Alkenes as good nucleophiles

[deleted388502]

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Hi,

I got a passage recently that had an alkene and a carbene and asked which was the electrophile and nucleophile. I was very confused by why the alkene would be considered to be the nucleophile and have more electron density when the carbene literally has a lone pair on it.

Also confused why pi electrons and pi orbitals contribute to nucleophilicity in general.

Thanks!

 

[tdod]

Hi,

I got a passage recently that had an alkene and a carbene and asked which was the electrophile and nucleophile. I was very confused by why the alkene would be considered to be the nucleophile and have more electron density when the carbene literally has a lone pair on it.

Also confused why pi electrons and pi orbitals contribute to nucleophilicity in general.

Thanks!

π orbitals contribute to nucleophilicty b/c the π orbitals are located above and below the plane of the sigma bond. Because the sigma bond is directly between two nuclei, the π bond is above and below the 2 nuclei (see google images). Consequently, the π electrons are less stabilized by the nuclei and therefore more nucleophilic.

The carbene is electrophilic because it has an incomplete octet; in contrast, an alkene carbon has a complete octet.