Concept explainers
(a)
Interpretation:
MO energy diagram of twisted ethane is to be drawn and the HOMO and LUMO identified.
Concept introduction:
The molecular orbital energy diagram of a molecule is built by considering the interactions of all the valence shell orbitals from each atom. The total number of MOs produced is the same as the number of interacting AOs.
An end-on overlap of two orbitals produces a pair of MOs of
Interactions between p orbitals produce MOs of two types, one pair with
The valence electrons of the contributing atoms are then filled in these MOs in increasing order of energy. The MO of highest energy that contains any electrons is called the highest occupied molecular orbital (HOMO), and the empty MO immediately above it is called the lowest unoccupied molecular orbital (LUMO).
(b)
Interpretation:
Why the all planar ethane molecule is more stable than the twisted one is to be explained by comparing the MO energy diagrams of the two.
Concept introduction:
Bonding MOs have lower energy than the contributing AOs; nonbonding MOs are essentially at the same level as the AOs, while the antibonding MOs have higher energy compared to the AOs. Therefore, the presence of electrons in bonding MOs stabilizes the molecule compared to the individual atoms. Electrons in nonbonding MOs have no effect. Any electrons in antibonding MOs destabilize the molecule.
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Chapter 3 Solutions
Organic Chemistry: Principles and Mechanisms (Second Edition)
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- Answer the following questions for 1,3,5- hexatriene, the conjugated triene containing six carbons. Which MOs are the frontier molecular orbitals?arrow_forwardMeasure the C-C-C and C-C-H bond angles in the energy-minimized models of cis and trans isomers of cyclooctene. Compare these values with those predicted by VSEPR. In which isomer are deviations from VSEPR predictions greater?arrow_forwardHow would you develop a molecular orbital for a structure like buta-2-diene that has an anion on the first carbon and a cation on the fourth carbon? Also, how would MO look like for 2-dimethyl-1,3-pentadiene?arrow_forward
- The potential energy of a CH3 group in ethane as it is rotated around the C-C bond can be written V= 1/2V0(1 +cos φ), where φ is the azimuthal angle as shown and V0 = 11.6 kJ mol-1. (a) What is the change in potential energy between the trans and fully eclipsed conformations? (b) Show that for smal lvariations in angle, the torsional (twisting) motion around the C-C bond can be expected to be that of a harmonic oscillator. (d) Estimate the vibrational frequency of this torsional oscil lation.arrow_forward8. How many total electrons reside in MOs of symmetry in the following molecule?arrow_forwardDoes chloromethane contain a plane of symmetry? Is it a chiral?arrow_forward
- Explain why the following molecule prefers to adopt an axial conformation for the methyl group.arrow_forwardBuild the molecular models of cis-1,2-dichlorocyclopentane and trans-1,2-dichlorocyclopentane. Then draw the three-dimensional structuresarrow_forwardDraw one all-bonding MO, thena pair of degenerate MOs, and then a final pair of degenerate MOs. Draw the energydiagram, fill in the electrons, and confirm the electronic configurations of the cyclopentadienyl cation and anionarrow_forward
- Organic Chemistry: A Guided InquiryChemistryISBN:9780618974122Author:Andrei StraumanisPublisher:Cengage Learning