CH_318N_Lecture9-08_Spring_08

CH_318N_Lecture9-08_Spring_08 - 1 Chemistry 318N More on...

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Unformatted text preview: 1 Chemistry 318N More on Aromatics Lecture 9 February 14, 2008 Chemistry 318N First Midterm Exam c When: Wednesday, 2/20 c When: 7-9PM c Where: WEL 1.308 c What: Covers material through this Thursday c Review: 2/18 6:00 PM Lecture Room c Review: 2/19 6:00 PM Painter 3.02 c Practice: Exams will be posted on the web site c Pleasebring pencils, an eraser and a calculator only and . Do a good job!!! 2 Chemistry 318N 120 kJ/mol 360 kJ/mol 208 kJ/mol 3 x cyclohexene Resonance energy 152 kJ/mol Why???? Chemistry 318N 1. But I hate MO stuff it is confusing f The answer comes from MO Theory 2. How do you even know how many MOs there are?? 3. How do you know the relative energies of these MOs??? 3 Chemistry 318N MO Theory 2 s atomic orbitals 2 molecular orbitals Chemistry 318N Hydrogen Molecular Orbitals 1. Conservation of numbers of orbitals 2. Energy Symmetry 4 Chemistry 318N Bonding and antibonding molecular orbitals in hydrogen (H 2 ). A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed. An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed. Chemistry 318N 5 Chemistry 318N Ethylene C C H H H H Ethene 2 p atomic orbitals 2 molecular orbitals Chemistry 318N 1,3-butadiene 6 Chemistry 318N For Cyclic Structures Frost Circlesa Great Trick c Inscribe a polygon of the same number of sides as the ring to be examined such that one of the vertices is at the bottom of the ring c The relative energies of the MOs in the ring are given by where the vertices touch the circle c The MOs below the horizontal line through the center of the ring are bonding MOs on the horizontal line are nonbonding MOs above the horizontal line are antibonding MOs Chemistry 318N 7 Chemistry 318N Cyclo- butadiene Antibonding Bonding 4 electrons; bonding orbital is filled; other 2 electrons singly occupy two nonbonding orbitals -MOs of Cyclobutadiene (square planar) Chemistry 318N structure of a stabilized derivative is characterized...
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CH_318N_Lecture9-08_Spring_08 - 1 Chemistry 318N More on...

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