Planar compounds trifluoride

In each case the configuration around the boron changes from trigonal planar to tetrahedral on adduct formation. Because of this ability to form additional compounds, boron trifluoride is an important catalyst and is used in many organic reactions, notably polymerisation, esterification, and Friedel-Crafts acylation and alkylations. 

Boron is a Group HTA element that forms many covalent compounds by bonding to three other atoms. Typical examples include boron trifluoride, BF3 (mp — 127°C) boron trichloride, BCI3 (mp — 107°C) boron tribromide, BBr3 (mp -46°C) and boron triiodide, BI3 (mp 50°C). All are trigonal planar nonpolar molecules. 

Boron, a group IIIA element, has only three valence electrons. In the compound boron trifluoride (BF3) these three electrons are shared with three fluorine atoms. As a result, the boron atom in BF3 has only six electrons (three bonding pairs) around it. Maximum separation of three bonding pairs occurs when they occupy the comers of an equilateral triangle. Consequently, in the boron trifluoride molecule the three fluorine atoms lie in a plane at the comers of an equilateral triangle (Fig. 1.36). Boron trifluoride is said to have a trigonal planar structure. The bond angles are 120°. 

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