:Trigonal planar molecular geometry

{{Short description|Molecular geometry of symmetry D_3h}}

{{Infobox molecular geometry |

Image_File=Trigonal-3D-balls.png|

Symmetry_group= D_3h |

Atom_direction=3 |

Bond_angle=120° |

mu=0 |

Examples=SO₃

}}

Image:Boron-trifluoride-3D-vdW.png, an example of a molecule with trigonal planar geometry.]]

In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane.{{Cite book |last=March |first=Jerry |url=https://www.worldcat.org/oclc/10998226 |title=Advanced organic chemistry : reactions, mechanisms, and structure |date=1985 |publisher=Wiley |isbn=0-471-88841-9 |edition=3rd |location=New York |oclc=10998226}} In an ideal trigonal planar species, all three ligands are identical and all bond angles are 120°. Such species belong to the point group D_3h. Molecules where the three ligands are not identical, such as H₂CO, deviate from this idealized geometry. Examples of molecules with trigonal planar geometry include boron trifluoride (BF₃), formaldehyde (H₂CO), phosgene (COCl₂), and sulfur trioxide (SO₃). Some ions with trigonal planar geometry include nitrate ({{chem|NO|3|−}}), carbonate ({{chem|CO|3|2−}}), and guanidinium ({{chem|C(NH|2|)|3|+}}). In organic chemistry, planar, three-connected carbon centers that are trigonal planar are often described as having sp² hybridization.{{cite book|last1=Holleman|first1=A. F.|last2=Wiberg|first2=E.|title=Inorganic Chemistry|publisher=Academic Press|location=San Diego|date=2001|isbn=0-12-352651-5}}{{cite book|first1=G. L.|last1=Miessler|first2=D. A.|last2=Tarr|title=Inorganic Chemistry|year=2004|edition=3rd|publisher=Pearson/Prentice Hall|isbn=0-13-035471-6|url-access=registration|url=https://archive.org/details/inorganicchemist03edmies}}

Nitrogen inversion is the distortion of pyramidal amines through a transition state that is trigonal planar.

Pyramidalization is a distortion of this molecular shape towards a tetrahedral molecular geometry. One way to observe this distortion is in pyramidal alkenes.