Orgo Ch 6.7-6.10

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Orgo Ch 6.7-6.10
2013-10-27 12:33:37
CHM 201

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  1. Alkyl halides are easily converted to many other functional groups. The halogen atom can leave with its bonding pair of electrons to form a stable __; we say that a halide is a good __.
    • halide ion
    • elaving group
  2. When another atom replaces the halide ion, the reaction is a __. When the halide ion leaves another atom or ion and forms a new pi bond, the reaction is an __. In many __, a molecule of H-X is lost from the alkyl halide to give an alkene. These __ are called __ because a hydrogen halide has been removed from the alkyl halide. __ and __ reactions often compete with each other.
    • substitution
    • elimination 
    • eliminations
    • eliminations
    • dehydrohalogenations
    • substitution and elimination
  3. In a __, a nucleophile replaces a __ from a carbon atom, using its lone pair of electrons to form a new bond to the carbon atom. 

    In an __, both the halide ion and another substituent are lost. A new __ is formed.
    • nucleophilic substitution 
    • leaving group
    • elimination
    • pi bond
  4. In the __, the reagent reacts as a __, abstracting a __ from the alkyl halide. Most _ are also basic and can engage in either __ or __, depending on the __ and the reaction conditions.
    • elimination (a dehydrohalogenation)
    • base
    • proton
    • nucleophiles
    • substitution or elimination
    • alkyl halide
  5. Besides __, many other types of compounds undergo __ and __ reactions.
    • alkyl halides
    • substitution 
    • elimination
  6. hydroxide ion is a strong __ (donor of an electron pair) because the oxygen atom has unshared pairs of electrons and a negative charge. 

    __ is called the __, meaning the compound that is attacked by the reagent. The carbon atom of __ is __ because it is bonded to an __.
    • nucleophile
    • iodomethane
    • substrate
    • iodomethane
    • electrophilic
    • electronegative iodine atom
  7. __ is drawn away from carbon by the halogen atom, giving the carbon atom a __. The __ is attracted to this __.
    • electrond ensity
    • partial positive charge
    • negative charge of hydroxide ion 
    • partial positive charge
  8. Hydroxide ion attacks the backside of the __ carbon atom, donationg a pair of electrons to form a new bond.
    electrophilic carbon
  9. Carbon can accommodate only eight electrons in its valence shell, so what must happen?

    Iodine ion is the __. Why?
    the carbon-iodine bond must begin to break as the carbon-oxygen bond begins to form

    • leaving group
    • it leaves with the pair of electrons that once bonded it to the carbon atom
  10. What does SN2 stand for?

    What does the third term mean?
    • substitution, nucleophilic, bimolecular
    • bimolecular means that the transition state of the rate-limiting step involves the collision of two molecules.
  11. Bimolecular reactions usually have __.
    rate equations that are second order overall
  12. The __ reaction of methyl iodide with hydroxide ion is a __, taking place in a single step with bonds __ and __ at the same time. THe middle structure is a __, a point of max energy, rather than an __.In this __, the bond to the __ is partially formed, adn the bond to the __ is partially broken.
    • Sn2 reaction
    • concerted reaction
    • breaking and forming
    • transition state
    • intermediate
    • transition state
    • nucleophile 
    • leaving group
  13. The reaction energy diagram for the substitution sows one?
    The reactants are shown slighly __ in energy than the products beacuse this reaction is known to be __. The transition state is much __ in energy because it involves a __ with __.
    only one transition state and no intermediates between the reactants and the products

