Cation-pi interactions: Difference between revisions

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[[Image:Benzene Orbitals.png|frame|Credit: [http://en.wikipedia.org/wiki/File:Benzene_Orbitals.svg Wikimedia Commons].]]

Six-carbon aromatic rings occur in the sidechains of 3 of the [[amino acids|20 standard amino acids]]: namely [[Amino_Acids#Phenylalanine|phenylalanine]], [[Amino_Acids#Tryptophan|tryptophan]], and [[Amino_Acids#Tyrosine|tyrosine]]. ~~The~~ [http://en.wikipedia.org/wiki/P-orbital atomic ~~p orbitals~~] ~~of the carbons overlap~~ sideways~~, forming~~ a [http://en.wikipedia.org/wiki/Conjugated_system conjugated] pi (π) orbital system~~, or~~ pi ~~cloud~~ of [http://en.wikipedia.org/wiki/Delocalized_electron delocalized ~~electrons~~]<ref name="lillya">[[User:Eric Martz|Eric Martz]] thanks [http://www.cns.umass.edu/faculty/directory/c-peter-lillya Peter Lillya] for help ~~with terminology~~.</ref> ('''see Figure at right'''). The pi clouds on each face of the ring have a partial negative charge, while the edge of the ring has a compensating partial positive charge ('''see Figure above'''). Proximity of a positive charge to one face of the ring induces further polarization, and in the proper conformation produces an electrostatic interaction called a '''cation-pi interaction'''.

The cation-pi interaction is a stabilizing electrostatic interaction of a cation with the polarizable pi electron cloud of an aromatic ring.

Six-carbon aromatic rings occur in the sidechains of 3 of the [[amino acids|20 standard amino acids]]: namely [[Amino_Acids#Phenylalanine|phenylalanine]], [[Amino_Acids#Tryptophan|tryptophan]], and [[Amino_Acids#Tyrosine|tyrosine]]. One [http://en.wikipedia.org/wiki/P-orbital p atomic orbital] on each aromatic carbon overlaps in a pi ("sideways") fashion with its two neighbors to form a [http://en.wikipedia.org/wiki/Conjugated_system conjugated] pi (π) orbital system.

The pi electrons of aromatic rings comprise [http://en.wikipedia.org/wiki/Delocalized_electron delocalized] annular clouds above and below the ring plane ('''see Figure at right'''). Proximity of a positive charge to one face of the ring attacts and polarizes the pi electron cloud. In the proper conformation, this proximity forms an energetically significant '''cation-pi''' interaction.<ref name="lillya">[[User:Eric Martz|Eric Martz]] thanks [http://www.cns.umass.edu/faculty/directory/c-peter-lillya Peter Lillya] for help writing this paragraph.</ref> .

Cation-pi interactions: Difference between revisions

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 [[Image:Benzene Orbitals.png|frame|Credit: [http://en.wikipedia.org/wiki/File:Benzene_Orbitals.svg Wikimedia Commons].]]
-Six-carbon aromatic rings occur in the sidechains of 3 of the [[amino acids|20 standard amino acids]]: namely [[Amino_Acids#Phenylalanine|phenylalanine]], [[Amino_Acids#Tryptophan|tryptophan]], and [[Amino_Acids#Tyrosine|tyrosine]]. The [http://en.wikipedia.org/wiki/P-orbital atomic p orbitals] of the carbons overlap sideways, forming a [http://en.wikipedia.org/wiki/Conjugated_system conjugated] pi (&pi;) orbital system, or pi cloud of [http://en.wikipedia.org/wiki/Delocalized_electron delocalized electrons]<ref name="lillya">[[User:Eric Martz|Eric Martz]] thanks [http://www.cns.umass.edu/faculty/directory/c-peter-lillya Peter Lillya] for help with terminology.</ref> ('''see Figure at right'''). The pi clouds on each face of the ring have a partial negative charge, while the edge of the ring has a compensating partial positive charge ('''see Figure above'''). Proximity of a positive charge to one face of the ring induces further polarization, and in the proper conformation produces an electrostatic interaction called a '''cation-pi interaction'''.
+The cation-pi interaction is a stabilizing electrostatic interaction of a cation with the polarizable pi electron cloud of an aromatic ring.
+Six-carbon aromatic rings occur in the sidechains of 3 of the [[amino acids|20 standard amino acids]]: namely [[Amino_Acids#Phenylalanine|phenylalanine]], [[Amino_Acids#Tryptophan|tryptophan]], and [[Amino_Acids#Tyrosine|tyrosine]]. One [http://en.wikipedia.org/wiki/P-orbital p atomic orbital] on each aromatic carbon overlaps in a pi ("sideways") fashion with its two neighbors to form a [http://en.wikipedia.org/wiki/Conjugated_system conjugated] pi (&pi;) orbital system.
+The pi electrons of aromatic rings comprise [http://en.wikipedia.org/wiki/Delocalized_electron delocalized] annular clouds above and below the ring plane ('''see Figure at right'''). Proximity of a positive charge to one face of the ring attacts and polarizes the pi electron cloud. In the proper conformation, this proximity forms an energetically significant '''cation-pi''' interaction.<ref name="lillya">[[User:Eric Martz|Eric Martz]] thanks [http://www.cns.umass.edu/faculty/directory/c-peter-lillya Peter Lillya] for help writing this paragraph.</ref> .
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