Chapter06- Alkenes- Structure and Reactivity

Chapter06- Alkenes- Structure and Reactivity - 6 Alkenes...

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6. Alkenes: Structure and Reactivity Based on McMurry’s Organic Chemistry , 6 th edition ©2003 Ronald Kluger Department of Chemistry University of Toronto
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McMurry Organic Chemistry 6th edition Chapter 6 2 Alkene - Hydrocarbon With Carbon- Carbon Double Bond Also called an olefin but alkene is better Includes many naturally occurring materials Flavors, fragrances, vitamins Important industrial products These are feedstocks for industrial processes
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McMurry Organic Chemistry 6th edition Chapter 6 3 6.2 Degree of Unsaturation Relates molecular formula to possible structures Degree of unsaturation: number of multiple bonds or rings Formula for saturated a acyclic compound is C n H 2n+2 Each ring or multiple bond replaces 2 H's
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McMurry Organic Chemistry 6th edition Chapter 6 4 Example: C 6 H 10 Saturated is C 6 H 14 Therefore 4 H's are not present This has two degrees of unsaturation Two double bonds? or triple bond? or two rings or ring and double bond H 3 CC C C C CH 3 H H H H H H H H
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McMurry Organic Chemistry 6th edition Chapter 6 5 Degree of Unsaturation With Other Elements Organohalogens (X: F, Cl, Br, I) Halogen replaces hydrogen C 4 H 6 Br 2 and C 4 H 8 have one degree of unsaturation Oxygen atoms - if connected by single bonds These don't affect the total count of H's
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McMurry Organic Chemistry 6th edition Chapter 6 6 Compounds with the same degree of unsaturation can have many things in common and still be very different Degree of Unsaturation and Variation
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McMurry Organic Chemistry 6th edition Chapter 6 7 If C-N Bonds Are Present Nitrogen has three bonds So if it connects where H was, it adds a connection point Subtract one H for equivalent degree of unsaturation in hydrocarbon
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McMurry Organic Chemistry 6th edition Chapter 6 8 Count pairs of H's below CnH2n+2 Add number of halogens to number of H's (X equivalent to H) Don't count oxygens (oxygen links H) Subtract N's - they have two connections Summary - Degree of Unsaturation
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McMurry Organic Chemistry 6th edition Chapter 6 9 6.3 Naming of Alkenes Find longest continuous carbon chain for root Number carbons in chain so that double bond carbons have lowest possible numbers Rings have “cyclo” prefix
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McMurry Organic Chemistry 6th edition Chapter 6 10 Many Alkenes Are Known by Common Names Ethylene = ethene Propylene = propene Isobutylene = 2- methylpropene Isoprene = 2-methyl-1,3- butadiene
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McMurry Organic Chemistry 6th edition Chapter 6 11 6.4 Electronic Structure of Alkenes Carbon atoms in a double bond are sp 2 -hybridized Three equivalent orbitals at 120º separation in plane Fourth orbital is atomic p orbital Combination of electrons in two sp 2 orbitals of two atoms forms σ bond between them Additive interaction of p orbitals creates a π bonding orbital Subtractive interaction creates a π anti-bonding orbital Occupied π orbital prevents rotation about σ -bond Rotation prevented by π bond - high barrier, about 268 kJ/mole in ethylene
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