Orgo 15.12-15.

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DesLee26
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263515
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Orgo 15.12-15.
Updated:
2014-02-23 15:04:19
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CHM 202
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Organic Chemistry
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  1. The DA isa __: Two molecules combine in a one-step, __ to form a new ring. __ such as the DA are one class of __, which involve the concerted forming and breaing of bonds within a closed ring of interacting orbitals.
    • cycloaddition
    • concerted reaction
    • Cycloadditions
    • pericyclic reactions
  2. A __ has a  __, whose Ea may be supplied by heat or UV light. Some __ proceed only under thermal induction, and others proceed only under photochemical induction. Some __ take place under both thermal and photochemical conditions, but the two sets of conditions give different products.
    • concerted pericyclic reaction
    • single TS
    • pericyclic reactions x2
  3. What does the conservation of orbital symmetry say?

    In that case, there will be __ to help stabilizethe TS. Without these bonding interactions int eh TS, the __ is much higher, and the concerted cyclic reaction cannot occur. Conservation of symmetryhas been used to develop "rules" to predict which __ are feasible and what products will result. These rules are often called the __.
    the molecular orbitals of the reactants must flow smoothly into the MOs of the products without any drastic changes in symmetry

    • bonding interactions
    • Ea
    • pericyclic reactions
    • Woodward-Hoffman rules
  4. In the DA reaction, the diene acts as the __ and the dienophile acts as the __.

    The electrons in the highest-energy occupied orbital, called the __ are the most important because they are __. The orbital that receives these electrons is the lowest-energy orbital available, called __. If the electrons can flow smoothly from __ to __, a __ may take place.
    • electron-rich nucleophile
    • electron-poor electrophile
    • Highest Occupied MO (HOMO)
    • Lowest Unoccupied MO (LUMO)
    • HOMO¬†
    • LUMO
  5. Having the correct symmetry means the orbital sthat form the new bonds can __: plus with plus and minus with minus. These bonding interactions stabilize the TS and promote the concerted reaction. This favorable result predicts that the reaction is __. The __ is common, and this theory correctly predicts a favorable TS.
    • overlap constructively
    • symmetry-allowed
    • DA reaction
  6. If a cycloaddition produces an overlap of positive phase orbitals iwth negative phase orbitals, __ are generated, which raise the Ea so the reaction is classified as __.
    • antibonding interactions
    • symmetry-forbidden
  7. When __ rather than heat is used to induce __ our predictions must be reversed.

    When a photon with the correct energy strikes ethylene, one of the pi electrons is excited to the next higher molecular orbital. This higher orbital, formally hte __, is now occupied: It is the new __, the __ of teh excited molecule.
    • UV light
    • pericyclic reactions

    • LUMO
    • HOMO*
    • HOMO
  8. The __ ahs teh same symmetry as the LUMO of a ground-state ethylene. An excited molecule can react with a ground state molecule to give __. The __ is therefore __ bit __.
    • HOMO*
    • cyclobutane
    • [2+2] cycloaddition
    • photochemically allowed but thermally forbidden
  9. In most cases, photochemically allowed reactions are __, and thermally allowed reaections are __
    • thermalyl forbidden
    • photochemically forbidden

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