Unsaturated HydrocarbonsUnsaturated Hydrocarbons

Physical properties – Similar to saturated hydrocarbonsChemical properties -

1.More reactive than saturated hydrocarbons

2.The carbon-carbon double or triple bonds are the reactive sites

(In most cases we will be working with double bonds)

So, common reactive sites are: Multiple bond sites Functional group sites

Physical properties – Similar to saturated hydrocarbonsChemical properties -

1.More reactive than saturated hydrocarbons

2.The carbon-carbon double or triple bonds are the reactive sites

(In most cases we will be working with double bonds)

So, common reactive sites are: Multiple bond sites Functional group sites

Multiple BondsMultiple Bonds Carbon-carbon multiple bonds (ex.: C2H4)

1. There are two types of bonds in carbon-carbon multiple bonds a. Sigma bonds () – A covalent bond in which atomic orbital overlap

occurs along the axis joining the two bonded carbons b. Pi bonds () – A covalent bond in which atomic orbital overlap occurs

above and below, but not on, the internuclear axis.

Occurrence of and bonds When a single bond is present between two atoms, that bond is always a -

bond. When a double bond is present between two atoms, that bond consists of one

-bond and one -bond. When a triple bond is present between two atoms, that bond always consists of

one -bond and two -bonds.

Importance of -bonds A carbon-carbon -bond is weaker, consequently more reactive The presence of the -bond causes the bond to be structurally rigid. There is

no free rotation. The -bond must be broken for rotation to occur.

Carbon-carbon multiple bonds (ex.: C2H4)1. There are two types of bonds in carbon-carbon multiple bonds

a. Sigma bonds () – A covalent bond in which atomic orbital overlap occurs along the axis joining the two bonded carbons

b. Pi bonds () – A covalent bond in which atomic orbital overlap occurs above and below, but not on, the internuclear axis.

Occurrence of and bonds When a single bond is present between two atoms, that bond is always a -

bond. When a double bond is present between two atoms, that bond consists of one

-bond and one -bond. When a triple bond is present between two atoms, that bond always consists of

one -bond and two -bonds.

Importance of -bonds A carbon-carbon -bond is weaker, consequently more reactive The presence of the -bond causes the bond to be structurally rigid. There is

no free rotation. The -bond must be broken for rotation to occur.

Classes of Unsaturated Hydrocarbons

Classes of Unsaturated Hydrocarbons

1. Alkenes – An acyclic hydrocarbon with one or more carbon-carbon double bonds (with one double bond : CnH2n)

2. Alkynes – An acyclic hydrocarbon with one or more carbon-carbon triple bonds (with one triple bond : CnH2n-2)

3. Aromatic – A cyclic hydrocarbon six*-carbon (usually) ring containing three carbon-carbon double bonds.

* known as a benzene ring (C6H6).

1. Alkenes – An acyclic hydrocarbon with one or more carbon-carbon double bonds (with one double bond : CnH2n)

2. Alkynes – An acyclic hydrocarbon with one or more carbon-carbon triple bonds (with one triple bond : CnH2n-2)

3. Aromatic – A cyclic hydrocarbon six*-carbon (usually) ring containing three carbon-carbon double bonds.

* known as a benzene ring (C6H6).

AlkenesAlkenes An alkene can be formed by removing a hydrogen atom

from two adjacent carbons in a carbon chain. Ex: Hexane -C—C—C—C—C—C- becomes Hexene -C—C—C=C—C—C- (3-Hexene)

Ex: Ethane -C-C- becomes Ethene -C=C-

(also known as ethylene)

Ex.:Cycloalkenes C---C cyclohexene C C

C---C

An alkene can be formed by removing a hydrogen atom from two adjacent carbons in a carbon chain. Ex: Hexane -C—C—C—C—C—C- becomes Hexene -C—C—C=C—C—C- (3-Hexene)

Ex: Ethane -C-C- becomes Ethene -C=C-

(also known as ethylene)

Ex.:Cycloalkenes C---C cyclohexene C C

C---C

In ethene, the atoms are in a flat (planar) rather than a tetrahedral arrangement.

In ethene, the atoms are in a flat (planar) rather than a tetrahedral arrangement.

Ethene is the compound that causes tomatoes to ripen.

QuickTime™ and aGraphics decompressor

are needed to see this picture.

