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Chem 1152: Ch. 12
Unsaturated Hydrocarbons
Types of HydrocarbonsTypes of Hydrocarbons• Saturated: All C—C bonds are single bonds• Unsaturated: Hydrocarbons with one or more multiple bonds• The term unsaturated is used because C could bind more H (become
saturated) if no multiple bonds existed.
1. Alkenes (ethylene)
C C
H
H H
H
2. Alkynes (acetylene)
C CH H
3. Aromatics (benzene)
H
H
H
H
H
H
Rules for Naming AlkenesRules for Naming Alkenes
1. Name the longest chain that contains the double bond or double bonds. The name of the chain will end in –ene.
2. Number this longest chain so the C=C bond or bonds has/have the lowest number.
3. The first C of the C=C bond (for C=C bond to have lowest number) identifies the positional location of the double bond.
4. Name the attached functional groups.5. Combine the names of the attached groups and longest
chain, the same as you would with alkanes.6. For multiple double bonds, indicate the locations of all
multiple bonds, use numeric prefixes indicating number of double bonds (-diene, -triene).
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Naming AlkenesNaming Alkenes• Step 1: Name the longest chain that contains the C=C bond.
Use the IUPAC root and the –ene ending.• Step 2: Number the longest chain so the C=C bond gets the
lowest number possible.• Step 3: Locate the C=C bond with the lower-numbered
carbon. Examples: 1 2 3 4 CH3-CH=CH-CH3
2-butene
6 5 4 3 2 1 CH3-CH2-CH2-CH=CH-CH3
2-hexene
Naming Alkenes (continued)Naming Alkenes (continued)
• Step 4: Locate and name attached groups.• Step 5: Combine all the names.
Naming AlkenesNaming Alkenes
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
CH3 CH3CH CH CH2
CH3 CH2
C CH2
CH2CH2CH2CH3
C
CH2CH2CH2CH3
CH2 CH2 CH3
CH3
C
CH3 H
2-pentene
2-ethyl-1-hexene
5-ethyl-3-methyl-2-octene
C
CH2CH2
CH2 C
C
CH3
CH2CH2
CH3
Br
CH
4-methylcyclohexene
3-bromo-2-methyl-1-propene
Alkene ExamplesAlkene Examples
2-methylpent-2-ene (3Z)-3-methylhex-3-ene
Br
(3E)-3-bromo-4-methylhex-3-ene
(3Z)-3,4,5-trimethylhept-3-ene
ICl
(2Z,4E)-1-chloro-5-iodo-2,4-dimethylhexa-2,4-diene
(4Z)-3,4,7-trimethylocta-1,4,6-triene
(2E)-but-2-ene
4-methylcyclohexene
Br
(5S)-5-bromocyclohexa-1,3-diene
H
Cl
5-chlorocyclopenta-1,3-diene
The Geometry of AlkenesThe Geometry of Alkenes
• In C=C bonds, sp2 hybrid orbitals are formed by the carbon atoms, with one electron left in a 2p orbital. A representation of sp2 hybridization of carbon.
• During hybridization, two of the 2p orbitals mix with the single 2s orbital to produce three sp2 hybrid orbitals. One 2p orbital is not hybridized and remains unchanged.
2p2s1s
Energy
2p3 sp2
1s
The Geometry of Alkenes (continued)The Geometry of Alkenes (continued)
1. One bond (sigma, σ) is formed by overlap of two sp2 hybrids.
2. The second bond (pi, π) is formed by connecting the unhybridized p orbitals.
2p2s1s
Energy
2p3 sp2
1s
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
The Geometry of Alkenes (continued)The Geometry of Alkenes (continued)
– The planar geometry of the sp2 hybrid orbitals and the ability of the 2p electron to form a “pi bond” bridge locks the C=C bond firmly in place.
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
The Geometry of Alkenes (continued)The Geometry of Alkenes (continued)
• Because there is no free rotation about the C=C bond, geometric isomerism is possible.
• cis- isomers have two similar or identical groups on the same side of the double bond.
• trans- isomers have two similar or identical groups on opposite sides of the double bond.
