unsaturated hydrocarbons -...
TRANSCRIPT
UnsaturatedHydrocarbons
Chemical Formulas and Unsaturation
C C C C C
C C C C C
H H H H H
H H H H H
H C C C C C H
H H H H H
H H H H H
H C C C C
H H H H
H H
C
H
H
H
H
H
Cn
CnH2n
CnH2n+2
CnH2n+2
Chemical Formulas and Unsaturation
C C C C C
Cn
C C C C C
Cn
C C C C C
Cn
CnH2n
H C C C C C H
H H H
H H H H H
C
C
C C
C
Cn
CnH2n
C
C
C C
C
HH
H
H
H
H H
H
H
H
Chemical Formulas and Unsaturation
Hydrocarbons
SaturatedHydrocarbons
UnsaturatedHydrocarbons
AlkanesCnH2n+2
CycloalkanesCnH2n
(one ring)
AlkenesCnH2n
(one C=C)
AlkynesCnH2n-2
(one C C)
BenzeneC6H6
CnH2n-6
Review of Carbon Bonding Patterns
Lewis Representation of Ethene
C C
H
H
H
HC
H
H C
H
H
N o t e : B o t h o f t h e s e representations picture the two components of the double bond as being identical. This is not the case.
Hybrid Orbitals - Alkanes
Recall that the four orbitals
associated with the bonding in
an alkane or cycloalkane are the result of sp3
hybridizaton.
Hybrid Orbitals - Bonding in Methane
Hybrid Orbitals - Alkenes
In the alkenes a different type of hybridization is used, sp2. The 2s and two of the 2p orbitals about the carbon atom hybridize to form three equivalent sp2 orbitals, leaving a single 2p orbital in an unhybridized state.
Hybrid Orbitals - Alkenes
Covalent Bonding in Ethene
C2H4, ethene, is formed from two sp2 hybridized carbon atoms and four hydrogen atoms:
Lateral overlap of the unhybridized p orbitals, above and below the triangular planes, results in a π bond of the double bond.
Covalent Bonding in Ethene
The two carbons and all four hydrogens all lie within the same plane. The bond angles are all 120º.
Note: Though the two components of the double bond are pictured the same, one of the bonds is actually weaker than the other.
Nomenclature of Alkenes
1. Select the longest carbon chain containing the double bond as the parent chain. Replace the “-ane” ending with “-ene.
2. Number the parent chain beginning at end closest to the double bond beginning with the first carbon in the chain.
3. Locate and name the substituents in alphabetical order.
4. Compounds with two double bonds are called dienes.
5. Cyclic compounds are named as cycloalkenes. Carbons in the double bond are always numbered first. Then the ring is numbered in the direction so as to give the lowest numbers to substituents.
2,3-dimethyl-1-pentene
Alkenes-Nomenclature Practice
2,3-dimethyl-2-hexene
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*
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Alkenes-Nomenclature Practice
2,5-dimethyl-2-heptene 3,3-dimethylcyclopentene
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Isomerism in Alkenes
H2C CH CH2CH2 CH3
H3C CH CH CH2 CH3
H3C CH2 CH CH CH3
Positional Isomerism
1-pentene
2-pentene
????also
2-pentene
Geometric Isomerism (a form of stereoisomerism)
Geometric Isomerism (a form of stereoisomerism)
Isomerism in Alkenes
Exists for the following cases:
C C
X
Y
A
B
A≠B and X≠Y
C C
X
Y
A
B
C C
Y
X
A
B
A result of lack of free rotation around the double bond
X
Isomerism in Alkenes
Isomerism in Alkenes Cis/trans isomers have different physical properties
Isomerism in Alkenes
Cis/trans isomers are not possible for some alkenes.
cis-4-methyl-2-hexene
Alkenes-Nomenclature Practice
trans-5,6-dimethyl-3-heptene
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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
C C C C
A
A"catalyst"
B
B
+
“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 HydrogenationX-X HalogenationH-X HydrohalogenationH-OH Hydration
Chemical Reactions of Alkenes
C C
A B
C C C C
A
A"catalyst"
B
B
C C
A B
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
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
Alkene+
Br2
Br2
Chemical Reactions of Alkenes Addition of Bromine (Br2)
The result can be quantitated.
Hydrohalogenation
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
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
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 already attached.
H-Cl H-Br H-OH
Majorproduct
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
Hydration of Alkenes
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
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
Majorproduct
2-methyl-2-butene
3-methyl-2-butanol
2-methyl-2-butanol
C5H10
C5H12O
HHO
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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