Bonding in EtheneBonding in Ethene Bonding in Ethylene Bonding in Ethylene

2 2 spsp22

pp

each carbon has an unhybridized 2each carbon has an unhybridized 2pp orbital orbital

axis of orbital is perpendicular to the plane of the axis of orbital is perpendicular to the plane of the σσ bonds bonds

Bonding in EtheneBonding in Ethene Bonding in Ethylene Bonding in Ethylene

2 2 spsp22

pp

side-by-side overlap of half-filledside-by-side overlap of half-filled

pp orbitals gives a orbitals gives a π π bondbond

double bond in ethylene has a double bond in ethylene has a

σσ component and a component and a ππ component component

H

HH

CH

C

Top View C2H4Top View C2H4

Nomenclature of AlkenesNomenclature of Alkenes

1. Select the parent carbon chain with the longest chain of carbon atoms that contains the double bond.

2. Replace the alkane suffix –ane with –ene to indicate the presence of a double bond.

3. Number the carbon chain starting with the end of the chain that has the closest double bond.

4. Indicate location of the double bond using the lowest carbon number of the carbons associated with the double bond.

5. If more than one double bond is present use the suffixes diene, triene, tetraene, ect. The associated carbon numbers are used to indicate the position of the double bonds.

Ex.:

1. 3-Pentene2. 1,3-Pentadiene3. 2,4,6-Octatriene4. 6-Methyl-2,4-octadiene

1. Select the parent carbon chain with the longest chain of carbon atoms that contains the double bond.

2. Replace the alkane suffix –ane with –ene to indicate the presence of a double bond.

3. Number the carbon chain starting with the end of the chain that has the closest double bond.

4. Indicate location of the double bond using the lowest carbon number of the carbons associated with the double bond.

5. If more than one double bond is present use the suffixes diene, triene, tetraene, ect. The associated carbon numbers are used to indicate the position of the double bonds.

Ex.:

1. 3-Pentene2. 1,3-Pentadiene3. 2,4,6-Octatriene4. 6-Methyl-2,4-octadiene

Nomenclature of Cycloalkenes

Nomenclature of Cycloalkenes

1. If there is only one double bond, its position does not need to be indicated. It is assumed to be located between carbons one and two.

2. If there is more than one double bond in the ring, number the bond locations in a manner that will give the lowest numbers.

3. In substituted cycloalkenes assign the numbers in a manner that will produce the lowest combination of numbers.

1. Ex.:2. Cyclopentene3. 3-Ethylcyclopentene4. 1,4-Cyclooctadiene5. 6-propyl-1,4-Cyclooctadiene

1. If there is only one double bond, its position does not need to be indicated. It is assumed to be located between carbons one and two.

2. If there is more than one double bond in the ring, number the bond locations in a manner that will give the lowest numbers.

3. In substituted cycloalkenes assign the numbers in a manner that will produce the lowest combination of numbers.

1. Ex.:2. Cyclopentene3. 3-Ethylcyclopentene4. 1,4-Cyclooctadiene5. 6-propyl-1,4-Cyclooctadiene

Alkenyl GroupsAlkenyl Groups There are THREE important such

groups: Methylene (CH2=)

methylidene

Vinyl (CH2=CH-) ethenyl Ex. Vinyl chloride (CH2=CHCl)

Allyl (CH2=CH-CH2-) 2-propenyl

There are THREE important such groups: Methylene (CH2=)

methylidene

Vinyl (CH2=CH-) ethenyl Ex. Vinyl chloride (CH2=CHCl)

Allyl (CH2=CH-CH2-) 2-propenyl

Structural IsomerismStructural Isomerism1. Structural isomer can occur as they do with alkanes

• Positional: 1-butene vs. 2-butene• Skeletal: 1-butene vs. 2-methylpropene

2. The carbon-carbon double bond allows the formation of two additional types of isomers, Cis-and Trans- isomers (these are also known as stereoisomers)

a) The double bond restricts rotation around the C atoms.b) The carbons must have two different types of groups

attached to them* A hydrogen functional group* A carbon containing group or a halogen

c) To determine whether cis or trans occurs draw the molecule and examine the shape.

