Orgo 9.8-9.16

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  1. In some cases, we can generate a carbon-carbon triple bond by eliminating two molecuels of __ from a __. __ of a __ or __ gives a __. Under strongly basic conditions, a second __ may occur to form an alkyne.
    • HX
    • dihalide
    • dehydrohalogenation
    • geminal
    • vicinal dihalide
    • vinyl halide
    • dehydrohalogenation
  2. The second __ occurs only under extremely basic conditions. Uing either KOH or sodium amide at elevated temps imples brutal reaction conditions, encouraging __ and __. __ are often poor.
    • dehydrohalogenation
    • side reactions and rearrangements
    • yields
  3. The __ of acetylide ions on __ is one of the best methods for making more complicated  alkynes. 

    Many of the reactions of alkynes are similar to the corresponding rxns of __ because both involve __ between two carbon atoms.
    • nucleophilic attack
    • electrophiles
    • alkenes
    • pi bonds
  4. Like the pi bond of the alkene, the pi bonds of an alkyne are __, and they readily undergo __. The bond energy of the alkyne triple bond is only about __ more than the bond energy of an alkene. This is the energy needed to break one of the pi bonds of an alkyne.
    • electron rich
    • addition reactions
    • 226 kJ (54 kcal)
  5. Reagents add across the __ of alkynes just the same as double bonds. In effect, this reaction converts a __ of the alkyne and a __ of the reagent into two new __. Since __ are generally stronger than __, the rxn is usually __. ALkynes have two __, so up to two molecules can add across the __, depending on the reagents and conditions.
    • triple bond
    • pi bond 
    • sigma bond 
    • sigma bonds
    • sigma bonds
    • pi bonds
    • exothermic
    • pi bonds
    • triple bond
  6. We must consider the possibility of a __ whenever a reagnet adds across the __ of an alkyne. Some conditions may allow the reaction to stop after a __, while other conditions give __.
    • double addition
    • triple bond 
    • single addition
    • double addition
  7. Catalytic Hydrogenation to Alkanes 

    In the presence of a suitable __, hydrogen adds to an alkyne, reducing it to an __. What are some catalysts?

    Catalytic hydrogenation takes place in __ , with an __. With efficient catalysts such as __(3)__, it is usually what?
    • catalyst
    • alkane
    • platinum
    • palladium
    • nickel

    • two stages
    • alkene intermediate

    • platinum
    • palladium
    • nickel
    • impossible to stop the rxn after the alkene stage
  8. Catalytic Hydrogenation to cis Alkenes
    Hydrogenation of an alkyne can be stopped at the __ by using a __ made by treating a good catalyst with a compound that makes the catalyst __. 

    __ is a poisoned palladium catalyst, composed of powdered barium sulfate coated with palladium, poisoned with quinoline.
    • alkene stage
    • "poisoned catalyst"
    • less effective
    • Lindlar's catalyst
  9. __ is a newer alternative to __ that is more easily made and often gives better yields. The catalytic hydrogenation of alkynes is similar to hydrogenation of alkenes, and both proceed with __. 

    In catalytic hydrogenation, the face of a pi bond contacts the __, and teh catalyst does what, allowing two hydrogens to __.

    This simultaneous (or nearly simultaneous) addition of two hydrogen on __ ensures __.
    • Nickel boride
    • Lindlar's catalyst

    • syn stereochemistry
    • solid catalyst
    • add

    • the same face
    • syn stereochemistry
  10. To form a trans alkene, trans hydrogens must be added to the alkyne with __. 

    __ in __ reduces alkynes with __, so this reduction is used to convert alkynes to __.
    • anti steroeochemistry
    • sodium metal
    • liquid ammonia
    • anti stereochemistry
    • trans alkenes
  11. __ is a gas at room temp, but it is kept liquid by using dry ice to cool the reaction vessel. As sodium dissolves in liquid ammonia, what does it do, which does what? It is these __ that actually reduce the alkyne.
    • ammonia
    • gives up electrons
    • produces a deep blue color
    • solvated electrons
  12. The __ proceeds by addition of an electron to the alkyne to form a __, followed by __ to give a __. Protons are provided by the __ or by an __added as a __. Addition of another electron, followed by another proton, givse the product.
    • metal-ammonia reduction
    • radical anion
    • protonation
    • neutral radical
    • ammonia solvent
    • alcohol 
    • cosolvent
  13. Mechanism:
    Metal-Ammonia Reduction of an Alkyne: This mechanism involves addition of __, followed by __, then addition of __, followed by __.
    • an electron
    • a proton
    • a second electron
    • a second proton
  14. Mechanism:
    Metal-Ammonia Reduction of an Alkyne: Steps
    • 1) An electron adds to the alkyne, forming a radical anion
    • 2) The radical anion is protonated to give a radical
    • 3) An electron adds to the radical, forming an anion
    • 4) Protonation of the anion gives an alkene
  15. The __ of the __ appears to resuult from the greater __ of the __ in the __ configuration, where the alkyl groups are farther apart. An electron is added to the __ to give a __, which is quickly protonated to the __.
    • anti stereochemistry
    • sodium-ammonia reduction
    • stability
    • vinyl radical
    • trans
    • trans radical
    • trans vinyl anion
    • trans alkene
  16. Bromine and chlorine add to alkynes the same way as they do to alkenes. If one mole of halogen adds to one mole of an alkyne, th product is a __. The stereochemistry of addition may be either __  or __, and the products are often mixtures of __ and __ isomers.
    • dihaloalkene
    • syn 
    • anti
    • cis
    • trans
  17. If two moles of halogen add to one mole of alkyne, a __ results. Sometmes, it is difficult to keep the reaction from proceeding all the way to the __ even when we want it to stop at the __.
    • tetrahalide x2
    • dihalide
  18. `__ add across the triple bond of an alkyne in much the same way they add across the alkene double bond. The initial product is a __. When a hydrogen halide adds to a __, the prouct has the orientation predicted by __. A second molecule of HX can add, usually with the same orientation as the first.
    • hydrogen halides
    • vinyl halide
    • terminal alkyne
    • Markovnikovs rule
  19. The mechanism is similar to the mechanism of hydrogen halide addition to alkenes. The __ formed int he first step is more stable with the positive charge on the __ carbon atom. Attack by halide ion completes the reaction.
    • vinyl cation
    • more highly subbed
  20. When 2 moles of a hydrogen halide adds to an alkyne, the second mole usually adds with the same orientation as the first. This consistent orientation leads to a __. 

