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MCAT O-Chem

Ch. 5

QuestionAnswer
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
polarity result of an asymmetric distribution in a molecule. has partially positive and partially negative region. dipole points from electropositive alkyl to electronegative alkene
common method of synthesizing alkenes elimination reaction of either alcohols or alkyl halides
E1 2-step process and the reaction rate depends on the concentration of only the substrate.
Step 1 of E1 rxn departure of leaving group and formation of carbocation intermediate
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
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.
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
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)
controlling Sn1 vs E1 done by controlling conditions, specifically polarity of solvent and temperature.
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
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
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
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
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
what characterizes a mild or weak reaction cold, basic, dilute (such as adding alcohols to a double bond)
what characterizes rigorous or strong reactions hot, acidic (breaking the double bond altogether and forming carboxylic acids)
peroxycarboxylic acids are strong oxidizing agents that can oxidize alkenes. products are epoxides (also called oxiranes) syn addition
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.
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
Created by: adam87 on 2010-07-02



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