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