    __ catalyzes a __ that adds HBr across the double bond of an alkene in an __ sense. A similar rxn occurs with alkynes, with HBr adding with __.
    geminal dihalide

    • peroxide
    • free-rad chain rxn
    • anti Mark x2
  21. Alkynes undergo __ across the triple bond in the presence of __ as a catalyst.
    A mixture of __ in __ is commonly used as the reagent. The hydration of alkynes is similar to that of alkenes, and it also goes with __. The products are not the products we'd expect, however. 
    Electrophilic addition of __ gives a __, which reacts with water and loses a proton to give an __.
    Under the acidic reaction conditions, mercury is replaced by hydrogen to give a __, called an __.
    • acid-catalyzed addition of water
    • mercuric ion
    • mercuric sulfate
    • aqueous sulfuric acid
    • Mark addition
    • mercuric ion
    • vinyl cation
    • organomercurial alcohol
    • vinyl alcohol 
    • enol
  22. __ tend to be unstable and isomerize to the __ form. This isomerization involves the shift of a proton and a double bond. The __ is lost, and a proton is regained at the methyl position, while the __ shifts from the C=C position to the C=O position. This type of rapid equilibrium is called a __. The one shown is the __. The __ form usually predominates.
    • enols
    • ketone
    • hydroxyl proton
    • pi bond
    • tautomerism
    • keto-enol tautomerism
    • keto
  23. In acidic solution, the __ takes place by addition of a proton to the adjacent carbon atom, followed by loss of the __ proton from oxygen.
    • keto-enol tautomerism
    • hydroxyl
  24. Acid- Catalyzed Keto Enol Tautomerism: Under acidic conditions, what happens? 

    the proton first adds at its new position on the adjacent carbon atom, and then is removed from its old position in the hydroxyl group

    • Step 1: Addition of a proton at the methylene group
    • 2: Loss of the hydroxyl proton
  25. In hydroboration of an alkene, a hindered __ must be used to prevent __ across the triple bond. __, called __. adds to the triple bond only once to give a __. (__ is an older common name for pentyl). In a __, the boron bonds to the terminal carbon atom.
    • dialkylborane
    • addition of two molecules of boron
    • di(secondary isoamyl)borane
    • disiamylborane
    • vinylborane
    • amyl
    • terminal alkyne
  26. Oxidation of the __ (usuing basic hydrogen peroxide) gives a __, resulting from __ addition of water across the triple bond. This __ quickly tautomerizes to its more stable carbonyl __ form. In the case of a terminal alkyne, the __ is an __. This sequence is an excellent method for converting __ to __.
    • vinylborane
    • vinyl alcohol (enol)
    • anti-Mark 
    • enol
    • (keto)
    • keto product
    • aldehyde
    • terminal alkynes
    • aldehydes
  27. Under basic conditions, the __ operates by a different mechanism than it does in acid. In base, the proton is first removed from its old position in the OH group, and then replaced on carbon. In acid, the proton was first added on carbon, and then removed from the hydroxyl group.
    keto-enol tautomerism
  28. Base-Catalyzed Keto-Enol Tautomerism:
    Under basic conditions, the proton is first removed from its old position in the __, and then replaced in its new position on the adjacent carbon atom of the __ or __.
    • enol
    • aldehyde
    • ketone
    • 1: Loss of the hydroxyl proton
    • 2: Reprotonation on the adjacent carbon atom
  29. Under mild conditions, potassium permanganate oxidizes alkenes to __, compounds with two =OH groups on adjacent carbon atoms. This oxidation involves adding a __to each end of the double bond (__).
    • glycols
    • hydroxyl group
    • hydroxylation
  30. A similar reaction occurs in alkynes. If an alkyne is treated with cold, aqueous potassium permanganate under nearly __ conditions, an __ results. This is conceptually the same as __ each of the two pi bonds of hte alkyne, then losing two molecules of water to give the __.
    • neutral
    • alpha-diketone
    • hydroxylating
    • diketone
  31. __ probably give a __ at first, but the __ quickly oxidizes to an acid under these conditions.
    • terminal alkynes
    • keto-aldephyde
    • aldehyde
  32. If the rxn mixtures becomes warm or too basic, the __ undergoes __. The products are the __ of __, which can be converted to the free acids by adding dilute acid.
    • diketone
    • oxidative cleavage
    • carboxylate salts
    • carboxylic acids
  33. __ are cleaved similarly to give a carboxylate ion and formate ion. Under these oxidizing conditions, formate oxidizes further to __, which becomes CO2 after protonation.
    • terminal alkynes
    • carbonate
  34. __ of an alkyne, followed by __,, cleaves the triple bond and gives two __. Eather __ or __ can be used to determine the position of the triple bond in an unknown alkyne.
    • ozonolysis
    • hydrolysis
    • carboxylic acids
    • permanganate cleavage 
    • ozonolysis
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Orgo 9.8-9.16
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