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
The Geometry of Alkenes (continued)The Geometry of Alkenes (continued)• Geometric isomers have different physical properties.
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Geometric (cis-trans) Isomerism in AlkenesGeometric (cis-trans) Isomerism in Alkenes• By definition, must have 2 different groups attached to each double
bonded carbon.
HH
C C
CH3 CH3
H
C C
CH3 H
CH3
HH
C C
CH3 CH3
CH3
C C
H H
CH3
HH
C C
CH3 H
H
C C
H H
CH3
Geometric Isomers?
Yes
No
No
Which of the following can exhibit cis-trans isomerism? Cl-CH=CH-Cl CH2=CHCH3 Cl-CH=CHCH3
Properties of Alkanes and AlkenesProperties of Alkanes and Alkenes
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Alkanes Alkenes Non-polar Water insoluble Alkanes have lower MP and
lower BP than other organic compounds
Odorless Less dense than water As alkane gets bigger:
o BP increases o MP increases o Density increases
Non-polar Water insoluble Soluble in non-polar solvents Less dense than water As alkene gets bigger:
o BP increases o MP increases o Density increases
More reactive than alkanes due to C=C bond
Types of Alkene ReactionsTypes of Alkene Reactions
• The double-bond in alkenes make them chemically reactive
• Four major types of alkene reactions– Addition– Elimination– Substitution– Rearrangement
C=C
Addition ReactionsAddition Reactions
• Two reactants add together to form a single new product that includes all original atoms.
• Double bond becomes a single bond.
A + B C
C C C CX--Y+
X Y
Addition ReactionsAddition Reactions
• Halogenation: Addition of a Halide (fluorine, chlorine, bromine, iodine).
CH2CH3CH2CH Br-Br
Br
+ CH2CH3CH2CH
Br1-butene 1,2-dibromobutane
CHCH3CH3CH
H
+
H2-butene butane
H2 CHCH3CH3CH
• Hydrogenation: Metal (Pt, Pd or Ni) catalyzed addition of hydrogen atoms to C=C bond.
Pt
Addition ReactionsAddition Reactions• Acid Rxn: (HCl, HBr, etc.)• The major product of this rxn is 2-bromopropane, due to:• Markovnikov’s rule: When H-X reacts with alkene, H goes to
C that already has the most H.
CHCH3CH2
Br+
HHBr
CHCH3CH2
H Br
CHCH3CH2
1-bromopropane
2-bromopropane
ClH
H
CH3
Br
CH3
HH
+
Addition ReactionsAddition Reactions• Hydration: Water may react with alkene in presence of acid
catalyst
CH2CH3CH + H-OHOH H
H2SO4 CH2CH3CH
• Rxn also follows Markovnikov’s rule• This method can be used for large scale production of
alcohols
Addition ReactionsAddition Reactions• Polymerization: Addition rxn where identical molecules join
together to form long chains.
• This rxn can produce very long, inert alkane chains, useful in manufacture of food storage containers.
(CH2=CH2)Heat, P
Catalyst(CH2=CH2) (CH2=CH2)
polyethylene
Addition ReactionsAddition Reactions• Copolymerization: Addition rxn with 2 different monomers.
Note: --CH=CH2 is known as a vinyl group
CHCH2 +catalyst
ClCCH2
Cl
ClCH2
Cl
CH CCH2
Cl
Cl
vinyl chloride vinylidine chloride Saran wrap
Elimination ReactionsElimination Reactions
• Single reactant becomes multiple products.• Single bond becomes a double bond.
A B + C
C C C C
X Y
+ X--Y
Substitution ReactionsSubstitution Reactions
• 2 reactants exchange parts, create 2 new products.
C + R--Y
X
C + R--X
Y
Rearrangement ReactionsRearrangement Reactions
• Single reactant reorganized into isomer.
C CH H
HCH3CH2
C CH
HCH3
CH3
Acid Catalyst (H+)
Geometry of AlkynesGeometry of Alkynes• Copolymerization: Addition rxn with 2 different monomers.
