Pyramidal inversion: Difference between revisions

Revision as of 11:49, 6 June 2025

Latest revision as of 14:35, 6 June 2025

(4 intermediate revisions by one other user not shown)

Line 1:

{{Short description|Fluxional scientificprocess equationin trigonal-pyramidal molecules}}

{| class=floatright valign=center width="272px" style="margin-left:2em; margin-bottom:1ex; border: 1px solid darkgray; font-size:88.5%"

|-

|[[Image:Amine R-N.svg|96px]]

| style="font-size:200%" | ⇌ 

|[[Image:Amine N-R.svg|96px]]

|-

| colspan=3 |<small>'''InversionNitrogen of an amineinversion:''' The amine C₃ axis is horizontal, and; the pair of dots represent the nitrogen lone pair (on that axis). Note that the the two amine molecules are [[mirror symmetry|symmetric across a mirror plane]]. If the three R groups attached are all unique, then the amine is chiral; isolability depends on the [[Gibbs energy|free energy]] required to invert the molecule.</small>

|}

In [[chemistry]], '''pyramidal inversion''' (also '''umbrella inversion''') is a [[fluxional molecule|fluxional process]] in compounds with a [[pyramid]]al molecule, such as [[ammonia]] (NH₃) "turns inside out".<ref>{{ cite journal | author1 = Arvi Rauk|author2=[[Leland C. Allen]]|author3=[[Kurt Mislow]] | title = Pyramidal Inversion | journal = [[Angewandte Chemie International Edition]] | year = 1970 | volume = 9 | issue = 6 | pages = 400–414 | doi = 10.1002/anie.197004001}}</ref><ref name="ReferenceA">{{GoldBookRef|file=P04956|title=Pyramidal inversion}}</ref> It is a [[Molecular vibration|rapid oscillation]] of the atom and substituents, the molecule or ion passing through a [[Trigonal planar molecular geometry|planar]] [[transition state]].<ref>{{ cite journal | author = J. M. Lehn | author-link = Jean-Marie Lehn | title = Nitrogen Inversion: Experiment and Theory | journal = Fortschr. Chem. Forsch. | year = 1970 | volume = 15 | pages = 311–377 | doi = 10.1007/BFb0050820}}</ref> For a compound that would otherwise be [[Chirality (chemistry)|chiral]] due to a [[stereocenter]], pyramidal inversion allows its [[enantiomer]]s to [[racemize]]. The general phenomenon of pyramidal inversion applies to many types of molecules, including [[carbanion]]s, [[amines]], [[phosphane|phosphines]], [[arsine]]s, [[stibine]]s, and [[sulfoxide]]s.<ref>{{cite journal |author=Arvi Rauk |author2=Leland C. Allen |author3=Kurt Mislow |year=1970 |title=Pyramidal Inversion |journal=Angewandte Chemie International Edition |volume=9 |issue=6 |pages=400–414 |doi=10.1002/anie.197004001}}</ref><ref name="ReferenceA" />

Line 7 ⟶ 15:

==Nitrogen inversion==

| colspan=3 align=right |[[Image:Nitrogen-inversion-3D-balls.png|thumb|250px|Nitrogen inversion in ammonia]]

{| class=floatright valign=center width="272px" style="margin-left:2em; margin-bottom:1ex"

| colspan=3 align=right |[[Image:Nitrogen-inversion-3D-balls.png|thumb|250px|Nitrogen inversion in ammonia]]

|-

|[[Image:Amine R-N.svg|96px]]

| style="font-size:200%" |&nbsp;⇌&nbsp;

|[[Image:Amine N-R.svg|96px]]

|-

| colspan=3 |<small>'''Inversion of an amine:''' The amine C₃ axis is horizontal, and the pair of dots represent the nitrogen lone pair (on that axis). Note that the the two amine molecules are [[mirror symmetry|symmetric across a mirror plane]]. If the three R groups attached are all unique, then the amine is chiral; isolability depends on the [[Gibbs energy|free energy]] required to invert the molecule.</small>

|}

Pyramidal inversion in [[nitrogen]] and [[amine]]s is known as '''nitrogen inversion'''.<ref>{{Cite journal|last1=Ghosh|first1=Dulal C.|last2=Jana|first2=Jibanananda|last3=Biswas|first3=Raka|date=2000|title=Quantum chemical study of the umbrella inversion of the ammonia molecule|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/1097-461X%282000%2980%3A1%3C1%3A%3AAID-QUA1%3E3.0.CO%3B2-D|journal=International Journal of Quantum Chemistry|language=en|volume=80|issue=1|pages=1–26|doi=10.1002/1097-461X(2000)80:1<1::AID-QUA1>3.0.CO;2-D|issn=1097-461X|url-access=subscription}}</ref> It is a [[Molecular vibration|rapid oscillation]] of the nitrogen atom and substituents, the nitrogen "moving" through the plane formed by the substituents (although the substituents also move - in the other direction);<ref>{{Greenwood&Earnshaw2nd|page=423}}</ref> the molecule passing through a [[Trigonal planar molecular geometry|planar]] [[transition state]].<ref>{{ cite journal | author = J. M. Lehn | author-link = Jean-Marie Lehn | title = Nitrogen Inversion: Experiment and Theory | journal = [[Fortschritte der Chemischen Forschung|Fortschr. Chem. Forsch.]] | year = 1970 | volume = 15 | pages = 311–377 | doi = 10.1007/BFb0050820 }}</ref> For a compound that would otherwise be [[Chirality (chemistry)|chiral]] due to a nitrogen [[stereocenter]], nitrogen inversion provides a low energy pathway for [[racemization]], usually making [[chiral resolution]] impossible.<ref>{{March6th|pages=142–145}}</ref>

Line 35:

==References==

{{ReflistClear-right}}

<references/>

[[Category:Physical chemistry]]