Ch_322a_3.05

Ch_322a_3.05 - level of the bonded state with the number in...

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Carbon Bond Heterolysis Processes: Carbocations and Carbanions When a bond to carbon is broken heterolytically, the carbon may carry either a positive (carbocation) or negative (carbanion) charge. Modes of Heterolytic Bond Cleavage C:X ! + !" C + + X: - a carbocation C:Y ! + !" C: - + Y + a carbanion
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Formal Charges Carbocations have only six electrons in the valence or bonding level and are electron-deficient. The charge on carbon can be determined by a simple calculation. Step One: Determine how many of the valence electrons "belong" to carbon. For each pair of bonding electrons , one "belongs" to carbon. All nonbonding electrons in the valence level "belong" to carbon. C + a carbocation In a carbocation, only 3 of the 6 bonding electrons "belong" to the carbon. There are no nonbonding electrons.
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Step Two: Compare the number of "owned" electrons in the valence
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Unformatted text preview: level of the bonded state with the number in the atomic state. Atomic carbon has 4 electrons in the valence level . Since in the carbocation, only 3 electrons belong to carbon, there is a deficiency of one electron (a formal charge imbalance at carbon). Therefore, there is a formal charge of +1 on carbon. Carbanions C:-a carbanion Three of the bonding electrons and the two nonbonding electrons belong to carbon. Calculation of Formal Charge Carbanions have 6 bonding and two nonbonding electrons in the valence level, and have a formal charge of -1 . Since atomic carbon has 4 electrons in the valence level while 5 of the 8 valence electrons in the carbanion belong to carbon, there is a surplus of one electron in the bonded state. The formal charge is -1 ....
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_3.05 - level of the bonded state with the number in...

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