aromaticity question

[duke2121]

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I can't copy the image since I no longer have Chad's videos,but its cyclopentadiene with the top carbon having a lone pair and a negative charge. First, since that carbon is sp3 is the structure nonaromatic?

I think chad has it as aromatic since it has 6pi electrons.

 

[MatthewCC]

The carbon is sp2 not sp3, it's bonded to 2 carbons and 1 hydrogen and there is one lone pair. The lone pair is in a p orbital, not a hybridized orbital. So those electrons in the p orbital are delocalized and count for aromaticity. 2*2 for the 2 pi bonds = 4, + the 2 delocalized e- is 6 which means the structure is aromatic.

 

[duke2121]

The carbon is sp2 not sp3, it's bonded to 2 carbons and 1 hydrogen and there is one lone pair. The lone pair is in a p orbital, not a hybridized orbital. So those electrons in the p orbital are delocalized and count for aromaticity. 2*2 for the 2 pi bonds = 4, + the 2 delocalized e- is 6 which means the structure is aromatic.

Thanks, I was just confused because in a CH3- its sp3 right?

 

[SN1]

If you have an atom with just ONE lone pair and that atom doesn't have a double bond, then the lone pair does NOT count as a region of electron domain for hybridization and instead count as 2 pi electron.

If you have an atom with two lone pairs, then only one of the will count as pi electron while the other pair count as electron domain for hybridization.

 

[duke2121]

If you have an atom with just ONE lone pair and that atom doesn't have a double bond, then the lone pair does NOT count as a region of electron domain for hybridization and instead count as 2 pi electron.

If you have an atom with two lone pairs, then only one of the will count as pi electron while the other pair count as electron domain for hybridization.

Ok, so for tetrahydrofuran the oxygen with 2 lone pairs, the hybridization of the oxygen is sp3? but if its in a conjugated system its sp2?

 

[MatthewCC]

Yep

 

[SN1]

Ok, so for tetrahydrofuran the oxygen with 2 lone pairs, the hybridization of the oxygen is sp3? but if its in a conjugated system its sp2?

Exactly. The hybridization of the oxygen atom would be sp2 and the other lone pair would count as pi electron.