Chem301 ch6,7,8 USD

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Chem301 ch6,7,8 USD
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Ch6 ch7 ch8 Organic Chem 301 USD chapters parts
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general terms and definitions text book "Organic Chemistry" University of San Diego/ Klein: copyright 2012 John Wiley & Sons, Inc. arrow pushing, carbocations,
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  1. Enthalpy
    • Enthalpy = ∆H = q: Heat of reaction. Enthalpy is used to measure the exchange of energy.
  2. Homolytic Bond Cleavage
    • generates two uncharged species, called radicals, each of which bears an unpaired electron.
  3. Heterolytic Bond Cleavage
    • is illistrated with a two-headed curved arrow, generating charged species, called ions.
  4. Bond Dissociation Energies (Delta Ho) of Common Bonds
    • The amount of energy required to break a covalent bond via homolytic bond cleavage.
  5. Heat of reaction
    The total change in enthalpy (delta Ho) for the reaction.
  6. (+) Delta Ho
    • A positive delta Ho indicates that the system increased in energy (it received energy from the surroundings).
    • Endothermic
  7. (-) Delta Ho
    • A negative delta Ho indicates that the system decreased in energy (it gave energy from the surroundings).
    • Exothermic
  8. Exothermic process
    • The system gives energy to the surroundings (delta Ho is negative).
  9. Endothermic process
    • The system receives energy from the surroundings (delta Ho is positive).
  10. Entropy
    is formally deifined as the measure of disorder associated with a system, although this definition is overly simplistic. Entropy is more accurately described in terms of probabilities (∆S)
  11. Increase in entropy
    • is considered spontaneous.
    • ∆S = (+) = Spontaneous
    • i.e. A—B --> A + B, 1 reactant becomes 2 products.
    • i.e. cyclic becomes acyclic
  12. Delta Ssurr =
  13. Delta Stot =
  14. Delta G
    • Delta G = -RT ln Keq
  15. Delta G for spontaneous reaction
    If delta Stot must be positive in order for a process to be spontaneous, then Delta G must be negative. In order for a process to be spontaneous, delta G for that process must be negative.
  16. Exergonic
    • (-) Delta G = Spontaneous
  17. Endergonic
    • (+) delta G = not spontaneous
  18. Sample values of Delta G and corressponding Keq
  19. Thermodynamics
    The study of how energy is distributed under the influence of entropy.
  20. Kinetics
    • The study of reaction rates.
    • Rate = k [reactants]
    • Rate = k [A]x [B]y
  21. First order
    • Rate = k [A]
    • this is where doubling the concentration of A doubles the effect, but doubling the concentration of B has no effect.
    • [nucleophile concentrations have no effect].
  22. Second order
    • Rate = k [A] [B]
    • In this case, if we were to double either of the concentrations, the rate would also double.
  23. Third order
    • Rate = k [A]x [B]y
    • In this case, doubling the concentration of A will quadruple the reaction rate, while doubling the concentration of B would double the reaction rate.
  24. Energy of activation
    • Ea is the energy barrier (the hump) between reactants and the products.
    • How Temperature effects Ea.
    • Steric hinderance will also effect the Ea.
  25. Catalyst
    • is a compound that can speed up the rate of reaction without being consumed by the reaction. It works by providing an alternative pathway with a smaller activation energy (Ea).
  26. Kinetics (rate of reaction) vs Thermodynamics
    • C +D are thermodynamic products while E+F are the kinetic products.
  27. Transition states
    • A state in which the reaction passes (cannot be isolated). Here is a transition state.
    • The peaks are transition states where as the valleys are intermediates.
  28. Intermediate
    have a certain, albeit short, lifetime. An intermediate is not the breaking or forming of bonds.
  29. Hammond postulate
    • Looking at the graph, if the hump is near the reactants, the reactants than the transition state will look like reactants and will be an EXOTHERMIC process. If the peak is closer to the products then the peak will look more like the products and will be an ENDOTHERMIC process.
  30. Nucleophile
    An electron-rich center. It does the attacking or meaning "nucleus lover". It typically but not always has a negative charge.
  31. Electrophile
    Wants e-, gets attacked by the nucleophile, means electron-deficient, "electron lover".
  32. Carbocation
    a carbon with a positive charge. (C+)
  33. Proton transfers
    A hydrogen moving from one compound to another compound/element.
  34. Rearrangment
    One molecule moving to put (usually a cation) in a different location. Carbocations are the focus in this chapter (6).
  35. Hyperconjunction
    • stabalizes the empty p orbitals. This explains the primary, secondary, and tertiary carbocations.
