Chapter 12 Alkenes & Alkynes
Organic and BioChem
• Unsaturated Hydrocarbons • Contain one or more carbon-carbon double or triple bonds
– C3H6?
– C2H2?
• Three Classes of Unsaturated Hydrocarbons • Alkenes:
• Alkynes:
• Arenes:
Section 12.1 Introduction
• Unsaturated Hydrocarbons • Contain one or more carbon-carbon double or triple bonds
– C3H6?
– C2H2?
• Three Classes of Unsaturated Hydrocarbons • Alkenes: Contain Double Bonds
• Alkynes: Contain Triple Bonds
• Arenes: Rings – Benzene compounds (Ch 14)
Section 12.1 Introduction
H
H
H H
H
H
CH CH
Section 12.2 Structure
• Alkenes
Ethylene Propene
Bond Angles?
C C
H
H
H
H
C C
H H
HCH3
Section 12.2 Structure
• Alkenes Ethylene Propene Bond Angles? Id C’s with 109.5 Id C’s with 120
C C
H
H
H
H
C C
H H
HCH3
2-butene cis-trans Isomerism
• cis-2-butene
• trans-2-butene
• Why a Difference?
2-butene cis-trans Isomerism
• cis-2-butene
• trans-2-butene
• Why a Difference? • NO free rotation around Double Bonds!! • Only an issue when double bond is NOT terminal
C C
CH3
H
CH3
H
C C
CH3
H
H
CH3
• Alkynes Ethyne (or Acetylene) Bond Angle?
• cis? trans?
• Alkynes Ethyne (or Acetylene) Bond Angle? 180
• cis? trans? • No worries! LINEAR SHAPE! • There is no “up” or “down”
C CH H
Section 12.3 Nomenclature (Naming)
• Double Bond: • Add - ”ene” to prefix • Base prefix for longest chain that contains the double bond.
Count from end closest to Double Bond • Assign lowest number to double bond CARBON
• Double Bond “cis” “trans”
• Only interior double bonds • Orientation of carbons in parent chain determines “cis” or
“trans” IF YOU DON’T KNOW – DON’T INCLUDE!
• Alkene Name Examples: • CH3(CH2)3CH=CH2
CH3
|
• CH3CH2CHCH=CHCH3
C C
CH2
H
H
CH2CH3
CH3
C C
CH3
H
CH2
CH3
CH3
C C
CH2
CH2
H
HCH
CH3
CH3
CH3
• Alkene Name Examples: • CH3(CH2)3CH=CH2 1-hexene
CH3
|
• CH3CH2CHCH=CHCH3 4-methyl-2-hexene
don’t know “cis” or “trans”
2-ethyl-4-methyl-1-pentene
C C
CH2
H
H
CH2CH3
CH3
C C
CH3
H
CH2
CH3
CH3
trans-3-hexene 3-methyl-cis-2-pentene
C C
CH2
CH2
H
HCH
CH3
CH3
CH3
• Triple Bond: • Add – “yne” to the prefix • Counting rule same as double bonds • No “cis” or “trans” to worry about
• One new EXCEPTION! • Base molecule? CHCH? • Common Name is used in IUPAC • 2 acceptable Names – Both are used.
– Ethyne – Acetylene “common” used more frequently
C CCH H
CH3
CH3
CC CH2CH2CH3 C
CH3
CH3
CH3
3-methyl-1-butyne
6,6-dimethyl-3-heptyne
• Name the following: Which could have cis/trans? CH2=CH(CH2)5CH3
(CH3)2C=C(CH3)2
C CC CH2CH3 CH3
CH3
CH3
C C
H
CH3
CH
CH3
CH3
CH3
C C
CH2
CH2 H
CH2CH2
CH3
CH3
CH3
• Name the following: Which could have cis/trans?