    • higher
    • exothermic
    • higher
    • five-coordinate carbon atom
    • two partial bonds
  14. Explain the Sn2 Reaction.
    takes place in a single (concerted) step. A strong nucleophile attacks the electrophilic carbon, forcing the leavinggroup to leave
  15. The Sn2 reaction provides a useful method for synthesizing __ and __, which are more difficult to make than __ and __. Halides can be coverted to other halides by __, in which one halide displaces another.
    • alkyl iodides and fluorides
    • alkyl chlorides and bromides
    • halogen exchange reactions
  16. __ is a good nucleophile, and many other alkyl chlorides react with sodium iodide to give alkyl iodides.
  17. A stronger __ is an ion or molecule that reacts faster in the Sn2 reaction than a "weaker" __ under the same conditions. A strong __ is much more effective than a weak one in attacking an __ carbon atom.
    • nucleophile x3
    • electrophile
  18. __ has nonbonding electrons that are readily available for bonding. In the transition state, the negative charge is shared by the oxygen of __ and by hte __.
    • methoxide ion
    • methoxide
    • halide leaving group
  19. __, however, has no negative charge; the transition state has a __ on the halide but a __ on the methanol oxygen aton.
    • methanol
    • partial negative charge
    • partial positive charge
  20. We can generalize the case of methanol and methoxide ion to say what?
    a base is always a stronger nucleophile than its conjugate acid
  21. True or False
    Nucleophilicity and basicity are synonymous terms.
    • False
    • Basicity is defined by the equilibrium constant for abstracting a proton
    • nucleophilicty is defined by the rate of attack on an electrophilic carbon aton
  22. In both cases, the __ forms a new bond. If the new bond is to a proton, it has reacted as a __; if the new bond is to carbon, it has reacted as __. Predicting which way a species will react may be difficult; most (but not all) good __ are also strong __, and vice versa.
    • nucleophie (or base)
    • base
    • nucleophile
    • nucleophiles 
    • bases
  23. Trends in nucleophilicity
    a species with a negative charge is a stronger nucleophiel than a similar neutral species. In particular a base is a stronger nucleophile than its conjugate acid
  24. Trends in nucleophilicity
    nucleophilicty decreases from left to right in the periodic table, following the increase in electronegativity from left to right. The more electronegative elements have more tightly held nonbonding electrons that are less reactive toward forming new bonds
  25. Trends in nucleophilicity
    Nucleophilicity incresaes donw the periodic table, following the increase in size andpolarizability, and the decrease in electronegativity
  26. The third trend (__) reflects an atom's ability to engage in partial bonding as it begins to attack an __. As we go down the PT, the atoms become larger, with more electrons at greater distances fromt he nucleus. The electrons are more loosely held, adn the atom is more __: Its electrons can move more freely toward a positive charge, resulting in stronger bonding int he __. The increased mobility of its electrons enhances hte aton's ability to form a bond at a relatively long distance
    • size and polarizability
    • electrophilic carbon atom
    • polarizable
    • transition state
  27. __ is a "hard" (__) nucleophile, and its nucleus must approach the carbon nucleus quite closely before the elctrons can begin to overlap and form a bond. In the __, there is little bonding between F and C.
    • fluoride
    • low-polarizability
    • transition state
  28. In contrast, the outer shell of the iodide ion is the fifth shell. These electrons are loosely held, making the iodide ion a "soft" __ nucleophie. THe outer electrons begin to shift and overlap with the carbon atom from farther away. There is a great deal of bonding between iodine and carbon int he transition state, which __ the energy of the TS.
    • high-polarizability
    • lowers
  29. To serve as a nucleophile, an ion or molecule must do what? 
    What hinders this, causing a slowing of the reaction rate?
    When __ interfere with a reaction by virtue of their size, it is called __.
    • get in close to a carbon atom to attack it
    • bulky groups on the nucleophile
    • bulky groups
    • steric hindrance
  30. __ has little effect on __ because __ invovles attack on an unhindered proton.
    When a __ attacks a carbon atom, however, a bulky __ cannot approach the C atom so easily. Most __ are also __, capable of attacking either a proton or an electrophilic carbon atom.
    If we want a species to act as a base, what do we do?
    If we want a species to act as a nucleophile, what do we do?
    • steric hindrance
    • basicity x2
    • nucleophile x2
    • nucleophiles
    • bases
    • use a bulky reagent
    • use a less hindered reagent
  31. Another factor affecting the nucleophilicity of these ions is their __, particularly in __. A __ is one that has acidic protons, usually in the form of O-H or N-H groups. These groups form H bonds to negatively charged __.

    __, especially alcohols, are convenient solvents for __ because the reagents tend to be quite __.
    • solvation
    • protic solvents x2
    • nucleophiles

    • protic solvents
    • nucleophilic substitutions
    • soluble
  32. __ are solvated more strongly than __ in a __ becaause the solvent approaches a __ more closely and forms stronger __. 

    When an anion reacts as a __, energy is __ to __ some of the solvent molecules, breaking some of the hydrogen bonds that stabilized the solvated anion. __ energy is required to __ solvent from a __ such as flouoride than from a __ ion like iodide.
    • nucleophile
    • required
    • strip off
    • more
    • strip off
    • small, strongly solvated
    • large, diffuse, less strongly solvated
  33. The enahnced solvation of smaller anions in __, requiring more energy to strip off heir solvent molecules, reduces their __..
    • protic solvents
    • nucleophilicity
    • polarizability
  34. This trend reinforces the trend in __: (explain trend)
    the polarizability incresaes with increasing atomic number and the solvation energy (in protic solvents) decreases with increasing atomic number. Therefore, nucleophilicity (in protic solvents) generally incresaes down a column in the periodic table, as long as we compare similar species with simar chargnes
  35. In contrast with protic solvents, __ enhance the __ of anions. An anion is more reactive in an __ because it is __. 

    There are no H bonds to be broken when solvent must make way for the nucleophile to approach an electrophilc carbon atom.
    • aprotic solvents
    • nucleophilicity
    • aprotic solvent
    • not so strongly solvated
  36. The relatively weak solvating ability of aprotic solvents is also a disadvantage. Why?
    most polar, ionic reagents are insoluble in simple aprotic solvents like alkanes
  37. __ have strong dipole moments to enahce solubility, yet they have no O-H or N-H groups to form hydrogen bonds with anions.
    polar aprotic solvents