Orgo 11.9-11.14

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  1. __ is often the best reagent for converting an alcohol to an alkyl chloride. The byproducts (__) leave the reaction mixture and ensure there can be no reverse reaction. 

    Under the proper conditions, __ reacts by the interesting mechanism:

    Step one?
    Step two?
    • thionyl chloride (SOCl2) 
    • SO2 and HCl
    • 1) the nonbonding electrons of the hydroxyl oxygen atom attack the electrophilic sulfur atom of thionyl chloride; a chloride ion is expelled and a proton is lsot to give a chlorosulfite ester
    • 2) the chlorosulfite ester ionizes and the sulfur atom quickly delivers chloride to the carbocation. When R is primary, chloride probably bonds to carbon at the same time that C-O is breaking
  2. This mechanism resembles the __, except that the nucleophile is delivered to the __ by the __, usualy giving __. 

    Dehydration requires what? Loss of water, followed by loss of a proton, gives the __. An __ is established between reactants and products.
    • Sn1
    • carbocation
    • LG
    • retention of configuration

    an acidic catalyst to protonate the hydroxyl group of the alcohol and convert it to a good LG

    • alkene
    • equilibrium
  3. To drive equilibrium of acid-catalyzed dehydration to the right, we do what?

    Alcohol dehydrations generally take place through the __>
    remove one or both products as they form, either by distilling the products out of the reaction mixture or by adding a dehydrating agent to remove water

    E1 mechanism
  4. E1 dehydration of an alcohol
    Step one is a __, followed by an __ A __ gives the alkene. Because the Rate limiting step is __, the ease of dehydration follows from the ease of formation of carbocations: __. __ are comon.
    • mildly exothermic protonation
    • endothermic, rate-limiting ionization
    • formation of a carbocation
    • 3>2>1
    • rearrangements
  5. With primary alcohols, __ and _ of the  products are so common that __ is rarely a good method for converting them to alkenes.
    • rearrangements
    • isomerization
    • acid-catalyzed dehydration
  6. Review the utility of dehydration adn give guidelines for predicting the products
    • 1) dehydration usually goes by the E1 mechanism. Rearrangements may occur to form more stable carbocations
    • 2) dehydration works best with tertiary alcohols and almost as well with secondary alcohols. Rearrangements and poor yields are common with primary alcohols
    • 3) (Zaitsev's rule) if two or more alkenes might be formed by deprotonation of the carbocation, the more subbed alkene usually predominates
  7. In some cases, a protonated primary alcohol may be attacked by another molecule of __ and udergo an __. The net reaction is a __ to form an __. 

    This __ is a type of __, a reaction that joins two (or more) molecules, often with the loss of a small molecule such as water. This method is used for the __ and __. Under the acidic dehydration conditions, two reactions compete __ competes with __.
    • alcohol 
    • Sn2 displacement
    • bimolecular dehydration
    • ether
    • bimolecular dehydration of alcohols
    • condensation
    • industrial synthesis of diethyl ether and dimethyl ether
    • elimination
    • substitution
  8. How can we control these two competing reactions? 

    The __ shows two molecules of alcohol giving two product molecules: one of __ and one of __. The elimination shows one molecule of alcohol giving two molecules: one of __ and one of __.
    • ether synthesis (substitution)
    • diethyl ether
    • water
    • ethylene
    • water
  9. The elimination results in an increase in the number of molecules and therefore an __ of the system. The elimination has a more __ in __ than the substitution, and the __ in the __ becomes more favorable for the elimination as the temperature increases. __ is favored around 140 degrees Celsius and below, and __ is favored around 180 degrees Celsius and above. Diethyl ether is produced industrially by heating __ with an acidic catalyst at around 140 degree Celcius
    • increase n the randomness
    • positive change 
    • entropy
    • -TdS term
    • Gibbs free energy
    • Sub
    • Elim
  10. The __ is formally a dehydration. The reaction is acid catalyzed and the first step __. Loss of water gives a __. Migration of a __ places the positive charge on the carbon atom bearing the second __ group, where oxygen's nonbonding electrons help to stabilize the positive charge through __. This extra stability is the driving force for the __, which converts a relatively stable __ into an even better __. Deprotonation of the __ gives the product, __.
    • pinacol rearrangement
    • is protonation of one of the hydroxyl groups
    • tertiary carbocation
    • methyl group
    • -OH group
    • resonance
    • rearrangement
    • tertiary carbocation
    • resonance stabilized carbocation
    • resonance-stabilized cation
    • pinacolone
  11. __ are common in acid-catalyzed reactions of diols. One of the hydroxyl groups protonates and leaves as water, forming a __. __ gives a resonance0stabilized cation with the remaining __ helping to stabilize the positive charge.
    • pinacol-like rearrangements
    • carbocation
    • rearrangement
    • hydroxyl group
  12. __ are cleaved by __. The produts are the ame __ and __ that would be formed by __. )) followed by __ serves as a useful alternative to __, and the __ by itself is useful for determining the structures of sugars.

