Lesson 1
Why So High, Why So Low - The HOMO-LUMO View of Chemical Reactivity 1
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Prof. McBride, J. Michael, CHEM 125a, Freshman Organic Chemistry I, Fall 2008, YALE Open Courses: Yale University, Chemistry (Accessed 12/09/2014), http://oyc.yale.edu/chemistry/chem-125a/lecture-16 License: Creative Commons BY-NC-SA This lecture continues the discussion of the HOMO/LUMO view of chemical reactivity by focusing on ways of recognizing whether a particular HOMO should be unusually high in energy (basic), or a particular LUMO should be unusually low (acidic). The approach is illustrated with BH3, which is both acidic and basic and thus dimerizes by forming unusual "Y" bonds. The low LUMOs that make both HF and CH3F acidic are analyzed and compared underlining the distinction between MO nodes that derive from atomic orbitals nodes (AON) and those that are antibonding (ABN). Reaction of HF as an acid with OH- is shown to involve simultaneous bond-making and bond-breaking.

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