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SATURATED HYDROCARBON
Synthesis of alkanes
Hydrogenation of alkenes
An example of addition reaction
Hydrolysis of Grignard reagent
(alkylmagnesium halide)
Wurtz reaction (Reduction of alkyl halide)
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Reaction of Alkanes
Combustion
Halogenation
A reaction where a halogen replaces one or more hydrogen
UNSATURATED HYDROCARBON
Synthesis of alkenes
dehydrogenation of alkanes:
X = Y = H
dehydration of alcohols:
X = H; Y = OH
dehydrohalogenation of alkyl halides:
X = H; Y = Br, Cl
Synthesis of alkenes: elimination reactions
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Dehydrogenation of alkanes
Elimination of molecule H2
limited to industrial synthesis of ethylene, propene
Dehydration of alcohol
Loss of H and OH from adjacent carbons.
Acid catalyst is necessary.
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Regioselectivity in alcohol dehydration
A reaction that can proceed in more than one
direction, but in which one direction predominates,
is said to be regioselective.
Zaitsev Rule
When elimination can occur in more than one
direction, the principal alkene is the one formed
by loss of H from the carbon having the
fewest hydrogens
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Dehydrohalogenation of alkyl halides
Loss of H and halogen (X) from an alkyl halide
In the presence of strong base in solvent likewise
Reactions of alkenes
Primarily reactions involve the double bond
The key reaction of double bond is addition reaction
(Breaking the bond and adding something to each carbon)
The major alkene reactions include additions of hydrogen
(H2),halogen ( CI2 or Br2), water (HOH) or hydrogen
halides (HBr or HCI)
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Hydrogenation Addition of H2
Addition of a molecule of H2
Results in the formation of an alkane
Usually requires heat, pressure and a catalyst like Pt, Pd or Ni
Hydration: Addition of H2O
The addition of water to an alkene
produces an alcohol
One carbon get an H, the other an OH
The reaction requires a small amount of acid to be present
to work.
Markonikovs Rule
The carbon with the most carbon-hydrogen bonds initially,
will recieve the hydrogen.
Only valid if the alkenes is unsymmetrical
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Always look for the carbon with the most hydrogen. It
will get the additional H.
Hydrohalogenation
Addition of HX to an alkene
HX HF, HCI, HBr, HI
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It follows Markonikovs rule where the H ends up on the
carbon with the most hydrogen to start with
Halogenation: Addition of X2
The addition of halogen to an alkene
produces a haloalkane or alkyl halide
Synthesis of alkynes
Dehydrohalogenation of dihaloalkane
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i. Geminal dihalide
Dehydrohalogenation of dihaloalkane
ii. Vicinal dihalide
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Reaction of alkynes
Hydrogenation of Alkynes
Hydrohalogenation of alkynes
Follow Markonikovs rule
Alkynes are slightly less reactive than alkenes
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Example
Hydration of alkynes
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Example
Synthesis of Alcohols
Alcohols can be prepared by the hydration of alkenes or by the reduction of aldehydes,
ketones, acids, and esters.
Hydration of alkenes
The elements of water can be added to the double-bonded carbons of an alkene in either a
Markovnikov's or an anti-Markovnikov's manner. As shown in the following figure, a
hydrogen ion catalyzes the Markovnikov's addition.
The anti-Markovnikov's addition results from a hydroboration-oxidation reaction.
Reduction of aldehydes and ketones
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An aldehyde has a structural formula of
while the structural formula of a ketone is
In these formulas, the R or R group may be either an aliphatic or aromatic group. In a
ketone, the R and R groups may represent the same group or different groups. These types
of compounds are best reduced by complex metal hydrides, such as lithium aluminum
hydride (LiAlH4) or sodium borohydride (NaBH4).
Following are two examples of complex metal reductions:
Lithium aluminum hydride is a very strong reducing agent that will reduce many functional
groups in addition to aldehydes and ketones. Sodium borohydride is a much weaker
reducing agent that basically will reduce only aldehydes and ketones toalcohols.
You can also catalytically reduce aldehydes and ketones to produce 1° and 2° alcohols.
Reduction conditions are very similar to those used to reduce alkene double bonds. If amolecule possesses both a double bond and an aldehyde or ketone functional group,
reduction of the aldehyde or ketone group is best carried out using sodium borohydride. The
reduction of cyclohexanone by hydrogen gas with a platinum catalyst produces cyclohexanol
in good yield.
Reduction of carboxylic acids
The reduction of a carboxylic acid:
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leads to the formation of a primary alcohol:
This reduction requires a very strong reducing agent, and lithium aluminum hydride is the
standard choice.
Diborane, B2H6, also reduces carboxylic acids to alcohols.
Catalytic hydrogenation gives very poor yields and is not usually used for this type of
reaction.
Reduction of esters
Esters, like carboxylic acids, are normally reduced with lithium aluminum hydride. In these
reactions, two alcohols are formed. An example is the reduction of methyl benzoate to
benzyl alcohol and methanol.
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Grignard reaction with aldehydes and ketones
The Grignard reaction is the only simple method available that is capable of producing
primary, secondary, and tertiary alcohols. To produce a primary alcohol, the Grignard
reagent is reacted with formaldehyde.
Reacting a Grignard reagent with any other aldehyde will lead to a secondary alcohol.
Finally, reacting a Grignard reagent with a ketone will generate a tertiary alcohol.
Synthesis of Aldehydes and ketones
Oxidation of 10 Alcohol
General equation :
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Oxidation of primary alcohols to aldehyde using pyridium chlorochromate (PCC) in
anhydrous media such as dichloromethane.
ii) Hydration of Alkynes
General equation :
Keto- Enol Tautomerism
The name enol is derived from the IUPAC designation of it as both an alkene (-en-) and
alcohol (-ol).
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Keto and enol forms are examples of tautomers, constitutional isomers in equilibrium
with each other that differ in the location of hydrogen atom and a double relative to a
heteroatom, most often O, S, or N.
This type of isomerism is called tautomerism.
O OH
|| |
CH3-C-CH3 CH3 -C = CH2
acetone acetone
(keto form) (enol form)
Ozonolysis of Alkenes
General equation :
Hydrolysis of Gem Halides
To produce aromatic aldehyde
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Reaction and Synthesis of Carboxylic Acid
The classic synthesis is the Fischer esterification, which involves treating a carboxylic acid
with an alcohol in the presence of a dehydrating agent:
RCO2H + R'OH RCO2R' + H2O
Ester hydrolysis
Acid-catalyzed reaction
Reaction of esters
Soap formation (Saponification)
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Reaction Of Amines
Tertiary Amines have no hydrogen atom and three alkyl or aryl groups attached to the
nitrogen
ALIPHATIC: trimethylamine, ,
ethyldimethylamine, ,
diethylmethylamine, ,
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Reaction Of Amides
The CLASSIFICATION system for alcohols, amines and amides
Functionalgroup of the
homologous
series
PRIMARY SECONDARY TERTIARY Comments
ALCOHOLS
Phenols are
NOT
classified in
this way. The
ease of
oxidation
and nature
of product isaffected by
the class of
the alcohol
examples of
alcohols butan-1-ol
propan-2-ol 2-methyl-
propan-2-ol
examples of
alcohols
AMINES
There are
prim/sec/ter
t aliphatic
(alkyl) or
aromatic
(aryl)
amines. See
also Note 3.
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