Ex.: 2-butene Ex.: Retinal/Opsin

1. Structural isomer can occur as they do with alkanes• Positional: 1-butene vs. 2-butene• Skeletal: 1-butene vs. 2-methylpropene

2. The carbon-carbon double bond allows the formation of two additional types of isomers, Cis-and Trans- isomers (these are also known as stereoisomers)

a) The double bond restricts rotation around the C atoms.b) The carbons must have two different types of groups

attached to them* A hydrogen functional group* A carbon containing group or a halogen

c) To determine whether cis or trans occurs draw the molecule and examine the shape.

Ex.: 2-butene Ex.: Retinal/Opsin

Examples of Structural Isomers

Examples of Structural Isomers

Trans-3-Methyl-3-hexene

Cis-2-Pentene

Trans-2-Pentene

CH3 CH2—CH3

\ /C=C

/ \ H H

Cis-1-chloro-1-pentene

Trans-3-Methyl-3-hexene

Cis-2-Pentene

Trans-2-Pentene

CH3 CH2—CH3

\ /C=C

/ \ H H

Cis-1-chloro-1-pentene

OccurrenceOccurrence

Natural Pheromones Terpenes (plant odors & fragrances)

Contain 2 or more isoprene units (2-methyl-1,3-butadiene)

Synthetic Dehydrogenation of Alkanes (at

high temperature and in absence of O2)Ethane ---> Ethene + H2

Natural Pheromones Terpenes (plant odors & fragrances)

Contain 2 or more isoprene units (2-methyl-1,3-butadiene)

Synthetic Dehydrogenation of Alkanes (at

high temperature and in absence of O2)Ethane ---> Ethene + H2

Physical PropertiesPhysical Properties Solubility

Insoluble in water Soluble in nonpolar solvents

Less dense than water Lower melting point than alkanes Physical states similar to alkanes

C1 to C5 = gas C6 to C17 = liquid > C17 = solid

Solubility Insoluble in water Soluble in nonpolar solvents

Less dense than water Lower melting point than alkanes Physical states similar to alkanes

C1 to C5 = gas C6 to C17 = liquid > C17 = solid

Chemical ReactionsChemical Reactions Addition

Symmetrical: -C=C- + X2 --> X-C-C-X Hydrogenation - results in formation of alkane Halogenation*

Asymmetrical: -C=C- + AB --> A-C-C-B Hydrohalogenation Hydration - results in formation of alcohol Markovnikov’s* rule: (“rich get richer”)

Hydrogen goes to C with most hydrogens.

Addition Symmetrical: -C=C- + X2 --> X-C-C-X

Hydrogenation - results in formation of alkane Halogenation*

Asymmetrical: -C=C- + AB --> A-C-C-B Hydrohalogenation Hydration - results in formation of alcohol Markovnikov’s* rule: (“rich get richer”)

Hydrogen goes to C with most hydrogens.

A bromine in water solution is reddish brown. When a small amount of such a solution is added to an unsaturated hydrocarbon, the added

solution is decolorized.

Chemical ReactionsChemical Reactions Polymerization: multiple simple molecules

(monomers) add together to form a single, larger molecule (polymer) These are usually catalyzed reactions!

Addition polymers C=C + C=C + C=C --> C-C-C-C-C-C (polyethylene) (C-C)n

Substituted-ethene addition polymers nC=C-X --> (C-C-X)n (ex.: PVC)

Butadiene-based addition polymers Ex.: natural rubber (2-methyl-1,3-butadiene; isoprene) Much more flexible than other polymers

Addition Copolymers (two different monomers) Ex.: Saran wrap (1953) - polyvinylidene chloride

(2004) - polyethylene

Polymerization: multiple simple molecules (monomers) add together to form a single, larger molecule (polymer) These are usually catalyzed reactions!

