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Chapter 8 261
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conjugated double bonds
double bonds separated by one single bond.
contributing resonance
a structure with localized electrons that approximates the true structure of a
structure
compound with delocalized electrons.
cumulated double bonds
double bonds that are adjacent to one another.
cycloaddition reaction
a reaction in which two
p
electron-containing reactants combine to form a single
cyclic product.
3
4 2
4
cycloaddition
a cycloaddition reaction in which six
p
electrons participate in the transition state
reaction
with four
p
electrons coming from one reactant and two
p
electrons coming from
the other reactant.
delocalization energy
the extra stability associated with a compound as a result of having delocalized
(resonance energy)
electrons.
delocalized electrons
electrons that result from a
p
orbital overlapping the
p
orbitals of two adjacent
atoms; therefore, delocalized electrons are shared by three or more atoms.
Diels–Alder reaction
a
3
4
+
2
4
cycloaddition reaction.
diene
a hydrocarbon with two double bonds.
dienophile
an alkene that reacts with a diene in a Diels–Alder reaction.
direct addition
addition to the 1- and 2-positions of a conjugated system.
(1,2-addition)
donation of electrons by
donation of electrons through
p
bonds.
resonance
electron delocalization
the sharing of electrons by more than two atoms.
endo
a substituent is endo if it and the bridge are on opposite sides of a bicyclic
compound.
equilibrium control
thermodynamic control.
exo
a substituent is exo if it and the bridge are on the same side of a bicyclic compound.
fused rings
rings that share two adjacent carbons.
highest occupied
the highest-energy molecular orbital that contains electrons.
molecular orbital (HOMO)
heteroatom
an atom other than carbon.
heterocyclic compound
a cyclic compound in which one or more of the atoms of the ring is a heteroatom.
(heterocycle)