Chapter 5 - Structure and Preparation of Alkenes...

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Structure and Preparation of Alkenes Elimination Reactions Chapter 5 Alkenes Hydrocarbons with C=C bonds Often called “olefins” ( oil forming) “Unsaturated” b double bonds are present – Alk a nes are saturated hydrocarbons Two of the main natural ingredients in citronella oil (insect repellant) α -farnesene found in the waxy coating on apples
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Alkenes in Nature No, it’s not because you smell so sweet. .. http://www.rsc.org/chemistryworld/Issues/2010/September/RepulsiveChemistry.asp
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Synthetic Applications Relying on Alkenes Alkenes
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Alkene Nomenclature H 2 C CH 2 H 2 C CH CH 3 H 2 C C CH 3 CH 3 ethylene * propylene * isobutylene ethene propene 2-methylpropene Common Name Systematic (IUPAC) Name * Also accepted by IUPAC
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Alkene Nomenclature • Always choose the longest chain that contains both atoms of the double bond. • In naming cycloalkenes, the double bond is located between C1 and C2, and the “1” is usually omitted in the name. • The ring is numbered clockwise or counterclockwise to give the first substituent the lower number. • When numbering, double bonds take precedence over alkyl and halide groups • Hydroxyl groups take precedence over double bonds! • Compounds containing both a double bond and a hydroxyl group are named as alkenols and the chain (or ring) is numbered to give the -OH group the lower number. Br Alkene Nomenclature
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Alkenyl Groups methylene vinyl allyl isopropenyl Alkene Stereoisomers • Remember: No rotation around double bonds • 1,2-disubstituted (and more highly substituted) alkenes can exist in two discreet forms cis and trans
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cis and trans isomers are possible when… – at least one substituent on each double bonded carbon is identical (or analogous) to one substituent on the other carbon cis and trans isomers are not possible when… – either of the double bonded carbons bears two identical substituents Alkene Stereoisomers cis / trans convention is ambiguous when no there are no identical or similar groups on the adjacent C=C carbons Need a less ambiguous convention E and Z notational system is more flexible – Based on atomic number • Higher priority given to substituents with higher atomic number
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This note was uploaded on 12/22/2011 for the course CHEM 3371 taught by Professor Anderson,k during the Fall '08 term at Southern Methodist.

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Chapter 5 - Structure and Preparation of Alkenes...

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