Orgo Ch 4.15- 4.

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Orgo Ch 4.15- 4.
2013-10-02 06:40:52
CHM 201

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  1. What do we want to prevent or redard?
    free radical reactions
  2. __ may decompose or polymerize by __. Even the cells in living systems are damaged by __, wihich can lead to aging, cancerous mutations, or cell death.
    • chemical intermediates
    • free-radical chain reactions
    • radical reactions
  3. __ are often added to foods and chemicals to retard spoilage by radical chain reactions. CHain reactions depend on what?
    • radical inhibitors
    • the individual steps beign fast, so that each initiation step results in many molecules reactions
  4. How can an inhibitor stop a chain?
    reacting witha radical intermediate in fast, highly exothermic step to form an intermediate that is relatively stable. The next step in the chain becomes endothermic and very slow
  5. Radical inhibitors also helpt to protect the __.
    cells of lviing systems.
  6. Like BHA, which is added to foods as an antioxidant to stop __ by reacting with radical intermediates for form a relatively stable __, vitamin E is a __ and is thought to react with radicals by losing the __ hydrogen atom.
    • oxidation
    • free-radical intermediate
    • phenol
    • OH
  7. __ are short lived species that are never present in high concentrations because they react as quikcly as they are formed
    reaction intermediates
  8. In most cases, __ are fragments of molecules (lie free radicals), often having atoms with unusual number s of bonds. Some of hte common __ contain carbon atoms with only two or three bonds, compared with C's four bonds in stable compounds. Such species react quickly with a variety of compounsd to give more stable products with __.
    • reaction intermediates x2
    • tetravalent C atoms
  9. Although __ are nto stable compounds, tehy are important to our study of orgo. Most __ involve __.
    • reactive intermediates
    • reaction mechanisms
    • reactive intermediates
  10. Species with __ are classified according to their __, which depends on the number of __.
    • trivalent carbon
    • charge
    • nonbonding electrons
  11. The __ have no nonbonding electrons and are positively charged. The __ have one nonbonding electron and are neutral. The __ have a pair of nonbonding electrons and are negatively charged.
    • carbocations
    • radicals
    • carbanions
  12. The most common intermediates with a __ are the __, which has two nonbonding electrons on the divalent carbon atom, making it uncharged.
    • divalent carbon atom
    • carbenes
  13. A __ is a species that contains a carbon atom bearing a positive charge. The positively charged carbon atom is bonded to three other atoms, and it has no __, so it has only __ electrons in  its valence shell. It is __, with a __ and bond angles of about __.
    • carbocation (carbonium ion/ carbenium ion)
    • nonbonding electrons
    • six
    • sp2 hybridized
    • planar structure
    • 120
  14. With only six electrons in the positive carbon's valence shell, a __ is a powerful __ and it may react with any __ it encounters. Like other strong acids, __ are unlikely to be found in basic solutions. __ are proposed as __ in many types of organic reactions.
    • carbocation
    • electrophile
    • nucleophile
    • carbocations
    • carbocations
    • intermediates
  15. Like free radicals, carbocations are __ species: They have fewer than eight electrons in the valence shell.
    electron deficient
  16. Also, like free radicals, carbocations are stabilized by __. Any __ stabilizes an electron-deficient carbocation in two ways. What are they?
    • alkyl substituents
    • 1) inductive effect
    • 2) partial overlap of filled orbitals with empty ones
  17. This __ is a donation of electron density through the __ of the molecule. The positively charged carbon atom withdraws some __ from the __ bonded to it.
    • inductive effect
    • sigma bonds
    • electron density
    • polarizable alkyl groups
  18. __ also have filled __ that can overlap with the empty p orbital on the positively charged carbon atom, further stabilizing teh __. Even though the attached __ rotates, one of its __ is always aligned with the empty p orbital, stabilizing teh __ carbon atom. This type of overlap between a p orbital and a sigma bond is called __.
