Ch21 - 5 10 S olutions Chapter 20 Conjugated Systems...

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510 Solutions Chapter 20: Conjugated Systems (b) Explain the position of equilibrium. Conjugation is stabilizing, so the conjugated 2-cyclohexenone is favored at equilibrium compared to 3- . cyclohexenone, which is not conjugated. . Orangefin anemonefish Ainphiprion chrysoptet:tJ,s in a StichodactyJa kenti anenome Bora Bora, French Polynesia ~,""' .... ;, -.~ . , .~. Reticulated buttert1yfish Chaetodo~ reticulatus Bora Bora; French Polynesia Chapier 21: Benzene and the Concept of Aromaliciry Solutions. 51l CHAPTER 21 SolutWns to the Problems Problem 2 1 .1 Construct a Frost circle for a planar eight-membered ring with one 2p orbital on each atom of the ring, and show the relative energies of its eight n molecular orbitals. Which are bonding MOs, which are antibonding, and which are nonbonding? :1t8 • Antibonding . -------- -------- :1t 4 Nonbonding -------- '---'-~-~---____jt_--' eight uncombined2p orbitals Bonding I Problem 2·1.2 Which compound gives a signal in the IH-NMR spectrum with a larger chemical shift, furan or cyclopentadiene? Explain. o . . o Furan Cyclopentadiene Furan is aromatic by virtue of a lone pair on the oxygen atom, when combined with the four 1t electrons of the carbon-carbon double bonds give six 1t electrons. Being aromatic, the hydrogens on this aromatic ring are deshielded by the induced ring current and appear farther downfield compared to those of the nonaromatic cyclopentadiene. Problem 21.3 Describe the ground-state electron configuration of the cyclopentadienyl cation and radicaL Assuming each species is planar,would you expect it to be aromatic or antjarom~tic? Cyclop.entadienyl cation: 1t4* - -4- + +- -~--------- five uncombined 2p orbitals, with four electrons ground state electron configuration of the cyclopentadienyl cation
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512 Solutions Chapter 21: Benzene and the Concept of Aromaticity Chapter 21: Benzene and the Concept of Aromaticity Solutions 513 Cyclopentadienyl radical: 4- 4- ++ -4- ----------- five uncombined 2p orbitals, with five electrons ground state electron configuration of the cyclopentadienyl anion The cyclopentadienyl cation has 4 It electrons so it is antiaromatic. The cyclopentadienyl radical has five electrons, so it is neither aromatic (4n + 2) nor antiaromatic (4n). PrQblem t I.~ Describe the ground-state ~lectrQn cQnfi~uratiQn Qf the cyciQheptatrienyl radical and aniQn. Assuming that each species tS planar, WQuid YQU expect It tQ be arQmatIc or antiarQmatic? Cycloheptatrienyl radical: -t- 4- + + ----~~~-~- seven uncombined 2p orbitals; with seven electrons· ground state electron configuration of the cycloheptatrienyl radical Cycloheptatrienyl anion: It 5 * 4t 4- 4- 4- + + +----~~~--- seven imcombined2p orbitals, with eight electrons ground state ~lectron configuration of the cycloheptatrienyl anion The cycloheptatrienyl anion has 8 electrons so it is antiaromatic. The cycloheptatrienyl radical has seven electrons, so it is neither aromatic·(4n + 2) or antiaromatic (4n).
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This note was uploaded on 07/09/2011 for the course CHE 301 taught by Professor Diver during the Spring '08 term at SUNY Buffalo.

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Ch21 - 5 10 S olutions Chapter 20 Conjugated Systems...

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