  36. Allylic carbocation
    a carbocation that stabalizes with RESONANCE.
  37. Alkyl Halide
    A carbon chain with a halide attached. Also called haloalkane or organohalide.
  38. Alpha position
    • The carbon atom connected directly to the halogen.
  39. back-side attack
    • Means that the nucleophile can only attack from the back-side of a compound and after it does, the other three substituents flip to the other side where the leaving group (L.G.) left.
    • 1. The lone pairs of the L.G. creat regions of high e- density that effectivly block the front side of the substrate, so the nucleophile can only attack from the backside.
    • 2. Moleculare Orbital (MO) theory provides a more sophisticated answer. Recall that moleculare associated with the entire molecule (as opposed to atomic orbitals, which are associated with individual atoms). According to MO theory, the e- density flows from the HOMO of the nucleophile into the LUMO of the electrophile. As an example let's focus our attention on the LUMO of the methyl bromide (below). If a nucleophile attacks methyl bromide from the front side, the nucleophile will encounter a node, as a result, no net bonding will result from the overlap between the HOMO of the nucleophile and the LUMO of the electrophile. In contrast, nucleophilic attack from the back side allows for efficient overlap between the HOMO of the nucleophile and the LUMO of the electrophile.
  40. beta position
    • Carbon atoms connected to the alpha position.
  41. biomolecular
    2 chemical entities.
  42. first-order
    • Linearaly dependent on the concentration of only one compound. SN1 Where
    • S: Substitution,
    • N: Nucleophilic.
    • 1: Unimolecular.
  43. haloalkane
    A carbon chain with a halide attached. Also called alkyl halide or organohalide.
  44. inversion of configuration
    Means that the nucleophile can only attack from the back-side of a compound and after it does, the other three substituents flip to the other side where the leaving group (L.G.) left.
  45. leaving group
    denoted by (L.G.) a group capable of seperating from the substrate.
  46. organohalide
    A carbon chain with a halide attached. Also called alkyl halide or haloalkane.
  47. polar aprotic solvent
    • Contain no hydrogen atoms connected directly to an electronegative atom. Use with SN2.
  48. polar protic solvent
    Contain at least one hydrogen atom connected directly to an electronegative atom. Use with SN1.
  49. Primary alkyl halide
    • The carbon that is attached to the halide is also attached to one other Carbon, (reference Carbon).
  50. rate-determining step
    (RDS) The slow step is called the rate-determining step because it is the fastest step, or the lowest Ea.
  51. retention of configuration
    • Replaced the L.G. (same spot),
  52. secondary alkyl halide
    • The carbon that is attached to the halide is also attached to two other Carbons, (reference Carbon).
  53. SN1
    • S: Substitution
    • N: Nucleophilic
    • 1: Unimolecular
    • Use polar protic solvent.
    • Substrate:       Tertiary
    • Nucleophile:  Weak nucleophile
    • L.G.:              Excellent leaving group
    • Solvent:          Polar protic
  54. SN2
    • S: Substitution
    • N: Nucleophilic
    • 2: bimolecular: the step involves 2 chemical entities.
    • Use polar aprotic solvent.
    • Substrate:       Methyl or primary
    • Nucleophile:  Strong nucleophile
    • L.G.:              Good leaving group
    • Solvent:          Polar Aprotic
    • Reactivity diagrame
  55. solvolysis
    Any time the attacking nucleophile is neutral, a proton transfer is necessary at the end of the mechanism.
  56. stereospecific
    Aconfiguration of the product is dependent on the configuration of the starting material.
  57. substitution reaction
    involves the exchange of one functional group or another.
  58. substrate
    The electrophile in a substitution reaction.
  59. sulfonate ions
    • The best L.G. is triflate, most commonly used is tosylate.
  60. tertiary alkyl halide
    • The carbon that is attached to the halide is also attached to three other Carbons, (reference Carbon).
  61. tosylate
    • Most commonly used sulfonate ion.
  62. unimolecular
    One chemical entity.
  63. Possable mechanisms for substitution reactions
    • 1. Nucleophilic attack
    • 2. Loss of leaving group (L.G.)
    • 3. Proton transfer
    • 4. Carbocation (C+) Rearrangment.
  64. Common nucleophiles
  65. Factors that favor SN1 and SN2 process
  66. 1,2-elimination
    Also called beta-elimination. Where a proton p+ from the beta position is removed together with the leaving group (L.G.). This can be accomplished with any good leaving group.
  67. alkenes
    Double bonded carbon atoms (C=C).
