Properties of Alkenes and Alkynes
Chemical Properties
Undergo combustion as do alkanes .
Alkenes and Alkenes-reactive at the multiple bond.
Physical Properties
Nonpolar and insoluble in water as are alkanes.
Nonpolar, therefore Boiling points depend on size and shape.
Alkenes may display cis-trans isomerism.
Chemical Reactions of Unsaturated Compounds
Chemical Reactions of Alkenes
Structure of the Double Bond in Alkenes
C C
The two components of the double bond
are pictured the same, but one of the
bonds (the π bond) is actually weaker than
the other.
The characteristic reaction of alkenes is an ADDITION REACTION.
Chemical Reactions of Alkenes
+
“A” and “B” are not necessarily single atoms.
“A” and “B” are added to the structural and
molecular formula.
WHAT ARE “A” AND “B” ? H-H Hydrogenation X-X Halogenation H-X Hydrohalogenation H-OH Hydration
C C C C
A
A"catalyst"
B
B
Chemical Reactions of Alkenes
C C
A B
C C C C
A
A"catalyst"
B
B
C C
A B
C C C CH H
H HNi or Pt catalyst
HC
HC
H
HH C
H
C
H
H
H HH2, Ni or Pt catalyst
H3CC
H3CC
CH3
CH2CH3
H3C C
CH3
C
CH2CH3
CH3
H HH2, Ni or Pt catalyst
Catalytic Hydrogenation
Specific Examples
alkenes alkanes
+
Specific Examples
Catalytic Hydrogenation
C C C CH H
H HNi or Pt catalyst
HC
HC
H
HH C
H
C
H
H
H HH2, Ni or Pt catalyst
H3CC
H3CC
CH3
CH2CH3
H3C C
CH3
C
CH2CH3
CH3
H HH2, Ni or Pt catalyst
ethene ethane
C2H4 C2H6
2,3-dimethyl-2-pentene 2,3-dimethylpentane
C7H14
C7H16
+
Halogenation - Synthesis of Alkyl Halides
C C C CX X
X XDark, no catalyst
HC
HC
H
HH C
H
C
H
H
Cl ClCl2, no catalyst
H3CC
H3CC
H
CH2CH3
H3C C
CH3
C
CH2CH3
H
Cl ClCl2, no catalyst
General Reaction
Specific Examplesalkenes alkylhalides
+
Halogenation - Synthesis of Alkyl Halides
C C C CX X
X XDark, no catalyst
HC
HC
H
HH C
H
C
H
H
Cl ClCl2, no catalyst
H3CC
H3CC
H
CH2CH3
H3C C
CH3
C
CH2CH3
H
Cl ClCl2, no catalyst
General Reaction
Specific Examples
ethene 1,2-dichloroethane
2-methyl-2-pentene 2,3-dichloro-2-methylpentane
C2H4 C2H4Cl2
C6H12
C6H12Cl2
+
Addition of Bromine (Br2)
CH3 CH CH CH2 CH3 CH3 CH CH CH2 CH3
Br BrBr2no catalyst
Br2no catalyst
BrBr
Br2no catalyst No reaction
Chemical Reactions of Alkenes
Addition of Bromine (Br2)
Alkane Alkene Alkane +
Br2
Alkyl Bromide Br2 in
CCl4
Addition of Bromine (Br2)
The result can be quantitated.
Chemical Reactions of Alkenes
The characteristic reaction of alkenes is an ADDITION REACTION.
Chemical Reactions of Alkenes
+
“A” and “B” are not necessarily single atoms.
“A” and “B” are added to the structural and
molecular formula.
WHAT ARE “A” AND “B” ? H-H Hydrogenation X-X Halogenation H-X Hydrohalogenation H-OH Hydration
C C C C
A
A"catalyst"
B
B
Hydrohalogenation-Synthesis of Alkyl halides
C C C CH X
H X
or
C C
X H
+
H3C CH CH CH3H Cl
H3C CH CH CH3
H Cl
H3C CH CH CH3
Cl H
or
Specific Example:
2-chlorobutane
2-chlorobutane
C4H9Cl
C4H8
2-butene
In some cases only one product can be formed.
In some cases two isomeric products are possible:
2-chloropropane
1-chloropropane
propene ?
( )
( )C3H6
C3H7Cl
H3C CH CH2H Cl
H3C CH CH2
H Cl
H3C CH CH2
Cl Hor
H3C CH2 CH2
Cl
H3C CH CH3
Cl
MARKOVINIKOV’S RULE- When adding H-X or H-OH (H2O) to alkenes with different number of groups attached to the double bonds, the “H” portion of the reagent adds to the carbon that has the greater number of hydrogen atoms in the reactant molecule.
H-Cl H-Br H-OH
Major product
1-chloropropane
2-chloropropane
propene
H3C CH CH2H Cl
H3C CH CH2
H Cl
H3C CH CH2
Cl Hor
H3C CH2 CH2
Cl
H3C CH CH3
Cl
What is the result if two isomeric products are possible ??
2-chloropropane
1-chloropropane
propene ?
( )
( )C3H6
C3H7Cl
H3C CH CH2H Cl
H3C CH CH2
H Cl
H3C CH CH2
Cl Hor
H3C CH2 CH2
Cl
H3C CH CH3
Cl
Major product
Hydration of Alkenes-Synthesis of Alcohols
C C C CH OH
H OH
or
C C
HO H
+
H3CC
H3CCCH3
CH3
H3C C
CH3
C
CH3
CH3H OH
H OH
or
H3C C
CH3
C
CH3
CH3
HO H
+
alcoholsalkenes
2,3-dimethyl-2-butene2,3-dimethyl-2-butanol
C6H12
C6H14O
In some cases Markovnikov's rule is not needed.