Addition polymers C=C + C=C + C=C --> C-C-C-C-C-C (polyethylene) (C-C)n

Substituted-ethene addition polymers nC=C-X --> (C-C-X)n (ex.: PVC)

Butadiene-based addition polymers Ex.: natural rubber (2-methyl-1,3-butadiene; isoprene) Much more flexible than other polymers

Addition Copolymers (two different monomers) Ex.: Saran wrap (1953) - polyvinylidene chloride

(2004) - polyethylene

AlkynesAlkynes

Formation is similar to that of alkenes (more hydrogens are removed; higher temp.) Ethyne = Acetylene

Naming: same rules as for alkenes Isomerism: cis-trans NOT possible

Linear geometry around the triple bond Properties & Reactions are similar to

those of alkenes

Formation is similar to that of alkenes (more hydrogens are removed; higher temp.) Ethyne = Acetylene

Naming: same rules as for alkenes Isomerism: cis-trans NOT possible

Linear geometry around the triple bond Properties & Reactions are similar to

those of alkenes

Bonding in AcetyleneBonding in Acetylene Bonding in Acetylene Bonding in Acetylene

one one ππ bond involves one of the p orbitals on each carbon bond involves one of the p orbitals on each carbon

there is a second there is a second ππ bond perpendicular to this one bond perpendicular to this one

2 2 spsp

2 2 pp

Bonding in AcetyleneBonding in Acetylene Bonding in Acetylene Bonding in Acetylene

2 2 spsp

2 2 pp

Bonding in AcetyleneBonding in Acetylene Bonding in Acetylene Bonding in Acetylene

2 2 spsp

2 2 pp

C2H2C2H2

C C HH

AlkenynesAlkenynes Hydrocarbons with both double &

triple bonds. Naming: Double bond has priority #ing Carbons: from end closest to a

multiple bond.

Hydrocarbons with both double & triple bonds. Naming: Double bond has priority #ing Carbons: from end closest to a

multiple bond.

AromaticsAromatics Unsaturated cyclic hydrocarbons

which do not readily undergo addition reactions.

Benzene: the foundation molecule Contains both localized and delocalized bonds

Unsaturated cyclic hydrocarbons which do not readily undergo addition reactions.

Benzene: the foundation molecule Contains both localized and delocalized bonds

Naming Benzene Derivatives

Naming Benzene Derivatives

One substituent derivatives: Use IUPAC system

Ex.: methylbenzene; bromobenzene

BUT, several of these are considered new Parent molecules:TolueneStyrenePhenol

One substituent derivatives: Use IUPAC system

Ex.: methylbenzene; bromobenzene

BUT, several of these are considered new Parent molecules:TolueneStyrenePhenol

Naming Benzene Derivatives

Naming Benzene Derivatives

Two substituent derivatives: Use the following prefixes to

indicate substituent position:Ortho (1,2)Meta (1,3)Para (1,4)

Xylene (dimethylbenzene) p-dichlorobenzene

Two substituent derivatives: Use the following prefixes to

indicate substituent position:Ortho (1,2)Meta (1,3)Para (1,4)

Xylene (dimethylbenzene) p-dichlorobenzene

OccurancesOccurances

Coal Tar Petroleum

Synthetic Ex.: C7H16 ---> Toluene + 4H2

Coal Tar Petroleum

Synthetic Ex.: C7H16 ---> Toluene + 4H2

Physical Properties & Chemical Reactions

Physical Properties & Chemical Reactions

Good solvent for non-polar molecules!

Alkylation reactions: Benzene + R-Cl --->

Halogenation: Benzene + Cl2 --->

Polymerization Styrene --> Polystyrene

Largest Synthetic Molecule

Good solvent for non-polar molecules!

Alkylation reactions: Benzene + R-Cl --->

Halogenation: Benzene + Cl2 --->

Polymerization Styrene --> Polystyrene

Largest Synthetic Molecule

Fused-Ring AromaticsFused-Ring Aromatics Naphthalene

Carcinogenic Fused-ring aromatics: 4+ fused rings Same “angle” in ring series Form when hydrocarbons are

heated to high temperatures

Naphthalene

Carcinogenic Fused-ring aromatics: 4+ fused rings Same “angle” in ring series Form when hydrocarbons are

heated to high temperatures

What do you need to know?

What do you need to know?

Structural characteristics (know the functional group)

Alkene Alkyne Aromatic

Nomenclature (the rules for naming the molecules) Physical and Chemical properties (basic/simple)

Occurrence and uses (common)

Preparation (what basic reactions produce the molecules)

Characteristic reactions of the molecules

Structural characteristics (know the functional group)

Alkene Alkyne Aromatic

Nomenclature (the rules for naming the molecules) Physical and Chemical properties (basic/simple)

Occurrence and uses (common)

Preparation (what basic reactions produce the molecules)

Characteristic reactions of the molecules