SCH 4U Organic Day 4
1.3 Alkane, alkene, alkyne reactions
Assignment:
Page 27 # 1-3
30 # 4-7
Lab 1.3 page 84
Learning Check Alk9
Select all correct names for each structure:
Cl
1. Chlorocyclohexane
2. Chlorobenzene
3. 1-chlorobenzene
CH 3
CH 3
1. Meta-methyltoluene
2. Meta-dimethylbenzene
3. 1,3-dimethylbenzene
Solution Alk9
Select the names for each structure:
Cl
2. Chlorobenzene
CH3
1. Meta-methyltoluene
2. Meta-dimethylbenzene
3. 1,3-dimethylbenzene
CH 3
Learning Check Alk10
Write the structural formulas for each of the
following:
A. 1,3-dichlorobenzene
B. Ortho-chlorotoluene
Solution Alk10
Write the structural formulas for each of the
Cl
following:
A. 1,3-dichlorobenzene
Cl
CH 3
B. Ortho-chlorotoluene
Cl
ALKANE REACTIONS
Reactions of Alkanes
Combustion
CH4
+ 2O
2
CO2
+ 2 H O + energy
2
Dehydrogenation
RCH2
High Temp.
catalyst
CH2R
RHC
CHR
alkene
+
H
H
Halogenation – radical substitution reactions
light or heat
+ Br2
Br
+ HBr
Combustion
Reactions
5. Combustion
Reactions
•
•
Combustion reactions
occur when a hydrocarbon
reacts with oxygen gas.
The 3 requirements for
Combustion in the “fire
triangle” are:
1) A Fuel (hydrocarbon)
2) Oxygen to burn it with
3) Heat to ignite the
reaction (spark)
Combustion Reactions
•
In general:
CxHy + O2 à CO2 + H2O
•
Products in combustion are
carbon dioxide and water
(although incomplete combustion
does cause some byproducts
like carbon monoxide)
Combustion is used to heat
homes and run automobiles
(octane, as in gasoline, is C 8H18)
•
Combustion
Reactions
Edgar Allen Poe's
drooping eyes and
mouth are potential
signs of CO
poisoning.
www-cm ls.llnl.gov/?url=science_and_technology...
Alkane Substitution Reactions
P Organic reactions with alkanes are much
slower than inorganic reactions (or alkene
reactions)
P Strong covalent bonds must be broken for
organic reactions to occur
P Replacing a hydrogen atom with some other
atom (or atoms) is a substitution reaction
P Alkyl halides are usually produced
Halogenation
H
H
H
C
C
H
H
H
+
Heat or Light
D or hv
Br2
H
Ethane
C
Heat or Light
D or hv
H
H
Methane
+
H
C
C
H
H
Br
+
HBr
Bromoethane
H
H
H
Cl2
H
H
C
Cl
+
HCl
H
chloromethane
CH2Cl2 and CHCl3
may be observed
Substitution R eaction – a reaction in which part
of a small reacting molecule replaces an atom or a
group of atoms on the organic molecule (usually very slowly)
BENZENE REACTIONS
Benzene Substitution Reactions
P Benzene does not contain double bonds due
to delocalization of electrons
P Strong covalent bonds must be broken for
substitution reactions to occur in benzene
P Slow substitution reactions can occur but no
addition reactions occur with benzene
HALOGENATION
Cl2 , AlCl3
Cl
Br2, FeBr3
Br
Professor Charles Friedel
and Professor James Crafts
Br
Br
Br FeBr3
H
+
FeBr4
Reactions on Aromatic Rings: Substitution
• Aromatic Substitution
NO 2
H 2SO 4
reaction – Aromatic
+ H 2O
+ HNO 3
compound loses a
hydrogen atom and
another atom or group
takes its place.
NO 2
NO 2
NO 2
• It is possible for
NO 2
substitution to occur in
NO 2
more than one place on
NO 2
ortho-Dinitrobenzene para-Dinitrobenzene meta-Dinitrobenzene
the ring.
ALKENE REACTIONS
P The double covalent bond in an alkene is
much easier to break than the single C-C
bond
P Addition reactions add across a double bond
P Addition reactions occur much faster than
substitution reactions
Addition of Bromine
to an Alkene
Br
R
CH CH
R
+
Br2
CCl4
or CH2Cl2
R
CH CH
Br
R
Bromine addition and Oxidation Reactions
Hydrogenation of Alkenes
Pt, Pd,
R
CH CH R
+
H2
or Ni
R
CH CH R
H
Also PtO2 -- sometimes Ru, Rh, or Re
H
Markovnikov’s Rule
P Alkene addition reaction with H-X
P The halogen (X)
P H more often adds to the Carbon that
has more H to begin with
MARKOVNIKOV RULE
PREDICTING THE MAJOR PRODUCT
When adding HX to a double bond,
the hydrogen of HX goes to the carbon
which already has the most hydrogens
CH 2
+ HCl
CH 3
Cl
major
product
..... conversely, the anion X adds to the
most highly substituted carbon
( the carbon with most alkyl groups attached).
AN “EMPIRICAL” RULE
Markovnikoff formulated his rule by observing
the results of hundreds of reactions that he
performed.
EMPIRICAL = DETERMINED BY OBSERVATION
He had no idea why the reaction worked this
way, only that as a general rule it did give the
stated result.
SOME ADDITIONAL EXAMPLES
only major product is shown
CH3
+ HCl
CH2
+ HCl
CH CH2
+ HCl
CH3
Cl
CH3
Cl
CH CH3
Cl
Addition of Water to an Alkene
R
CH CH2
+
H2O
H2SO4
R
CH CH2 H
OH
an alcohol
MARKOVNIKOFF ADDITION
( HYDRATION REACTIONS, H 2 SO4 + H2 O )
CH 3
CH 3
H 2SO4
+ H 2O
OH
CH 3
CH 2
H 2SO4
+ H 2O
H 2SO4
OH
CH CH 2
CH CH 3
+ H 2O
OH
ALKYNE REACTIONS
–
Alkene Hydrogenation
C
H
C
H
Pt or Pd - catalyst
solvent, pressure
C H
C H
Double Hydrogenation for Alkynes
C
C
2X
H
H
Pt - catalyst
solvent, pressure
H C H
H C H
Alkynes are more reactive in halogenation reactions than
alkenes and can undergo 2 addition reactions
Combustion
Alkynes are high energy compounds
H
C
C H
+
2.5 O 2
“Acetylene” (Welding gas)
2 CO 2
+ H 2O
Addition Polymers
Addition Polymers
H
H
C
C
H
H
C
C
H
H
catalyst
H
H
ethylene
polyethylene
a macromolecule with very high molecular
weight
Polymerization of propene
H
CH3
catalyst
C
C
three different forms of “polypropylene”
syndiotactic, isotactic and atactic
H
H
CH3
CH3
CH3
C H3
isotactic
CH3
CH3
CH3
CH3
syndiotactic