Fin05 Ans - Some answers to the Chemistry 301-301A Final...

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Some answers to the Chemistry 301-301A Final Examination, January 12, 2005 1. O CH 3 H 3 C H 3 O + H 2 O O CH 3 H 3 C H 2 O O CH 3 H 3 C O H H CH 3 OH CH 3 O H H H 2 O CH 3 O H H CH 3 O H H OH 2 H OH 2 O CH 3 H 3 C O H H H 3 O + O CH 3 H 3 C O H O H 3 C H 2 O + + + + + + + IR: 1725, 2850, 2750 cm –1
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2. . HC CH 2 CH 2 HC CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 3 4 5 (a) (b) Bonds broken = 3 pi bonds = 3 x 66 = 198 kcal/mol Bonds made = 1 pi bond and 2 sigma bonds = 66 + 2 x 85 = 236 kcal/mol so this reaction is exothermic by 236 – 198 = 38 kcal/mol Bonds broken = 2 pi bonds = 2 x 66 = 132 kcal/mol Bonds made = 2 sigma bonds = 2 x 85 - 90 = 170 - 180 kcal/mol so this reaction is also exothermic, again by 170-132 = about 38 kcal/mol In fact we should correct this value for the ca. 20 - 25 kcal strain in cyclobutane, which brings the number down to about 20 kcal/mol. If you knew this fine, if not, now you do.
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Here are the MOs for all the species involved in reaction (a): HC CH 2 CH 2 HC CH 2 CH 2 HOMO butadiene LUMO butadiene LUMO ethene HOMO ethene Notice that both HOMO-LUMO interactions allow both the new sigma bonds to be formed in cyclohexene. HOMO (ethene) LUMO (butadiene) is shown below, but HOMO(butadiene) LUMO(ethene) also works. By contrast, the HOMO-LUMO interaction for the combination of two ethenes leaves one bond of cyclobutane unmade. So, even though the combining of two ethenes into one cyclobutane is
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This note was uploaded on 03/07/2010 for the course ORGO 1 AND V.0243 taught by Professor Jones during the Spring '10 term at NYU.

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Fin05 Ans - Some answers to the Chemistry 301-301A Final...

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