5 - 9/12/2011 Which anion is more stable, A or B? Why? Why...

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Unformatted text preview: 9/12/2011 Which anion is more stable, A or B? Why? Why do ethane and ethyne have very different pKas? pKa Ka 25 10-25 pKa 25 A ethyne 50 50 10-50 ethane B What hybrid orbitals are used to form the C-H bond in ethane, A. sp B. sp2 C. sp3? Are the electrons of the anion more stable in an sp atomic orbital? A. Yes B. No pKa pKa 25 25 ethyne sp 50 50 sp3 ethane hybrid orbitals linear (sp) tetrahedral (sp3) trigonal planar (sp2) Which compound has the strongest C-H bond A. ethyne B. ethane? success! pKa sp s p sp3 25 ethyne sp3 50 For larger molecules there is a lot of success but we are still working on the problem. from the application of quantum mechanics to H· we can derive all of the atomic orbitals as well as their hybrids. 1. 1. molecular orbital theory 2. valence bond theory (resonance structures) H· ethane quantum mechanics px s py for all atoms but H pz energy 1 9/12/2011 For a C=C bond choose the π-antibonding molecular orbital from the following list. resonance (Lewis) structures • valence bond theory H1s (A) C C σ-antibonding molecular orbital (B) • molecular orbital theory C C σ-bonding molecular orbital H1s (C) H Why is the bonding orbital more stable? CC π-antibonding molecular orbital H • molecular orbital theory What What role do antibonding orbitals play in your life? H H C H1s H1s bonding MO a molecular orbital theory Photochemistry! antibonding MO Orbital Energy π-bonding molecular orbital (D) Orbital Energy CC H Orbital Energy H • molecular orbital theory C C2p C C C C C2p C Can there be health problems associated with light? antibonding C DNA C C Csp2 Csp2 Orbital Energy C C bonding http://en.wikipedia.org/wiki/Pyrimidine_dimers 2 9/12/2011 What role does light play in your life? molecular orbital theory Choose the best Lewis (resonance) structure for formamide. O C C antibonding H C N H H formamide color C C H C N C I 3. add formal charges BH C H C Br 2. maximize bonding O H Si P S Cl 1. add electrons O A 34567 B C NOF N H C O C H H H O DH N C N H H H bonding vision molecular orbital theory C C Choose the best Lewis (resonance) structure for formamide. antibonding battery solar energy conversion C C O A H C O N H BH C H C C N H C O C H H H O DH N C N H H H bonding vision molecular orbital theory Choose the structure that is not a resonance structure of formamide. O C C antibonding H C N Resonance structures are different electronic configurations of the same structure. H H formamide C C O A H C O N H BH C H C C bonding C C H H H H C H O DH N C N H H H O O N C H O H N H O N H H H C N H H 3 9/12/2011 Choose the order that has the following structures arranged with respect to increasing stability. A 1 D 2 2 3 B 1 1 E 3 increasing stability 3 stability 1 2 2 F 3 stability H H H C 2 3 1 2 increasing stability O O N 1 increasing stability 1 increasing O C C stability increasing H 32 increasing N H H H C 3 N H H Arrange the following compounds in order of increasing stability. 1. maximum bonding (very important) 34567 B C NOF Si P S Cl 2. minimize charge separation. 3. charges on electronegative atoms. ⊕ charges on electropositive atoms. Br I increasing stability O H C O O N H H C H N H H C N H H H the complete story C O O O H N H H a true but incomplete story H C N H H a good story H C N H H an excellent story 4 ...
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