Exceptions to the hybridization rules

[inaccensa]

http://www.youtube.com/watch?v=ns4Py96Bkn8&NR=1


Here the rule of Determining Hybridization are as follows

Hybridization + # of sigma bonds + # of lone pairs

However, there is an exception according to the above video

If an atom has one or more lone pairs and is attached to a Sp2 atom, it must be Sp2!!! Do we have to know this exception? Can anyone please explain how exactly does this work?

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[maverick09]

this is a very important rule and is definitely fair game for the mcat.

as you said, if an atom has one or more lone pairs and is attached to a Sp2 atom, it must be Sp2.

let's illustrate this using proteins, specifically peptide bonds. these bonds are planar and have double bond character due to the resonance experienced via nitrogen's lone pair. as a refresher, a peptide bond is formed between two amino acids in a condensation reaction between the carboxylate group of one amino acid and the amino group of the other amino acid. the resulting bond is between a carbonyl carbon (sp2 hybridized) and a nitrogen with a lone pair.

the lone pair can be brought down and form a double bond between the carbon and nitrogen thus resulting in nitrogen being sp2. essentially, it is just electron pushing

hope this helped

 

[thebillsfan]

this is a very important rule and is definitely fair game for the mcat.

as you said, if an atom has one or more lone pairs and is attached to a Sp2 atom, it must be Sp2.

let's illustrate this using proteins, specifically peptide bonds. these bonds are planar and have double bond character due to the resonance experienced via nitrogen's lone pair. as a refresher, a peptide bond is formed between two amino acids in a condensation reaction between the carboxylate group of one amino acid and the amino group of the other amino acid. the resulting bond is between a carbonyl carbon (sp2 hybridized) and a nitrogen with a lone pair.

the lone pair can be brought down and form a double bond between the carbon and nitrogen thus resulting in nitrogen being sp2. essentially, it is just electron pushing

hope this helped

so you would still call that nitrogen atom sp2, even though it *isnt* sp2 all the time but only when its resonating?

 

[Chuck's Right Foot]

so you would still call that nitrogen atom sp2, even though it *isnt* sp2 all the time but only when its resonating?

Things are always resonating. Which is why bond length is always the average of the various bonds given by the different resonance structures.

 

[wanderer]

so you would still call that nitrogen atom sp2, even though it *isnt* sp2 all the time but only when its resonating?

Resonance is a bit of a misnomer, since in physical resonance, it forms a stable mixture of the the different contributing structures, and there isn't an equilibrium.

 

[Baylor2012]

is this an organic chem topic?

 

[maverick09]

yup...it could also be an integrated bio/ochem passage if they use biomolecules to exhibit this exception (ie amino acids)