Hydration of Alkenes
H3CC
H3CCH
CH3
H3C C
CH3
C
CH3
HH OH
H OH
or
H3C C
CH3
C
CH3
H
HO H
+ H3C CH
CH3
CH CH3
OH
H3C C
CH3
CH2 CH3
HO
Major product
2-methyl-2-butene
3-methyl-2-butanol
2-methyl-2-butanol
C5H10
C5H12O
HHO
*
*
AlkynesThe triple bond consists of two π components
and one σ component.
C C
The characteristic reaction is addition to both of the π bonds.
C C C C2 mol of A-B
A
A B
B
Alkynes
Br Br
2 mol Br2no
catalyst
CH3 C C CH3 CH3 C C CH3
Br Br
Cl H
2 mol HClno
catalyst
CH3 C C H CH3 C C H
Cl H
Markovnikov’s rule may or may not apply.
C4H6 C4H6Br4
C3H4 C3H6Cl2
“Addition” Polymers Overall Reaction:
C=CA
B
X
YC=C
A
B
X
YC=C
A
B
X
YC=C
A
B
X
YC=C
A
B
X
Y
C CA
B
X
YC C
A
B
X
YC C
A
B
X
YC C
A
B
X
YC C
A
B
X
Y
Acid or “initiator”
C CA
B
X
Y( ) n n = number of individual units
CH2 CH2
CH2 CH
CH3
CH2 CH
Monomer Polymer Uses
ethylene
(CH2 CH2 )n
polyethylene
(CH2 CH )n
CH3propylene polypropylene
(CH2 CH )n
styrene polystyrene
bottles, toys, housewares, wire cableinsulation, plastic sheeting
outdoor carpeting, food packagingappliance housings
styrofoam containers, food packaginghairbrush handles, toys
“Addition” Polymers
“Addition” Polymers
CH2 CH
Cl
CH2 CH
CN
CF2 CF2
(CH2 CH )n
Cl
vinyl chloride polyvinylchloride (PVC)
(CH2 CH )n
CN
acrylonitrile polyacylonitrile
(CF2 CF2 )n
tetrafluoroethylene polytetrafluoroethylene
home siding, gutters, flooring, garden hose, PVC tubing
acrylic textile fibers
“Teflon”, mechanical parts, cookware, chemical resistant gaskets
Monomer Polymer Uses
polyacrylonitrile
Aromatic Hydrocarbons
Benzene (C6H6) was discovered in 1825, but a partially correct structure was not proposed until 1865 by August Kekule. The structure consisted of six carbons in a ring joined by alternating single and double bonds.
Physical and chemical evidence indicates that benzene behaves as if all the carbon-carbon bonds are identical. Hence, the fol lowing structural representation is sometimes used:
Resonance in Benzene
Delocalized Bonding in Benzene
sigma bondingsystem
sp2 hybridorbitals
remaining p orbitals
delocalized pi bonding
Aromatic Hydrocarbons-Nomenclature1. Identify the benzene ring in a compound and assign the parent name “benzene”
2. Attach names and location of substituents.
3. For two or more substituents, number the benzene ring starting with one of the substituents to give the lowest combination of numbers to the substituents.
4. Some important monosubstituted benzenes have common names:
Toluene Phenol Aniline Benzoic Acid Benzaldehyde
CH3 OH NH2 COHO
CHO
Aromatic Hydrocarbons-Nomenclature
5. The prefixes ortho (o), meta (m), and para (p) are often used to indicate the relative positions of two substituents in 1,2- , 1,3- , and 1,4- placement on a benzene ring.
1,2-dibromobenzene 1-hydroxy-3-nitrobenzene 1-amino-4-chlorobenzene
Br
Br
OH
NO2
NH2
Cl
ortho-dibromobenzene meta-nitrophenol para-chloroaniline
Aromatic Hydrocarbons-Nomenclature
NH2C
H3C
H3C
H
benzene “amino-”“isopropyl-“
1
23
4
4-isopropyl aminobenzene
orpara isopropyl aniline
Aromatic Hydrocarbons-Nomenclature
4. The benzene ring may be named as a subsituent.
4-chloro-2-methyl-6-phenyl-2-heptene
H3C
C
H3C
CH
HC
Cl
CH2 CH
CH3
The Benzene Ring in Drug Molecules
CH3
CH3OH
AspirinIbuprofen
DextromethorphanCinnamedrine
O OH
O
O
CH3OH
O
CH3
CH2CH
CH3
CH3
HO3S—OH
O2N—OH
Cl—Cl
H—OH
H—OH
H—Cl
Aromatic Hydrocarbons Substitution Reactions
?
H H
H
HH
H Y X +
H H
Y
HH
H+ H X
Y is substituted for H
Aromatic Hydrocarbons Substitution Reactions
H
H
H
H
H
HCl2Fe
H
Cl
H
H
H
H
C6H6 C6H5Cl
H
H
H
H
H
HH2SO4heat
HSO3H
H
H
H
H
C6H6 C6H5SO3H
Aromatic Hydrocarbons Substitution Reactions
H
H
H
H
H
HHNO3heat
HNO2
H
H
H
H
C6H6 C6H5NO2
CH3
H
H
H
H
HHNO3heat
HNO3heat
HNO3heat
CH3
NO2
H
NO2
H
O2N
Tri Nitro Toluene