Organic chemistry: Hydrocarbons, Alkyl Halides and alcohols
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Transcript of 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