Boron trifluoride

Boron trifluoride (BF₃) is a colorless, toxic gas whose electron-deficient boron atom makes it a strong Lewis acid and useful catalyst.

Lewis acid: An electron-pair acceptor in the Lewis definition of acids and bases. BF₃ accepts electron pairs, the defining behavior that underlies its catalytic action.
Friedel–Crafts reaction: An electrophilic aromatic substitution that adds an alkyl or acyl group to an aromatic ring. BF₃ can activate reagents as a Lewis acid in Friedel–Crafts chemistry.
Boron: A chemical element with atomic number 5, occurring in several forms and compounds. Boron’s three valence electrons leave it electron-deficient in BF₃.
Boron trichloride: A trigonal planar boron halide with formula BCl₃ and Lewis-acid behavior. BCl₃ is a close halide analogue whose Lewis acidity differs from BF₃’s.
Lewis base: An electron-pair donor in the Lewis definition of acids and bases. Lewis bases donate electron pairs to boron, forming adducts with BF₃.
Polymerization: A chemical process that joins small molecules into large molecules made of repeating units. BF₃ initiates or catalyzes polymerization of several electron-rich monomers.
Fluorine: A highly reactive chemical element with atomic number 9 and the highest electronegativity. Fluorine strongly polarizes each B–F bond in BF₃.
Boron tribromide: A boron halide with formula BBr₃, used as a Lewis acid and demethylating reagent. BBr₃ offers a heavier-halide comparison and is often used for ether cleavage.
Boron trifluoride–diethyl etherate: A BF₃–diethyl ether complex commonly used as a liquid source of boron trifluoride. Ether coordinates to BF₃ and makes the volatile gas easier to handle.
Cationic polymerization: A chain-growth polymerization in which positively charged chain ends add monomers. BF₃-based initiators generate cationic chains from suitable monomers.

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