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CH 221 Tips on Writing Resonance Structures

CH 221 Tips on Writing Resonance Structures - • If the...

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Chemistry 221 College of the Holy Cross Prof. Gail Edwards Organic Chemistry I Spring 2008 Tips on Writing Resonance Structures In order to write good resonance structures of neutral organic molecules or of organic cations or anions, pay attention to the following: Move electrons, not atoms. Keep the arrangement of atoms the same. Move only nonbonded electrons or electrons in multiple bonds. Move electrons only where is room for them or where room can be made for them by breaking another bond. Remember that Period 2 atoms in resonance structures can have fewer than eight electrons but not more than eight electrons. Move electrons only to adjacent atoms not to distant atoms. Show the movement of electrons with curved arrows. If the movement of electrons results in charge, show the charge.
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Unformatted text preview: • If the movement of electrons results in a change in the position of the charge, show that charge. • Avoid trivial resonance structures. For example do not break a carbon-carbon double bond simply to form a positive and negative charge on the two atoms. This just creates charge without adding stability. • In general the best resonance structures are those which have 1. complete octets 2. the maximum number of bonds 3. the least separation of charge 4. the negative charge on the more electronegative atom 5. the positive charge on the more electropositive atom The destabilizing effect of a positive charge on an electronegative atom can be overridden if such an arrangement results in complete octets....
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