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Chapter 07 Powerpoint

Chapter 07 Powerpoint - Introduction to General and Organic...

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Chapter 7 Alkenes: Structure and Synthesis Dr. David P. Brown Department of Chemistry Introduction to General and Organic Chemistry II
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Chapter 7 2 Functional Group Pi bond is the functional group. More reactive than sigma bond. Bond dissociation energies: C=C BDE 146 kcal/mol C-C BDE 83 kcal/mol Pi bond 63 kcal/mol
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Chapter 7 3 Orbital Description Sigma bonds around C are sp 2 hybridized. Angles are approximately 120 degrees. No nonbonding electrons. Molecule is planar around the double bond. Pi bond is formed by the sideways overlap of parallel p orbitals perpendicular to the plane of the molecule .
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Chapter 7 4 Pi Bonding in Ethylene The pi bond in ethylene is formed by overlap of the unhybridized p orbitals of the sp 2 hybrid carbon atoms. Each carbon has one unpaired electron in the p orbital. This overlap requires the two ends of the molecule to be coplanar.
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Chapter 7 5 Bond Lengths and Angles Hybrid orbitals have more s character. Pi overlap brings carbon atoms closer. Bond angle with pi orbitals increases. Angle C=C-H is 121.7 ° Angle H-C-H is 116. 6 °
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Chapter 7 6 Pi Bond Sideways overlap of parallel p orbitals. No rotation is possible without breaking the pi bond ( 264 kJ/mole ). Cis isomer cannot become trans without a chemical reaction occurring.
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Chapter 7 7 IUPAC Nomenclature Parent is longest chain containing the double bond. -ane changes to - ene . (or -diene, -triene) Number the chain so that the double bond has the lowest possible number. In a ring, the double bond is assumed to be between carbon 1 and carbon 2. =>
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Chapter 7 8 Examples: CH 2 CH CH 2 CH 3 CH 3 C CH 3 CH CH 3 CH 3 CHCH 2 CH 3 H 3 C 1-butene 2-methyl-2-butene 3-methylcyclopentene 2- sec -butyl-1,3-cyclohexadiene 3- n -propyl-1-heptene =>
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Chapter 7 9 Examples: Et Br 1,4-Cycohexadiene 2-Ethyl-1,3-cyclohexadiene 5-Bromo-1,3-cyclohexadiene
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Chapter 7 10 Alkene as Substituents = CH 2 methylene (methylidene) - CH = CH 2 vinyl (ethenyl) - CH 2 - CH = CH 2 allyl (2-propenyl) Vinyl benzene
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Chapter 7 11 Examples: OH Br Vinyl alcohol Allyl bromide 3-Methylene cyclohexene
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Chapter 7 12 Common Names Usually used for small molecules. Examples: CH 2 CH 2 ethylene CH 2 CH CH 3 propylene CH 2 C CH 3 CH 3 isobutylene
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Chapter 7 13 A correct IUPAC name for the following compound is: A) 4-Ethyl-2-methyl-4-pentene B) 2-sec -Butyl-1-butene C) 2-Isobutyl-1-butene D) 2-Ethyl-4-methyl-1-pentene E) 2-Methyl-4-methylenehexane Question
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Chapter 7 14 Cis-trans Isomerism Similar groups on same side of double
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