CH2=CH(CH2)5CH3 1-octene
(CH3)2C=C(CH3)2 2,3-dimethyl-2-butene 2,2-dimethyl-3-butyne 3,4-dimethyl-trans-2-pentene 4-ethyl-cis-3-heptene
C CC CH2CH3 CH3
CH3
CH3
C C
H
CH3
CH
CH3
CH3
CH3
C C
CH2
CH2 H
CH2CH2
CH3
CH3
CH3
• Cycloalkenes • Examples 3-methyl-1-cyclopentene 4-ethyl-1-methyl-1-cyclohexene
• Practice
• Cycloalkenes • Examples 3-methyl-1-cyclopentene 4-ethyl-1-methyl-1-cyclohexene
• Practice
3,3-dimethyl 1-cyclohexene
1-isopropyl-4-methyl 1-cyclohexane
4-tertbutyl 1-cyclohexane
• Dienes, trienes, and polyenes • Used when multiple double bonds are found in a chain
•
•
•
CH2=CHCH2CH=CH2
CH3
| CH2=CCH=CH2
• Dienes, trienes, and polyenes • Used when multiple double bonds are found in a chain
• Similar rules to naming substituents are used
• numbers are used to Id location of double bonds
• “di”, “tri”, ect… are used in front of “ene”
CH2=CHCH2CH=CH2
CH3
| CH2=CCH=CH2
2,4-pentadiene
2-methyl-1,3-butadiene also called “isoprene” common name
• Complex diene’s (cis, trans) • 2,4-heptadiene
C C
CH3
H CH
H
CH
CH2 CH3
C C
CH3
H CH
H
CH
CH2 CH3
• Complex diene’s (cis, trans) • 2,4-heptadiene
C C
CH3
H CH
H
CH
CH2 CH3
C C
CH3
H CH
H
CH
CH2 CH3
trans-2-trans-4-heptadiene
trans-2-cis-4-heptadiene
Vitamin A (retinol) • Example of an all-trans alkene chain • An alcohol
CH3 CH3
OH
CH3
CH3 CH3
Vision Molecules • 11-cis-retinal (aldehyde derivative of Vitamin A)
– Reacts with light into All-trans-retinal
• Why is Vitamin A associated with vision? – Our bodies use it as a building block for these molecules
CH3 CH3
CH3
CH3
CH3
O
CH3CH3
CH3
CH3 CH3
O
Naming examples Draw the following
• 3,3-dichloro-1-cyclopentene
• 2,3-dimethyl-2-butene
• trans-2-pentene
• 2,4,4-trimethyl-2-hexene
• 4-bromo-1-cyclohexene
Cl
Cl
CH3
CH3
CH3
CH3CH3 CH3CH3 CH3
H
H
CH3
CH3
CH3CH3
CH3
Br
Sec. 12.4 Properties: Alkenes & Alkynes
• ALL Non-polar compounds
• Only “London Force” intermolecular attractions
• Similar Properties to Alkanes
• Insoluble in WATER.
• Soluble in each other
• ALL less dense than water
Section 12.5 Terpenes
• Terpene
• Isoprene: 2-methyl-1,3-butadiene • Carbon #1 is the head and carbon #4 is the tail • Terpenes are the most widely distributed compounds in the
biological world • Small subunits bonded together by catalyzed enzyme
reactions • Most common are essential oils – used to make perfumes
• Complex Subject: • Linking Isoprene unit together
CH2
CH2
C
CH
CH3
CH2
CH2
C
CH
CH3
Section 12.6 Alkene Reactions
• Addition is the most common reaction
• Breaking and adding across the double bond!
• Addition of hydrogen halides – Add hydrogen halides – HCl, HBr, HI across the double
bond to make alkyl halide
– Halogen substituents are listed in alphabetical order along with substituents (branches) – chloro, bromo, iodo
– Common name is the alkyl group + followed by the name of the halide
• Markovnikov’s Rule • During the addition of HX to an alkene, the hydrogen will
add onto the carbon that has the greatest number of H’s
• Regioselective: The addition of HX is favored in one direction over another
• Markovnikov’s rule does not explain why, it just predicts the favored result
• Example: Propene + HBr
C
C
C
H
H
H
H
H
H
Br H C C CH
H
H
H
Br
H
H
H
• Addition of Water (Hydration): Acid Catalyzed – Water adds across the C=C to form an alcohol (H and
OH) – In the presence of an acid catalyst (H2SO4)
• Draw a structural formula for the product of acid-catalyzed hydration of 1-methylcyclohexene
CH3
42
2
SOHOH
• Hydration Examples • Draw the structural formula for the product of each
alkene hydration CH2
CH3
CH3
42
2
SOHOH
2-methyl-2-butene 42
2
SOHOH
• Addition of Bromine and Chlorine – Carried out with pure reagents or in the presence of CCl4
or CH2Cl2 – Can be used to identify an unknown as an alkene. Br2 is
red but a dibromoalkene is colorless.
•
22
2
ClCHCl
• Addition of Hydrogen (Reduction)
– H2 in the presence of a metal catalyst (Pd, Ni, Pt, Ru) will add hydrogen across the double bond
– Called catalytic reduction or catalytic hydrogenation
CH3CH=CHCH3 PdH2
Ni
H2
Section 12.7 Polymerization of Alkenes
• Most important reaction of Alkenes is the formation of polymers
• Polymers are large molecules made of repeating monomers
• Catalysts called initiators create the chain
• Structure shown by placing the repeating monomer in parentheses
Monomer Formula
Common Name Polymer Name(s) Common uses
CH2=CH2 Ethylene polyethylene, polythene
break resistant containers
CH2=CHCH3 Propylene polypropylene, Herculon
textile and carpet fibers
CH2=CHCl Vinyl chloride poly vinyl chloride (PVC)
construction tubing
CH2=CCl2 1,1-dichloroethylene poly (1,1-dichloroethylene)
Saran Wrap
CH2=CHCN Acrylonitrile polyacrylonitrile, Orion
acrylics & acrylates
CF2=CF2 Tetrafluoroethylene polytetrafluoroethylene, PTFE
Teflon, non-stick coatings
CH2=CHC6H5 Styrene polystyrene, Styrofoam
insulating materials
CH2=CHCOOCH2CH3 Ethyl acrylate poly (ethyl acrylate)
latex paints
CH2=CCOOCH3 | xxxx CH3 xx
Methyl methacrylate poly (methyl methacrylate), Lucite, Plexiglass: Glass substitutes
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