    • alkyl substituents
    • sp3 orbitals
    • carbocation
    • alkyl group
    • sigma bonds
    • electron-deficieint
    • hyperconjugation
  19. In general, more highly substituted carboocations are what?
    more stable
  20. Unsaturated carbocations are also stabilized by __. if a pi bond is adjacent to a carbocation, what will happen?
    • resonance stabilization
    • the filled p orbitals of the pi bond will overlap with the empty p orbital of the carbocation
  21. What is the result?
    __ is particulraly effective in stabilizing carbocations.
    • delocalized ion, with the positive charge shared by two atoms
    • resonance delocalization
  22. Carbocations are common __ in organic reactions. Highly substituted __ can ionize when they are heated in a polar solvent. The strongly __ reacts wtih any available __, often the solvent.
    • intermediates¬†
    • alkyl halides
    • electrophilic carbocation¬†
    • nucleophile
  23. Carbocations are also strong __.
    strong proton acids
  24. Like carbocations, free radicals are __ and __. Unlike carbocations, however, the p orbital perpendicular to the plane of the CH bonds of the radical is not __; it contains __.
    • sp2 hybridized
    • planar (or nearly planar)
    • empty
    • the odd electron
  25. Both radicals and carbocations are __ because they __ around the carbon atom. Like carbocations, radicals are stabilized by the electron-donating effect of __, making more highly substituted radicals more stable.
    • electron deficient
    • lack an octet
    • alkyl groups
  26. LEss energy is required to break a __ bond to form a more __.
    • CH
    • highly substituted radical
  27. Like carbocations, radicals can be stabilzized by __. Overlap with the p orbitals of a pi bond allows the __ to be __ over two carbon atoms. __ is particularly effective in stabilizing a radical.
    • resonance
    • odd electron
    • delocalized
    • resonance delocalization
  28. A carbanion has a __ that bears a - charge. There are eight electrions around the carbon atom (three bonds and one lone pair), so it is not __; rather, it is __ and a strong __. A carbanion has the same electronic structure as an __.
    • trivalent carbon atom
    • electron deficient
    • electron rich
    • strong nucleophile (Lewis base)
    • amine
  29. The hybridization and bond angles of a simple carbanion also resemble those of an __. The carbon atom is __ and __. One fo the __ is occupied by an __.
    • amine
    • sp3 hybridized
    • tetrahedral
    • tetrahedral positions
    • unshared lone pair of electrons
  30. Like __, carbanions are __ and __. A carbanion has a negatve charge on its carbon atom, however, making it a powerful __ and a stronger __ than an __>
    • amines
    • nucleophilic
    • basic
    • base
    • nucleophile
    • amines
  31. Like other strong bases, carbanions are unlikely to be found in __. The stability order of carbanions reflects their __. __ and other __ slightly destabilize a carbanion. The order of stability is usually what?
    • acidic solutions
    • high electron density
    • alkyl groups
    • electron-donating groups
    • the opposite of that for carbocations and free radicals
  32. Carbanions that occur as __ in organic reactions are almost always stabilized by neightboring groups. They can be stabilized by either __ or __.
    • intermediates
    • inductive effect
    • resonance
  33. __ also plays a role in stabilizing carbanions.
  34. __ are the most common type of carbanions we will encounter in orgo rxs.
    resonance-stabilized carbanions
  35. __ are uncharged reactive intermediates containing a __.
    • carbenes
    • divalent carbon atom
  36. The simplest has the formula __ and is called __, just as a -CH2-- group in a molecule is a __.
    • :CH2
    • methylene
    • methylene group
  37. One way of generating carbenes is to what?
    form a carbanion that can expel a halide ion
  38. A carbene has both a __ and an __, so it can react as a __ or as an __.
    • lone pair of electrons
    • empty p orbital
    • nucleophile electrophile
  39. The most common sythetic reaction of carbenes is their __.
    addition to double bonds to form cyclopropane rings
  40. No simple carbenes have ever been purified or even made in a hiigh concentration. Why?
    because when two carbenes collide, they immediately dimerize to give an alkane (dimerize= two bond together)
  41. __ and __ are useful both the __ of other compounds and for investigation of __. The __ is generated in the presence of its target compound, so that it can react immediately, and the concentration of the carbene is always low.
    • carbenes
    • carenoids (carbene-like reagents)
    • synthesis
    • reaction mechanisms
    • carbene intermediate