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This 2 page Class Notes was uploaded by Maggie Bruce on Friday October 7, 2016. The Class Notes belongs to CHM 1240 at Wayne State University taught by Stanislav Groysman in Fall 2016. Since its upload, it has received 29 views. For similar materials see Organic Chemistry 1 in Chemistry at Wayne State University.
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Date Created: 10/07/16
Chapter three Alkenes o Ethane – C 2 4 o Hybridization Each carbon is bound to three atoms 2 3 sp orbitals and two 2p orbitals o Shape is planar, 120* o Rotation is not possible because of the double bond 65.9 Kcal/mol is required to break and rotate the double bond Derivatives of alkenes o Vinyl – replacing one hydrogen o Replacing a hydrogen with a methyl group makes propene, or vinyl allyl Isomers of alkenes o Replacing two hydrogens may result in a cis (Z) or trans (E) molecule o If the two most important groups are on the same side it is cis o If the two most important groups are on opposite sides it is trans Nomenclature o The double bond need to be part of the main chain o The suffix is –ene o The chain needs to be numbered so the double bond has the lowest number possible o Polyene Molecule with more than one double bond Diene, triene, tetraene, etc. Cahn-Ingold-Prelog Priority System o Ranks groups attached to the double bonds to decide if the molecule is cis or trans o Rules Use the atomic number of the atoms attached to the double bonds, the higher one wins When the same atom is attached, add up everything that is attached to those atoms Multiple bonds count as multiplied single bonds, so double or triple the atom it is attached to Stability of alkenes o More substitutions means more stability Alkynes o Contain a triple bond o C n 2n-2 o Ethyne is the simplest o 180* o sp hybridization Nomenclature o Triple bond needs to be part of the main chain with the lowest number possible o If there is a double bond and a triple bond, the double bond gets the lowest number, named en-yne Rings o In small rings, double bonds must be cis o Triple bonds can only be in large rings, eight or more Bronsted acidity of alkynes o Hydrocarbons are usually weak bronsted acids o Alkynes are stronger o It is easier to remove a hydrogen from an alkyne than an alkene Degrees of unsaturation o Used for determining the structure of a molecular formula o One pi bond or one ring is one degree of unsaturation o C6H14s fully saturated o One degree of unsaturation means the molecule has two fewer hydrogens than the maximum amount o Formula (2(c+1)-(H+hal-N))/2 Addition reactions of alkenes and alkynes o Nucleophilic attack of pi bond on acid o Forms intermediate carbocation Planar 2 Sp Empty p orbital Tertiary is the most stable, followed by secondary and then primary o Halide attaches to carbocation Energetics of addition reactions o Highly favorable reactions o The pi bond is relatively weak and easy to break o Energy is needed to break the pi bond, but much more energy is released when the halide attaches to the carbocation o deltaH = bonds formed – bonds broken Regiochemistry of addition reactions o Two products are possible o Only one if formed, because the product is much more stable if the halide attaches to a tertiary carbon Hydration o Catalyzed addition of water to alkenes to form alcohols o Three steps Pronation of alkene, forms carbocation Addition of water to carbocation, forms oxonium + Depronation of the oxonium, forms H O3 o Hydronium is a catalyst so it is regenerated o Regioselective reaction Hydroxide will only bond to the more stable tertiary carbon
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