Orgo Unit 8.1 Discussion

Orgo Unit 8.1 Discussion - delocalized onto the oxygen...

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Topic # 1: Explain why the carbonyl group can function as both a nucleophile and electrophile. According to David Klein in Organic Chemistry as a Second Language II , there are two factors that explain the electronics behind the carbonyl group. They are: 1.) Induction 2.) Resonance. These factors will explain the partial negative charge on the oxygen, which makes it nucleophilic, and the partial positive charge on the carbon, which makes it electrophilic. In terms of induction, as many have rightfully pointed out there, there is a strong electronegativity different between the oxygen atom (electronegativity = 3.5) and carbon (electronegative = 2.5). Consequently, oxygen is going to withdraw electron density from the carbon atom. This will leave oxygen with a partial negative charge and carbon with a partial positive charge. Another factor to consider is resonance. When we look at the different resonance structures for a carbonyl group, we see that the negative charge is
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Unformatted text preview: delocalized onto the oxygen atom, leaving it with a negative charge and the carbon atom with a positive charge. Again, that leaves the oxygen with an overall partial negative charge and the carbon with a partial positive charge. Klein also raised another interesting issue in his text as to why carbonyl groups are excellent electrophiles. He notes that the trigonal planar geometry of the carbonyl facilitates its ability to function as an electrophile, as it is easier for a nucleophile to attack the carbonyl. Taken together, the induction and resonance effects leave oxygen with a partial negative charge, and carbon with a partial positive charge. Accordingly, the oxygen atom on a carbonyl is very nucleophilic, and the carbon atom on a carbonyl is very electrophilic. Lastly, the overall geometry of carbonyl molecules also facilitate their functioning as a electrophile....
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This note was uploaded on 04/10/2011 for the course AAS 410.302.81 taught by Professor Thompson during the Spring '11 term at Johns Hopkins.

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