Unsaturated Hydrocarbons Physical properties – Similar to saturated hydrocarbons Chemical 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 hydrocarbons Chemical 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 Bonds  Carbon-carbon multiple bonds (ex.: C 2 H 4 ) 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 1.When a single bond is present between two atoms, that bond is always a  -bond. 2.When a double bond is present between two atoms, that bond consists of one  -bond and one  -bond. 3.When a triple bond is present between two atoms, that bond always consists of one  -bond and two  -bonds.  Importance of  -bonds 1.A carbon-carbon  -bond is weaker, consequently more reactive 2.The presence of the  -bond causes the bond to be structurally rigid. There is no free rotation. 3.The  -bond must be broken for rotation to occur.  Carbon-carbon multiple bonds (ex.: C 2 H 4 ) 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 1.When a single bond is present between two atoms, that bond is always a  -bond. 2.When a double bond is present between two atoms, that bond consists of one  -bond and one  -bond. 3.When a triple bond is present between two atoms, that bond always consists of one  -bond and two  -bonds.  Importance of  -bonds 1.A carbon-carbon  -bond is weaker, consequently more reactive 2.The presence of the  -bond causes the bond to be structurally rigid. There is no free rotation. 3.The  -bond must be broken for rotation to occur.

Classes of Unsaturated Hydrocarbons  1.Alkenes – An acyclic hydrocarbon with one or more carbon-carbon double bonds (with one double bond : C n H 2n )  2.Alkynes – An acyclic hydrocarbon with one or more carbon-carbon triple bonds (with one triple bond : C n H 2n-2 )  3.Aromatic – A cyclic hydrocarbon six*-carbon (usually) ring containing three carbon-carbon double bonds. * known as a benzene ring (C 6 H 6 ).  1.Alkenes – An acyclic hydrocarbon with one or more carbon-carbon double bonds (with one double bond : C n H 2n )  2.Alkynes – An acyclic hydrocarbon with one or more carbon-carbon triple bonds (with one triple bond : C n H 2n-2 )  3.Aromatic – A cyclic hydrocarbon six*-carbon (usually) ring containing three carbon-carbon double bonds. * known as a benzene ring (C 6 H 6 ).

Alkenes  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 CC  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 CC  C---C

In ethene, the atoms are in a flat (planar) rather than a tetrahedral arrangement. Ethene is the compound that causes tomatoes to ripen.

 Bonding in Ethene

H HH C H C Top View C 2 H 4

Nomenclature 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.:  3-Pentene  1,3-Pentadiene  2,4,6-Octatriene  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.:  3-Pentene  1,3-Pentadiene  2,4,6-Octatriene  6-Methyl-2,4-octadiene

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.  Ex.:  Cyclopentene  3-Ethylcyclopentene  1,4-Cyclooctadiene  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.  Ex.:  Cyclopentene  3-Ethylcyclopentene  1,4-Cyclooctadiene  6-propyl-1,4-Cyclooctadiene

Alkenyl Groups  There are THREE important such groups:  Methylene (CH 2 =)  methylidene  Vinyl (CH 2 =CH-)  ethenyl  Ex. Vinyl chloride (CH 2 =CHCl)  Allyl (CH 2 =CH-CH 2 -)  2-propenyl  There are THREE important such groups:  Methylene (CH 2 =)  methylidene  Vinyl (CH 2 =CH-)  ethenyl  Ex. Vinyl chloride (CH 2 =CHCl)  Allyl (CH 2 =CH-CH 2 -)  2-propenyl

Structural Isomerism 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 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  Trans-3-Methyl-3-hexene  Cis-2-Pentene  Trans-2-Pentene CH 3 CH 2 — CH 3 \ / C=C / \ H H  Cis-1-chloro-1-pentene  Trans-3-Methyl-3-hexene  Cis-2-Pentene  Trans-2-Pentene CH 3 CH 2 — CH 3 \ / C=C / \ H H  Cis-1-chloro-1-pentene

Occurrence  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 O 2 )  Ethane ---> Ethene + H 2  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 O 2 )  Ethane ---> Ethene + H 2

Physical Properties  Solubility  Insoluble in water  Soluble in nonpolar solvents  Less dense than water  Lower melting point than alkanes  Physical states similar to alkanes  C 1 to C 5 = gas  C 6 to C 17 = liquid  > C 17 = solid  Solubility  Insoluble in water  Soluble in nonpolar solvents  Less dense than water  Lower melting point than alkanes  Physical states similar to alkanes  C 1 to C 5 = gas  C 6 to C 17 = liquid  > C 17 = solid

Chemical Reactions  Addition  Symmetrical: -C=C- + X 2 --> 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- + X 2 --> 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 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

Alkynes  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 Acetylene

C2H2C2H2 C2H2C2H2 C C H H

Alkenynes  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.

Aromatics  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  One substituent derivatives:  Use IUPAC system  Ex.: methylbenzene; bromobenzene  BUT, several of these are considered new Parent molecules:  Toluene  Styrene  Phenol  One substituent derivatives:  Use IUPAC system  Ex.: methylbenzene; bromobenzene  BUT, several of these are considered new Parent molecules:  Toluene  Styrene  Phenol

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

Occurances  Coal Tar  Petroleum  Synthetic  Ex.: C 7 H > Toluene + 4H 2  Coal Tar  Petroleum  Synthetic  Ex.: C 7 H > Toluene + 4H 2

Physical Properties & Chemical Reactions  Good solvent for non-polar molecules!  Alkylation reactions:  Benzene + R-Cl --->  Halogenation:  Benzene + Cl 2 --->  Polymerization  Styrene --> Polystyrene  Largest Synthetic Molecule Largest Synthetic Molecule  Good solvent for non-polar molecules!  Alkylation reactions:  Benzene + R-Cl --->  Halogenation:  Benzene + Cl 2 --->  Polymerization  Styrene --> Polystyrene  Largest Synthetic Molecule Largest Synthetic Molecule

Fused-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?  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