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Unsaturated Hydrocarbons
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• Introduction to Unsaturated HC– One or more C-to-C multiple bond present• Double bond is rigid – doesn’t rotate
– Similar physical properties to saturated HC– Very different chemical properties than sat’d HC• Unsat’d HC are MUCH more reactive than saturated HC• Reactions take place at the multiple bond
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• When a specific portion of the molecule determines its reactivity that part of the molecule is called a functional group– C-to-C multiple bonds are an example of a
functional group
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Classes of Unsaturated HC
• Alkenes – C-to-C double bond(s) present • may be acyclic or cyclic
• Alkynes – C-to-C triple bond(s) present• Aromatic – unsaturated cyclic HC that does
not undergo addition reactions readily– Often a benzene ring present
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Alkenes and Cycloalkenes• Functional group: C=C– ALKENES: acyclic alkene
• General formula if only 1 double bond is present: CnH2n
• ??same as…….
Example: • Cycloalkenes: cyclic alkene
• general formula if only one double bond is present: CnH2n - 2
Example:
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Naming Alkenes• Name longest continuous chain that contains
the double bond, suffix = “ene”– If C=C is same distance from both ends, start
numbering from end closest to any substituent• Locate C=C by giving # of the lowered
numbered C in the double bond• Use suffixes of “diene”, “triene”, tetrene” if
more than one C=C– 1,3-hexadiene
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Naming Cycloalkenes
• Name ring as you would a cycloalkane, but using suffix of “ene”– Cyclopentene….. no # needed to locate C=C
• If there are substituents on the ring– Cs of the double bond are C 1 and 2 – no #needed
to locate C=C in name– Number so substituent(s) have lowest possible #– List in alphabetical order if more than 1
substituent
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More naming
• Practice: Page 73, 16 and 20• Common Names to Know– Ethylene
– Propylene
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Line Angle Formulas
• Pretty straightforward• Try a few on page 73: 26 & 28
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Isomerism in Alkenes
1. Constitutional– Positional isomers…location of double different – Skeletal isomers …longest chain differs
2. Stereoisomers– Cis-trans isomers possible when:• Each C in double bond has 2 different groups attached
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Naturally Occurring Alkenes
• Pages 50-52• Good paper potential– Pheremones– Retenoids– Terpenes and isoprenes
• No coverage in lecture
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Physical Properties
1. Nonpolar– Solubility
2. Density3. MP and BP - trends4. State at room temperature– For unbranched alkenes
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Chemical Properties Alkenes
1. Combustion reaction2. Addition reactions– Symmetrical: H2 and X2
– Unsymmetrical: HX and H-OH• Markovnikov’s Rule applies
3. Polymerization reaction – Not covered, good paper topic
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Alkynes
• Limited coverage in class• See pages 62-64
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Bond Angles
• Alkanes
• Alkenes
• Alkynes
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Aromatic Hydrocarbons
• Cyclic unsaturated HC that does not undergo addition reactions– delocalized electrons electrons present
• Our focus will be on benzene based aromatic HC– Structure– Naming conventions– Properties: physical and chemical (selected)
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Benzene and Benzene Derivatives
• Benzene• Toluene– NOT methylbenzene
• Single substituent – put name of substituent in front of benzene– Chlorobenzene– tertbutylbenzene
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2 Substituents - 2 Naming Options
1. Number system– Locate substituents with #s– Goal is lowest possible set of #s– When substituents differ, that with alphabetical
priority is assigned #1…see top of page 68 – When a methyl group is one of the
substituents….
2. Ortho, meta, para system– 2 methyl groups a xylene
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Benzene as a Substituent!
• Benzene “hanging off” a chain = a phenyl group– See example 2.6 c on page 68
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Properties of Aromatic HC (benzene)
1. Physical properties– You know these….polarity, solubility, density,
state of matter of benzene
2. Chemical properties – many, text covers 2– Alkylation: + R-Cl • AlCl3 catalyst required
– Halogenation: + X2
• FeX3 catalyst required