    __ probably involves a __ intermediate.
    • 1,2-diols (glycols)
    • periodic acid
    • ketones
    • aldehydes
    • ozonolysis-reduction of the alkene
    • dihydroxylation
    • periodic acid cleavage
    • ozonolysis
    • periodate cleavage
    • periodic acid cleavage of a glycol
    • cyclic periodate intermidate
  13. To an organic chemist, the term __ normally means an ester of a carboxylic acid unless some other kind of ester is specified. Replacing the -OH group of a carboxxylic acid with the -OR group of an alcohol gives a __. The __ shows the relationship between the alcohol and the acid on the left and the ester adn water on the right.
    • ester
    • carboxylic ester
    • Fischer esterification
  14. Because the __ is an __, clver techniques are required for good yields.

    Another way to form an ester: An __ reacts with an __ in an exothermic reaction to give an ester.
    • Fischer esterification
    • equilibrium

    • alcohol
    • acid chloride
  15. In addition to forming esters with carboxylic acids, alcohols form __ with inorganic acids. In each type of ester, the __ of the alcohol replaces a __ of the acid with loss of water.
    • inorganic esters
    • alkoxy group
    • hydroxyl group
  16. A __ is like a sulfonate ester, except there is no alkyl group directly bonded to the sulfur atom. In an __, __ are bonded to sulfur through oxygen atoms. __ are excellent leaving groups. Like __, __ are good electrophiles. Nucleophiles react with __ to give alkylated products.
    • sulfate ester
    • alkyl sulfate ester
    • alkoxy groups
    • sulfate ions
    • sulfonate esters
    • sulfate esters x2
  17. __ are formed from alcohols and nitric acid. In __, the __ are the oxidizer and the CH and CH2 groups are the fuel to be oxidized. This intimate association of fuel and oxidizer allows the explosion to proceed at a much faster rate, forming a shock wave that propagates through the explosive and initiates the reaction.
    • nitrate esters
    • nitroglycerine
    • nitro groups
  18. Alkly phosphates are composed of 1 mole of phosphoric acid combined with 1,2, or 3 moles of an alcohol. For example, methanol forms three __.

    We learned ot remove the __ from an alcohol by reduction with an "active" metal such as Na or K. This reaction generates a Na or K salt of an __ and hydrogen gas.
    phosphate esters 

    hydroxyl proton

    alkoxide ion
  19. The reactivity of alcohols toward Na and K decreases in the order __. Sodium reacts quickly with __ and some __. Potassium is more reactive than sodium and is commonly used with __ and some __. Some alcohols react slugglishly with both sodium and potassium. In these cases, a useful alternative is __, usually in tetrahydrofuran solution. __ reacts quickly to form the alkoxide, even with difficult compounds.
    • primary 
    • secondary alcohols
    • tertiary
    • secondary alcohols
    • sodium hydride x2
  20. The __ is a strong nucleophile as well as a powerful base. Unlike the alcohol itself, the __ reacts with __ and __ to form __. This general reaction, called the __, is an __. The __ must be primary so that a back-side attack is not hindered. When the alkyl halide is not primary, __ usually reasults.
    • alkoxide ion x2
    • primary alkyl halides and tossylates 
    • ethers
    • Williamson ether synthesis
    • Sn2 displacement
    • alkyl halide (or tosylate)
    • elimination
  21. Williamson Ether Synthesis: This is the __.
    • most important method for making ethers
    • 1: Form the alkoxide of the alcohol having the more hindered group
    • 2: the alkoxide displaces the leaving group of a good Sn2 substrante
  22. Int he __ the __ must be a good __. In proposing a __ we usually choose the less hindered alkyl group to  be the halide (or tosylate) and hte more hindered gorup to be the alkoxide ion.
    • Williamson ether synthesis
    • alkyl halide (or tosylate) 
    • Sn2 substarte (usually primary)
    • Williamson snyhtesis
Card Set:
Orgo 11.9-11.14
2013-12-25 23:56:46
CHM 202
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