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Quaternary ammonium cation. The R groups may be the same or different alkyl or aryl groups. Also, the R groups may be connected. In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure [NR 4] +, where R is an alkyl group, an aryl group [1] or organyl group.
In chemistry, a quaternary compound is a compound consisting of exactly four chemical elements. In another use of the term in organic chemistry , a quaternary compound is or has a cation consisting of a central positively charged atom with four substituents, especially organic ( alkyl and aryl ) groups, discounting hydrogen atoms.
Tetramethylammonium (TMA) is the simplest quaternary ammonium cation. It has the chemical formula [Me 4 N] + and consists of four methyl groups (−CH 3, denoted Me) attached to a central nitrogen atom. The cation is isoelectronic with neopentane (Me 4 C). It is positively-charged and can only be isolated in association with a counter-ion.
Like other quaternary ammonium cations, TPA is prepared by the alkylation of the corresponding ammonia analogue, tripropylamine. Treatment of the amine with a primary propyl halide such as n-bromopropane yields the corresponding TPA halide salt in a Menshutkin reaction: (C 3 H 7) 3 N + C 3 H 7 Br → (C 3 H 7) 4 N + Br −
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Tetramethylammonium hydroxide (TMAH or TMAOH) is a quaternary ammonium salt with molecular formula N(CH 3) 4 + OH −. It is commonly encountered in form of concentrated solutions in water or methanol. TMAH in solid state and its aqueous solutions are all colorless, but may be yellowish if impure.
Tetraethylammonium (TEA) is a quaternary ammonium cation with the chemical formula [Et 4 N] +, consisting of four ethyl groups (−C 2 H 5, denoted Et) attached to a central nitrogen atom. It is a counterion used in the research laboratory to prepare lipophilic salts of inorganic anions.
Tetrabutylammonium is a quaternary ammonium cation with the formula [N(C 4 H 9) 4] +, also denoted [NBu 4] + (where Bu = butyl group). It is used in the research laboratory to prepare lipophilic salts of inorganic anions. Relative to tetraethylammonium derivatives, tetrabutylammonium salts are more lipophilic but crystallize less readily.