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Copyright © 2017 Pearson Education, Inc.
CHAPTER 28
Pericyclic Reactions
Important Terms
antarafacial bond
formation and/or cleavage of two
s
bonds that occur on opposite sides of the
p
formation
system of the reactant.
antarafacial
a rearrangement where the migrating group moves to the opposite face of the
p
rearrangement
system.
antibonding
P
molecular
a molecular orbital that results when two parallel atomic orbitals with opposite
orbital
phases interact. Electrons in an antibonding orbital decrease bond strength.
antisymmetric molecular
a molecular orbital in which the left half is not a mirror image of the right half
orbital
but would be if one-half of the MO were turned upside down.
bonding
P
molecular
a molecular orbital that results when two parallel atomic orbitals with the
orbital
same phase interact. Electrons in a bonding orbital increase bond strength.
Claisen rearrangement
a [3,3] sigmatropic rearrangement of an allyl vinyl ether.
conrotatory ring closure
a ring closure that achieves head-to-head overlap of
p
orbitals by rotating the
orbitals in the same direction.
conservation of orbital
a theory that explains the relationship between the structure and stereochemistry of
symmetry theory
the reactant, the conditions under which a pericyclic reaction takes place, and the
stereochemistry of the product.
Cope rearrangement
a [3,3] sigmatropic rearrangement of a 1,5-diene.
cycloaddition reaction
a reaction in which two
p
-bond-containing molecules react to form a cyclic
compound.
disrotatory ring closure
a ring closure that achieves head-to-head overlap of
p
orbitals by rotating the
orbitals in opposite directions.
electrocyclic reaction
an intramolecular reaction in which a new
s
bond is formed between the ends of a
conjugated system.
excited state
a description of which orbitals the electrons of an atom or a molecule occupy when
an electron in the ground state has been moved to a higher-energy orbital.
frontier orbital analysis
an analysis that determines the outcome of a pericyclic reaction using frontier
orbitals.
frontier orbitals
the HOMO and the LUMO of the two reacting species in a pericyclic reaction.
frontier orbital theory
a theory that, like the conservation of orbital symmetry, explains the relationship
between reactant, product, and reaction conditions in a pericyclic reaction.