes Hydration of Alkynes

1 eq. H2 would make 2 possible product

R R1

H 2

L ind la r 's C a ta lys t R R1

R R1

R

R1

N a

N H 3 (a q )

Alkyl Halides (Haloalkanes) How to prepare it?

Free radical reaction from alkanes

Addition reaction from alkenes with hydrogen halides or halogens

R XWhere X is Halogens

CH3 CH3

X 2

hvCH3

X

CH2 CH2

X

XX 2CH2 CH2

CH3

X

H X

Alkyl Halides The Reaction The Substitution Reaction (SN1 and SN2)

What does it mean?

SN1

Nucleophilic substitution reactionunimolecular

SN2

Nucleophilic substitution reaction bimolecular

Alkyl HalidesThe Terms What does nucleophilic mean? (Nucleo Nucleus, philic love or

like) Why is it called substitution reaction? Look closely at the reaction

below

How about unimolecular and bimolecular? Related to the mechanism and it is determined by its spatial

arrangement

CH3

Br

O H - CH3

OH

Slide 18 of 69 Copyright © 2011 Pearson Canada Inc.

General Chemistry: Chapter 27

Introduction to Nucleophilic Substitution Reactions

The SN1 and SN2 Mechanisms of Nucleophilic Substitution Reactions

rate = k[OH-][CH3Cl]

HO:::

ClCH3 ::: k1

k-1

HO::

ClCH3 :::

:- -

Reaction profile for an SN2 reactionFIGURE 27-1

Inversion of configuration in the SN2 mechanism

FIGURE 27-2

The SN1 Mechanism

Reaction profile for the reaction between t-butyl bromide and water

FIGURE 27-4

Formation of a racemic mixture in an SN1 reaction

Slide 25 of 69 Copyright © 2011 Pearson Canada Inc.

General Chemistry: Chapter 27

Relative rates of reaction

SN1 reaction

SN2 reaction

A Summary of SN1 and SN2 Reactions

Alkyl HalidesAnother Reactions Reaction with AgNO3

R – X + AgNO3 R+ NO3- + AgX

AgX insoluble precipitate Elimination CH3

CH3Cl

S t ro ng B a se (E .g . K O H )

in C H 3 O H

CH3

CH3

KOH + CH3OH KCH3O + H2O

CH3

CH3Cl

HCH3 O

-CH3

CH3

Alcohols Main Features: Alcohol has relatively higher b.p. compare to the

others organic compound Classification of organic compound

Primary (1o) Alcohole.g.

Secondary (2o) Alcohol e.g.

Tertiary (3o) alcohole.g.

R OH

R1

R

OH

R2

R

R1

OH

CH3 OH

CH3CH3

OH

CH3 CH3

OHCH3

OH

R

R1

R2

AlcoholsHow to prepare it? Substitution reaction of alkyl halide with base.

Reaction of alkene with steam

Fermentation

CH3

Br O H -

CH3

OH

CH2

CH3

H5C2

H 3 O + , 3 0 0 oCCH3

CH3

H5C2 OH

Predict whether this reaction is SN1 or SN2.

AlcoholsThe reactions involve alcohol Combustion (e.g. ethanol)

Substitution

R1

R2

OHR X -

R1

R2

XR

Predict whether this reaction is SN1 or SN2 and identify which one is the leaving group

Alcohols Reaction with sodium (identification) (e.g. ethanol)

Reaction with alkaline aqueous iodine (identification CH3CH(OH)- group)

OHI2

NaOH(aq)

O I2

NaOH(aq)I3C

OI2

NaOH(aq) O

O

+ CHI3

Alcohols (The Reactions) Dehydration into alkene

Via:

OHConc. H2SO4

170 oC

OHH

OS

O

OOH

HOH

HO

S

O

OOH

Alcohols (The Reactions) Oxidation (could be used for identification primary, secondary, or

tertiary)

Ester formation

CH3 OH

CH3 CH3

OH

CH3 CH3

OHCH3

[O ]

[O ]

[O ]

CH3 O

CH3 CH3

O

No Reaction

[O ] CH3 O

OH

[O ]No Reaction

CH3 OHCH3 O

OH

+H 3 O +

CH3

O

O CH3Alcohol Carboxylic Acid Ester