Resonance Explanation.pdf

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CHE 118A
Vahid Eskandari

Guide to Drawing Resonance Structures 1. Do not violate the octet rule!!! (DO NOT HAVE 5 BONDS TO CARBON!!!) 2. The overall charge of a molecule should not change—atoms may have charges, but the net charge of the entire molecule should not change. 3. Place resonance structures inside brackets ([ ])↔anto separate each structure 4. Do not breakσ bonds! (e.g. do not break C-C, C-H, C-O, or C-N single bonds) 5. Carbon can have 6 or 8 electrons. Nitrogen will sometimes have 6 electrons, but this is very rare(e.g. in the minor resonance structure of the nitrosyl cation, NO , nitrogen has six electrons). In general, however, nitrogen should have eight electrons around it. O, F, Cl, Br, and I must always have 8 electrons. Structures with a maximum number of octets are preferred. 6. Charges will be preferentially located on atoms of compatible electronegativity. For example, oxygen is more electronegative than carbon; therefore, a negative charge will preferentially be placed on oxygen rather than carbon in the dominant resonance structure. 7. Structures with a minimum of charge separation are preferred. This rule is derived from Coulomb’s law, which states that the separation of charges requires energy. Hence, neutral structures are better than dipolar ones. Minimize the number of charges you have in a resonance structure. 8. Unless starting with a radical, move electrons in pairs, using a double-headed arrow. 9. Do not “jump” lone pairs from one atom to another. Lone pairs can bπ bonds or π bonds can become lone pairπ Bonds can migrate from one side of a carbon atom to another.
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