MO's for Cyclobutadiene all antibonding node node antibonding bonding bonding antibonding bonding antibonding node π3 all bonding Copyright2005 Pearson Prentice Hall,Inc. 11
Chapter 16 11 MO’s for Cyclobutadiene =>
Energy Diagram for Cyclobutadiene ·Following Hund's rule,two electrons are in separate nonbonding 不3 orbitals. line ·This diradical would be very reactive. TI- Copyright2005 Pearson Prentice Hall,Inc => Chapter 16 12
Chapter 16 12 Energy Diagram for Cyclobutadiene • Following Hund’s rule, two electrons are in separate orbitals. • This diradical would be very reactive. =>
Polygon Rule The energy diagram for an annulene has the same shape as the cyclic compound with one vertex at the bottom. nonbonding line benzene cyclobutadiene cyclooctatetraene Copyright 2005 Pearson Prentice Hall,Inc. => Chapter 16 13
Chapter 16 13 Polygon Rule The energy diagram for an annulene has the same shape as the cyclic compound with one vertex at the bottom. =>
Aromatic Requirements Structure must be cyclic with conjugated pi bonds. Each atom in the ring must have an unhybridized p orbital. The p orbitals must overlap continuously around the ring.(Usually planar structure.) 。 Compound is more stable than its open- chain counterpart. Chapter 16 14
Chapter 16 14 Aromatic Requirements • Structure must be cyclic with conjugated pi bonds. • Each atom in the ring must have an unhybridized p orbital. • The p orbitals must overlap continuously around the ring. (Usually planar structure.) • Compound is more stable than its openchain counterpart. =>
Anti-and Nonaromatic Antiaromatic compounds are cyclic, conjugated,with overlapping p orbitals around the ring,but the energy of the compound is greater than its open-chain counterpart. Nonaromatic compounds do not have a continuous ring of overlapping p orbitals and may be nonplanar. 二> Chapter 16 15
Chapter 16 15 Anti- and Nonaromatic • Antiaromatic compounds are cyclic, conjugated, with overlapping p orbitals around the ring, but the energy of the compound is greater than its open-chain counterpart. • Nonaromatic compounds do not have a continuous ring of overlapping p orbitals and may be nonplanar. =>