10-06 - 10/6/2010 Which reactant is acting as the base in...

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Unformatted text preview: 10/6/2010 Which reactant is acting as the base in the following transformation. Molecule Makers CHEMISTRY Richard F. Heck, Ei-ichi Negishi and Akira Suzuki share the 2010 Nobel Prize in Chemistry for developing new, more efficient ways of linking carbon atoms together to build the complex molecules that are improving our everyday lives. Which reactant is acting as the base in the following transformation. A B A B Knowing that the puckered form of cyclobutane is more stable which of the following cyclobutanes would you predict to be more stable? Structural studies have shown that cyclobutane has a puckered rather than a planar conformation. more stable puckered conformation of cyclobutane more stable puckered conformation of cyclobutane Which of the following factors contribute to the greater stability of the puckered conformation for cyclobutane? 1. The puckered conformation has less angle strain. 2. The puckered conformation has less torsional strain. A. only 1 B. only 2 C. both 1 and 2 A B What are the shapes of these cycloalkanes? H H H H H C C H H C C H H H H H H H C C H C H H C C H H H H H H H C C H C H C C H H The methylenes in these compounds have different stabilities. H H H H H H C H C C H H H H H H C C H H C C H H H H H H H C C H C H H C C H H H H H H H H C C H C H C C H H H H H H C H H C H C C C cyclopropane planar actual 60° 60° cyclobutane 90° 88° cyclopentane 108° 105° cyclohexane 120° 109.5° How could the relative stabilities of the methylenes in these cycloalkanes be determined? A. Record their infrared spectra. B. Measure their heats of combustion. C. Determine their boiling points. D. Determine their solubility in water. E. Measure their color. Would cyclopentane be predicted to be A. planar or B. puckered? 1 10/6/2010 Which of these cycloalkanes is the most stable? H C H H C C H H H H H H C C H H C C H O2 CO2 + H2O + heat H H H H H H C C H C H H C C H O2 CO2 + H2O + heat H H H H H H H C C H C H C C H O2 CO2 + H2O + heat H H H H Why is more heat released when cyclopropane is burned? H C H H C C H H H H H C C H H C C H H H H H H C C H H C H H C C H H H H H H H H C C H C H C C H H H C heats of combustion O2 CO2 + H2O + heat H H H 697 O2 ΔHº/CH2 (kJ/mole) = 697 686 664 659 686 O2 C 664 O2 659 energy O2 CO2 + H2O + heat CO2 + H2O + heat CO2 + H2O + heat CO2 + H2O + heat What hybrid orbitals would be the best for the C-C bonds of cyclopropane? strain energy 60° H H Why are these C-C bonds weak? strain energy 116 kJ (27.7 kcal)/mol H H C H H C C H H 116 kJ 110 kJ (27.7 kcal)/mol (26.3 kcal)/mol H C C C H H H H H H C C H H C C H H H 42 kJ (10 kcal)/mol H H H H C C H C H H C C H H H H H H H no strain energy H C C H C H C C H H H H H C sp5 H C H H C C H H H A. Csp-Csp 180˚ B. Csp2-Csp2 120˚ C. Csp3-Csp3 109.5˚ D. Csp5-Csp5 <109.5˚ What hybrid orbitals does the carbon atom of cyclopropane use for the C-H bonds? strain energy 116 kJ (27.7 kcal)/mol H C H H C C H H H What hybrid orbitals does the carbon atom of cyclopropane use for the C-H bonds? strain energy 116 kJ (27.7 kcal)/mol H C H H C C H H H 2/6 s sp5 sp5 sp? sp? 10/6 p 1/6 s and 5/6 p 1/6 s and 5/6 p 2/6 s and 4/6 p 2/6 s and 4/6 p 4/6 s and 3 p sp5 H C H H C C H H H H C H H sp4 H C C H H sp? A. sp B. Csp2 C. sp3 2 10/6/2010 Why are cyclobutane and cyclopentane puckered? A. Bond angle strain. B. Torsional strain. How many different ways can a methyl group be attached to a cyclohexane ring? axial methyl group strain energy 116 kJ 110 kJ (27.7 kcal)/mol (26.3 kcal)/mol H C H H C C H H H H H H C C H H C C H H H 42 kJ (10 kcal)/mol H H H H C C H C H H C C H H H H H H H no strain energy H C C H C H C C H H H H H C C-C bond angles 60° 88° 105° 109.5° equatorial methyl group A. 1 B. 2 C. 3 D. 4 E. 6 F. 12 Which of the following methyl cyclohexanes is most stable? axial methyl group How many methylcyclohexanes are there? * * A B equatorial methyl group * Why is the axial conformation less stable than the equatorial conformation? Why is the twist boat conformation less stable than the equatorial or axial conformation? A. bond angle strain B. torsional strain C. steric strain (van der Waals) A. bond angle strain B. torsional strain C. steric strain (van der Waals) twist boat twist boat >21 kJ (5 kcal)/mol energy ΔG° energy ΔG° >21 kJ (5 kcal)/mol 7.28 kJ (1.74 kcal)/mol axial equatorial 7.28 kJ (1.74 kcal)/mol axial equatorial 1,3-diaxial 1,3-diaxial interaction 3 10/6/2010 Why is the twist boat conformation less stable than the equatorial or axial conformation? What is the approximate axial/equatorial Keq at RT? A. ≈ 0.031 A. bond angle strain B. torsional strain twist boat C. steric strain (van der Waals) Keq = >21 kJ (5 kcal)/mol energy ΔG° energy ΔG° B. ≈ 0.16 C. ≈ 1.0 D. ≈ 19 E. ≈ 230 F. ≈ 21000 when ΔG° = 5.7 KJ/mol then Keq = 101 10 19 = 107.28/5.7 = 101.28 ≈ 19 10 7.28 kJ (1.74 kcal)/mol axial equatorial 7.28 kJ (1.74 kcal)/mol axial equatorial How much of the equatorial conformation of methylcyclohexane would be present at room temperature? ΔG° = -RTln Keq 5% 95% 4 ...
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