Organic Chemistry chp. 15 terms

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Organic Chemistry chp. 15 terms
2011-09-15 11:01:26
organic chemistry Wade Jr

Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
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  1. 1,2-addition
    addition in which two atoms or groups add to adjacent atoms
  2. 1,4-addition
    addition in which two atoms or groups add to atoms that have a 1,4-relationship
  3. allyl group
    common name for the 2-propenyl group, -CH2-CH2-=CH2-
  4. allylic position
    carbon atom next to a C=C bond, eg. allylic cation, allylic radical, allylic anion
  5. allylic shift
    isomerization of a double bond occuring through delocalization of an allylic intermediate
  6. concerted reaction
    reaction in which all bond making and braking occurs in the same step, eg. E2, SN2, Diels-Alder
  7. conjugated double bonds
    double bonds alternating with single bonds, interaction by p orbitals overlaping in the pi bonds
  8. isolated double bonds
    double bonds separated by two or more single bonds, react like a simple alkene
  9. cumulated double bonds
    successive double bonds with no single bonds in between
  10. allene (cumulen)
    compound containing cumulated C=C bonds
  11. conservation of orbital symmetry
    pericyclic reaction theory in which the MOs of the reactants flow directly into the MOs of the products with out significant changes in symmetry, bonding interactions stabilize the transition state
  12. constructive overlap
    overlap of orbitals that contributes to bonding, generally overlap of lobes with similar phases, eg. + with + or - with -
  13. cycloaddition
    reaction of two alkenes or polyenes to form a cyclic product, often through concerted interactions of pi e- in two unsaturated molecules
  14. delocalized orbital
    molecular orbital resulting from the combination of three or more atomic orbitals, when filled orbitals spread e- density over all the atoms
  15. descructive overlap
    overlap of orbitals contributing to antibonding, generally overlap of lobes with opposite phases, eg + with -
  16. Diels -Alder reaction
    synthesis of six membered ring by [4 + 2] cycloaddition, four pi e-’s in one molecule interact with 2 pi e-’s in the other molecule to form a new ring
  17. dieneophile
    component with 2 pi e-’s interacts with diene in Diels-Alder reaction
  18. endo rule
    stereochemical preference for electron-poor substituents in the dienophole endo positions of a bicyclic Diels-Alder product
  19. secondary overlap
    overlap of p orbital e- withdrawing groups of the dieneophile with one of the central atoms of the diene, helps stabilize transition state, favors endo products in cyclic dienes
  20. heat of hydrogenation
    enthalpy of reaction accompanying addition of hydrogen to a mole of an unsaturated compound
  21. HOMO
    highest occupied molecular orbital, in a photochemically excited state this orbital is represented as HOMO*
  22. kinetic control
    product distribution governed by rates at which products form
  23. kinetic product
    product that is formed fastest, the major product under kinetic control
  24. LUMO
    lowest unoccupied molecular orbital
  25. molar absorptivity (molar extinction coefficient)
    measure of how strongly a compound absorbs light at a particular wavelength, Beers law A = log (Ir /Is) = Ecl, A is the absorbance, Ir and Is are the amount of light passing through the reference and the sample, c is the sample concentration in moles per liter, l is the length of light passing through the cell
  26. molecular orbitals (MO’s)
    orbitals that contain more than one atom in the molecule, can be bonding, antibonding or nonbonding
  27. bonding molecular orbitals
    MO’s lower in energy than individual MO’s from which they were made, e-’s in these orbitals hold the atoms together
  28. antibonding molecular orbitals
    MO’s higher in energy than the individual MO’s from which they were made, e-’s in these orbitals push atoms apart
  29. nonbonding molecular orbitals
    MO’s with the same energy as the individual MO’s from which they were made, e- in these orbitals have no effect on the atoms
  30. node
    a region of molecular orbital with zero e- density
  31. pericyclic reaction
    reaction involving concerted reorganization of e-’s in a closed loop of interacting orbitals, one class are cycloadditions
  32. reference beam
    a second beam passes through the reference cell containing only the solvent, the sample beam is compared to this beam to compensate for absorption by the cell or the solvent
  33. resonance energy
    extra stabilization by delocalization compared to a localized structure, in dienes and polyenes resonance energy is extra stability of the conjugated system compared to a compound with and equivelent number of independent bonds
  34. s-cis conformation
    cis-like conformation of a single bond in a conjugated diene or polyene
  35. s-trans conformation
    trans-like conformation of a single bond in a conjugated diene or polyene
  36. symmetry-allowed
    MO’s of the reactants may flow into the MO’s of the products in one concerted step according to rules of conservation of orbital symmetry, in symmetry-allowed cycloaddition there is constructive overlap between the HUMO of one molecule with the LUMO of the other
  37. symmetry-forbidden
    MO’s of the reactants are of incorrect symmetries to flow into those of the products in one concerted step
  38. thermodynamic control (equilibrium control)
    product distribution is governed by stability of the products, operates when the reaction is allowed to come to equilibrium
  39. thermodynamic product
    most stable product, major product under thermodynamic control
  40. UV-visable spectroscopy
    measurement of the absorption of ultraviolet and visible light as a function of wavelength, UV wavelength 100-400nm, visible wavelength 400-750nm
  41. Woodward-Fieser rules
    rules that correlate values of ?max in the UV-visable spectrum with structures of conjugated systems
  42. Woodward-Hoffman rules
    symmetry rules that predict whether a pericyclic reaction is symmetry-allowed or symmetry-forbidden