classes_Spring08_172ID39_ProblemSet3 - Chemistry 172/273...

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1 Chemistry 172/273 Problem Set #3 Due on Friday, May 23, in class Spring 2008 Note : Do not use a pencil. Use black ink only. Try to write as neatly as possible. If I don’t understand your handwriting, you will not get any points. 1 . a) Consider the H 3 + ion in which H is at each corner of an equilateral triangle. Using the SALC of the 3 hydrogen 1s atomic orbitals, construct a molecular diagram for H 3 + , label the orbitals with the apropiate Mulliken symbols, and fill the energy levels with the apropiate number of electrons. b) How many fundamental vibrations do you expect for the cyclic H 3 + ion? What are the symmetries of the vibrations in H 3 + and which are infrared and which are Raman active? 2 . Cyclopropane, C 3 H 6 , is a remarkably stable molecule (m.p. -127.6 °C, b.p. -32.7 °C), despite the extreme ring strain. Indeed, from a traditional valence bond approach, assuming sp 3 -hybridized carbon atoms, one might wonder why it exists at all. A delocalized MO model suggests that the ring receives stabilization through p π -bonding, a result hardly expected for an alkane. Based on its photoelectron spectrum (cf. D. W. Turner, C. Baker, A. D. Baker, and C. R. Brundle, Molecular Photoelectron Spectroscopy , Wiley-Interscience, London, p. 203), the electronic structure of cyclopropane can be written as ( σ C-H ) 2 ( σ C-H ) 4 ( π C-C ) 2 ( σ C-C ) 2 ( π C-C ) 4 ( σ C-H
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This note was uploaded on 10/12/2009 for the course CHEM C172 taught by Professor Zink,j during the Spring '08 term at UCLA.

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classes_Spring08_172ID39_ProblemSet3 - Chemistry 172/273...

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