  68. anti-coplanar
    • Where after a double bond forms and there is a "E" formation.
    • ________
  69. anti-periplanar
    • If two bonds define two line segments, then they are anti-periplanar if they are anti-parallel in the plane they define. It's much easier to see anti-periplanar bonds than it is to explain them. In the following diagram, the C-H and C-LG bonds are anti-periplanar:
  70. beta elimination
    Also called 1,2-elimination. Where a proton p+ from the beta position is removed together with the leaving group (L.G.). This can be accomplished with any good leaving group.
  71. Bredt's rule
    • It is not possable for a bridgehead carbon of a bicyclic system to prosess a C=C double bond if it involves a trans pie bond being incorperated in a small ring.
    • ie:
  72. coplanar
    • All lieing in the same plane.
    • With the Br and H leaving, a pie bond will form between the carbons. Recall that a pie bond is the overlapping of p orbitals. therefore a transition state must involve the formation of p orbitals that are positioned such that they can overlap with each other as they are forming. In order to achieve this kind of orbital overlap, the following four atoms must all lie in the same plane: the proton p+ at the Beta position, the leaving group (L.G.), and the two carbon atoms that will ultimately bear the pie bond.
  73. degree of substitution
    • Using the parent chain as reference carbons.
  74. dehydration
    When the leaving group is water. or The removal of water.
  75. dehydrohalogenation
    • The leaving group is hydrogen and a halogen ie.
    • HF, HCl, HBr, HI
  76. E
    • Refering to the main priorities located on the oppisite ends of a double bond are going in the opposite direction.
    • ie:
  77. E1
    • E: elimination, 1: unimoleculare
    • Rate = k [substrate]
    • Much like the SN1 reaction, the rate is linearly dependent on the concentration of only one compound (the substrate). This observation is consistent with the stepwise mechanism (loss of the leaving group), just as we saw in SN1 reaction. The base does not participate in this step, and therefore, the concentration does not affect the rate.
  78. E2
    • E: elimination, 2: bimoleculare
    • Rate = k [substrate] [base]
    • Tertiary substrates react readily in E2 reactions: in fact, they react even more rapidly then primary substrates.
    • Much like the SN2 reaction, the rate is linearly dependent on the concentrations of two different compounds (the substrate and the base). The observation suggests that the mechanism must exhibit a step in which the substrate and the nucleophile collide with each other. This is consistant with a conserted mechanism in which there is only one mechanistic step involving both the substrate and the base.
  79. Hofmann product
    • = the minority in a regioselective reaction.
    • These are important because if we switch out the base with a larger sterically hindered base, we will cause a shift in the products to have the majority shoft to the Hofmann instead of Zaitsev.
    • Examples of large commonly used bases:
  80. periplanar
    Used to describe a situation in which the proton p+ and leaving group are nearly coplanar (for example, a dihedral angle of 178o or 179o). In such a conformation, the orbital overlap is significant enough for an E2 reaction to occur. Therefore, it is not absolutely necessary for the proton (p+) and the leaving group to be anti-coplanar. Rather it is sufficient for the proton (p+) and the leaving group to be anti-periplanar.
  81. regiochemistry
    • When the beta position "H" can be removed from other adjacent atoms and will cause a different product.
    • Typically there are major and minor catagories associated to it, not always.
  82. regioselective
    When there is an option for the beta position to come from different adjacent atoms.
  83. stereoselective
    "stereo"-"selective". Substrates produce two stereoisomers in unequal amunts.
  84. stereospecific
    • The stereoisomerism of the product is dependent on the stereoisomerism of the substrate. The stereospecificity of an E2 reaction is only relavent when the beta position has only one proton:
  85. syn-coplanar
    • Where after a double bond forms and there is a "Z" formation.
    • ________
  86. Z
    • ZameZide; meaning that the main priorities located on the oppisite ends of a double bond are going in the same direction.
    • ie: 
  87. Zaitsev product
    = the majority in a regioselective reaction.
  88. t-BuOK
    • Sterically hindered base used to get Hofmann from Zaitsev.
  89. Diisopropylamine
    • Sterically hindered base used to get Hofmann from Zaitsev.
  90. Triethylamine
    • Sterically hindered base used to get Hofmann from Zaitsev.
  91. Concerted process
    a base abstracts a proton and the leaving group leaves simultaneously.
  92. Stepwise process
    first the leaving group leaves, and then the base abstracts a proton.
  93. Nucleophiles (only)
  94. Base (only)
  95. Strong Nuc  /  Strong Base
  96. Weak Nuc  /  Weak Base

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