Orgo Ch 6.11-6.

Card Set Information

Orgo Ch 6.11-6.
2013-10-29 17:28:42
CHM 201

Show Answers:

  1. An alkyl halide is often referred to as the __: literally, the compound that is being attacked by the reagent. Besides alkyl halides, a variety of other types of compounds serve as _- in __ reactions. To be a good __ for __ attack by a __, a molecule must have an __ with a good __, adn that carbon atom must not be too __ for a __ to attack.
    • solvent
    • solvents
    • SN2
    • solvent 
    • Sn2
    • nucleophile
    • electrophilc C atom
    • leaving group
    • sterically hindered
    • nucleophile
  2. A leaving group serves two purposes in the Sn2 reaction?
    • It polarizes the C-X bond, making the carbon atom electrophilic
    • It leaves with the pair of electrons that once bonded it to the electrophilc carbon atom.
  3. To fill these roles, a good leaving gorup should be what?
    • electron withdrawing, to polarize the carbon atom
    • stable (not a strong base) once it has left, and
    • polarizable, to stabilize the transition state
  4. The leaving group must be __ to create a __ on the carbon atom, making the carbon __. An __ leaving gorup also stabilizes the negatively charged transition state.
    • electron withdrawing
    • partial positive charge
    • electrophilic
    • electron-withdrawing leaving group
  5. __ are strongly electronegative, so alkyl halides are common __ for __ reactions. O, N, and S also form strongly __ with carbon; given the right substituents, they can form the basis for excellent __.
    • halogens
    • substrates
    • Sn2
    • polarized bonds
    • leaving groups
  6. The leaving group must be __ once it has left with the pair of electrons that bonded it to carbon. A stable leaving group is needed for __. The leaving group is leaving in the __; a reactive leaving group would do what?
    • stable
    • favorable energetics

    • transition state
    • raise the energy of the transition state, slowing down the reaction
  7. Also, the energy of the leaving group is reflected in the energy of what? 

    A reactive leaving group would raise the energy of the __, driving the equilibrium towards what?
    • the products
    • products
    • reactants
  8. Good leaving groups should be __; therefore, they are the __ of __. The __ are strong, and their conjugates are weak. Other weak bases, such as sulfate ions, sulfonate ions, and phosphate ions, can also serve as good __.
    • weak bases
    • conjugate bases
    • strong acids
    • hydrohalic acids (HCl, HBr, HI)
    • leaving groups
  9. __, __ and other strong bases are poor leaving groups for Sn2 reactions

    When can a neutral group be a good leaving group? An example.
    The need to protonate alcohols limits the choice of nucleophiles to those few that are ?
    • hydroxide ion
    • alkoxide ions

    • when it leaves from a positively charged species
    • water
    • weak bases
  10. Finally, a good leaving group should be __. Why?
    • polarizable
    • to maintain partial bonding with the carbon atom in the transition state
  11. This bonding helps __ the __ and reduce the __.
    The departure of a leavving group is like the attack of a nucleophile, except hta tthe bond is __, not __.
    • stabliize
    • transition
    • Ea
    • breaking
    • forming
  12. Polrizing nucleophiles and polarizable leaving groups both stabilize the __ by engagin gin more bonding at a longer distance. __, one of the most polarizable ions, is both a good nucleophile and a good leaving group. __, however, is a hard ion.
    • transition state
    • iodide ion
    • fluoride
  13. True or False:
    All alkyl groups undergo Sn2 reactions at the same rate.

    What is the most important factor in its reactivity towards Sn2 displacement?
    • False: differnet rates
    • the structure of the substrate
  14. The reaction goes rapidly with __ and with most __. It is slower with __. __ fail to react at all by the Sn2 mechanism.
    • methyl halides
    • primary halides
    • secondary halides
    • tertiary halides
  15. All slow-reacting compounds have one property in common: what
    • the back side of the electrophilic carbon atom is crowded by the presence of bulky groups. 
    • tertiary halides are more hindered than secondary halides, which are more hindered than primary halides
  16. Even a bulky primary halide undergoes __ reaction at a rate similar to that of a tertiary halide. The relative rates show that it is the bulk of the __, rather than an electronic effect, that hinders the reactivity of __ in the __ displacement.
    • Sn2
    • alkyl groups
    • bulky alkyl halides
    • Sn2
  17. This effect on the rate is another example of __. When the nucleophile approaches the back of the __, it must come within bonding distance of hte __ of the C-X sp3 orbital. If there are two alkyl groups bonded to the carbon attom, this process is difficult. __ make it impossible. Just one can produce a large amount of __ if it is unusually bulky.
    • electrophilic carbon atom
    • back lobe
    • three alkyl groups
    • steric hindrance
  18. The Sn2 reaction requires what?
    attack by a nucleophile on the back side of an electrophilic carbon atom
  19. A carbon atom can have only __, so the leaving group must leave as the __ bonds ot the carbon atom. The nucleophile's electrons intsert into the __ of carbon's sp3 hybrid orbital in its __ combo with the orbital of the leaving gorup because the bonding MO is already filled.
    • four filled bonding orbitals
    • nucleophile
    • back lobe
    • anticbonding combination
  20. The transition state shows what?
    partial bonding to both the nucleophile and the leaving group
  21. __ literally turns the tetrahedron on the carbon atom inside out. In the product, the nucleophile assumes a __ position opposite the position the leaving gorup originally occupied. We call this an __ at the C atom.
    • back-side attack
    • stereochemical position
    • inversion of configuration
  22. In the case of an __, __ gives the opposite configuration of the carbon atom. The __ is the most common example of a __, a step where an asymmetric carbon atom undergoes inversion of cionfiguration.
    • asymmetric C atom
    • back-side attack
    • Sn2 displacement
    • Walden inversion
  23. In some cases, __ of configuration is readily apparent. 
    The Sn2 dsplacement is a good example of a __: one in which different stereoisomers reaect to give different stereoisomers of the product.
    • inversion 
    • stereospecific reaction