Concept explainers
The energy-level diagram in Figure 9.36 shows that the sideways overlap of a pair of p
orbitals produces two molecular orbitals, one bonding and one antbonding. In ethylene there is a
pair of electrons in the bonding n orbital between the two carbons. Absorption of a photon of the
appropriate wavelength can result in promotion Of one Of the bonding electrons from the r2p to the
Ir. molecular orbital.
a. Assuming this electronic transition corresponds to the HOMO-LUMO transition, what is the
HOMO in ethylene?
b Assuming this electronic transition corresponds to the HOMO-LUMO transition, what is the
LUMO in ethylene?
c. Is the bond in ethylene stronger or weaker in the excited State than the ground state?
d. Is the C-C bond in ethylene easier to twist in the ground state or in the excited state?
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Chemistry: The Central Science (14th Edition)
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