Ch. 5
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| physical properties of alkenes | mp and bp increase with increasing molecular weight. Trans-alkenes generally have higher mp than cis because they are more symmetric which allows for better packing. trans tend to have lower bp than cis because they are less polar
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| polarity | result of an asymmetric distribution in a molecule. has partially positive and partially negative region. dipole points from electropositive alkyl to electronegative alkene
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| common method of synthesizing alkenes | elimination reaction of either alcohols or alkyl halides
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| E1 | 2-step process and the reaction rate depends on the concentration of only the substrate.
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| Step 1 of E1 rxn | departure of leaving group and formation of carbocation intermediate
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| Step 2 of E1 rxn | a proton on an adjacent carbon (the B-carbon) is removed by a weak base, and the double bond is formed with electrons from the now broken carbon-hydrogen bond
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| factors that favor E1 | polar protic solvents, the ability to form a stable carbocation, highly branched carbon chains, good leaving groups, and the absence of a good nucleophile.
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| E2 | rate depends on the substrate and nucleophile. a strong base removes a proton, a halide ion anti to the proton leaves, resulting in the formation of a double bond. produces either cis or trans
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| ways to control E2 vs Sn2 | 1. steric hindrance is important in E2 rxns. 2. a stronger base favors E2 over Sn2, Sn2 is favored over E2 by weak lewis bases (strong nucleophiles)
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| controlling Sn1 vs E1 | done by controlling conditions, specifically polarity of solvent and temperature.
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| redox rxn and H | if a species is reduced it will be getting more hydrogen, if it is oxydized it will be losing hydrogen, and thus gaining double bonds and, often oxygen
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| catalytic hydrogenation | reducing an alkene by adding molecular hydrogen to the double bond with the aid of a metal catalyst. Added on same face of double bond, syn addition
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| Markovnikov's rule | the addition of a group to the more substituted carbon of a double bond. Does this because the more stable carbocation intermediate(the more highly substituted) will form in the slowest step and the nucleophile then attack +charge in fast rxn 2nd step
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| addition of water | double bond is protonated according to Markovnikov's rule, forming the most stable carbocation. Carbocation reacts with water, yielding a protonated alcholol, which then loses a proton to become and alcohol. must be performed at low temp
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| Free radical additions | Occurs in the presence of peroxides, oxygen, or UV light. disobeys Markovnikov rule because X adds first to the double bond, producing most stable free radical. Halogen ends up on least substituted carbon
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| what characterizes a mild or weak reaction | cold, basic, dilute (such as adding alcohols to a double bond)
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| what characterizes rigorous or strong reactions | hot, acidic (breaking the double bond altogether and forming carboxylic acids)
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| peroxycarboxylic acids | are strong oxidizing agents that can oxidize alkenes. products are epoxides (also called oxiranes) syn addition
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| polymerization | creation of long, high-molecular weight chains(polymers) composed of repeating subunits(monomers). usually occurs through a radical mechanism, but anionic and even cationic polymerization commonly observed.
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| alkynes | hydrocarbons that possess one or more C-C triple bonds. all triple bonds form straight lines with 180 between carbons as a result of the sp hybridization
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