2p2s1s
Energy
2p2 sp1s
• Insoluble in water
• Less dense than water
• Low MP, BP
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
AromaticsAromatics• 6 C ring structures with alternating double bonds (benzene).• Everything that is not aromatic, is aliphatic (alkanes, alkenes,
alkynes).• Early problem chemists found was that benzene was not
reactive (recall that alkenes are reactive due to double bond).• Kekule proposed that double bonds alternated between 2
equivalent structures• electrons move around a conjugated pi bond system of rings• Stabilizes structure and makes it less reactive.
Naming Benzene DerivativesNaming Benzene Derivatives1. For single replacement (H some FG), cmpd named as a
benzene derivative.CH3
N+ O
-O
CH3 OH
CH3CH3OHO
propylbenzene nitrobenzene methylbenzene hydroxybenzene
isopropylbenzene carboxybenzene
Naming Benzene Derivatives (continued)Naming Benzene Derivatives (continued)
Some common names are IUPAC-accepted and used preferentially.
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Naming Benzene DerivativesNaming Benzene Derivatives• Some benzene derivatives better known by common names
accepted by IUPAC.NH2
aniline commonaminobenzene IUPAC
• The benzene ring can also be an attached substituent group.
CH3 CH3
4-phenylheptane 1,1-diphenylcyclobutane
Naming Benzene DerivativesNaming Benzene Derivatives• With only 2 groups on benzene ring, can use o, m, p (ortho,
meta, para) nomenclature.
CH3
CH3
CH3
CH3
CH3
CH3
o- m- p-
p-methylanilinep-aminotoluene
m-dichlorobenzeneo-nitrotoluene
CH3 N+
O-
OCl
Cl
NH2
CH3
Naming Benzene DerivativesNaming Benzene Derivatives• When 2 or more groups are attached to benzene ring, positions can be
indicated by numbering ring C atoms to obtain lowest possible numbers.
Br
Br
Br Br
Cl Cl
Cl
CH3
OH
OOH
1,2,3,5-tetrabromobenzene 1,2,4-trichlorobenzene
3-hydroxy-4-methylbenzoic acid
This could be named as either a disubstituted:toluenephenolbenzoic acid
Naming AlkynesNaming Alkynes• Name of the compound ends in -yne.• The longest chain chosen for the root name must include both carbon atoms of
the triple bond.• The root chain must be numbered from the end nearest a triple bond carbon atom.
– If the triple bond is in the center of the chain, the nearest substituent rule is used to determine the end where numbering starts.
• The smaller of the two numbers designating the carbon atoms of the triple bond is used as the triple bond locator.
• If several multiple bonds are present, each must be assigned a locator number. Double bonds precede triple bonds in the IUPAC name, but the chain is numbered from the end nearest a multiple bond, regardless of its nature. The name will then have multiplier prefix (e.g., diyne, triyne, etc.)
• Because the triple bond is linear, it can only be accommodated in rings larger than ten carbons. In simple cycloalkynes the triple bond carbons are assigned ring locations #1 and #2. Which of the two is #1 may be determined by the nearest substituent rule.
• Substituent groups containing triple bonds are: HC≡C– Ethynyl group
33
CH3 CH3
Examples of AlkynesExamples of Alkynes
CH3
CH3
Br
CH3 CH3
CH3
CH3
BrCH
CH3
but-2-yne pent-2-yne hex-3-yne
2-bromohex-3-yne 5-bromohexa-1,3-diyne
Examples of AlkynesExamples of Alkynes
CH3
CH3
CH3
4-methyl-2-pentyne
1-cyclopentyl-1-butyneCH3
1,6-dichloro-2,2-dimethyl-3-hexyneCH3 CH3
ClCl
1-phenyl-1,4-pentadiyneCH
cis-1,2-diethynylcyclobutaneCHCH
CH3
CH3
2-hexyne
Examples of AlkynesExamples of Alkynes
CH3
CH3
CH3
4-methyl-2-pentyne
1-cyclopentyl-1-butyneCH3
1,6-dichloro-2,2-dimethyl-3-hexyneCH3 CH3
ClCl
1-phenyl-1,4-pentadiyneCH
cis-1,2-diethynylcyclobutaneCHCH
CH3
CH3
2-hexyne