Trifluoromethyl Cation on:
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The trifluoromethyl cation is a molecular
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
with a formula of . It is a carbocation
A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium , methanium and vinyl cations. Occasionally, carbocations that bear more than one positively charged carbon atom are also encoun ...
due to its positively charged carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
atom. It is part of the family of carbenium ion
A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with a trivalent carbon that bears a +1 formal charge.
In older literature the name carbonium ion was used for this class, but now it refers exclusively ...
s, with three fluorine atoms as substituents
A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...
in place of its hydrogen atoms.
Stability
Compared tomethenium
In organic chemistry, methenium (also called methylium, carbenium, methyl cation, or protonated methylene) is a cation with the formula . It can be viewed as a methylene radical (:) with an added proton (), or as a methyl radical (•) with one ...
(the simplest carbenium ion
A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with a trivalent carbon that bears a +1 formal charge.
In older literature the name carbonium ion was used for this class, but now it refers exclusively ...
), trifluoromethyl cation is more stable due to the presence of fluorine atoms. The fluorine atoms have lone pairs
In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lo ...
of electrons overlapping with the carbon atom. These electrons stabilize the positive charge of the central carbon atom, stabilizing the molecule as a whole. The overlap is effective due to the size of fluorine's p orbital in the molecule.
Synthesis
While electron-donating fluorine lone pairs are present, it does not exist as its own. The production of a cation has been described as "extremely hard". The first relevant reagent, a diaryl(trifluoromethyl) sulfonium salt () was developed in 1984 by reaction of an aryltrifluoromethyl sulfoxide 1 with followed by reaction with an electron-rich arene. Now the reaction of the source of the cation usually uses 5-(trifluoromethyl)dibenzothiophenium tetrafluoroborate as the reagent.{{Cite journal, last=Barata‐Vallejo, first=Sebastián, last2=Lantaño, first2=Beatriz, last3=Postigo, first3=Al, date=2014, title=Recent Advances in Trifluoromethylation Reactions with Electrophilic Trifluoromethylating Reagents, url=https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.201404005, journal=Chemistry – A European Journal, language=en, volume=20, issue=51, pages=16806–16829, doi=10.1002/chem.201404005, issn=1521-3765
References