Diethynylbenzene Dianion on:
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organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
, a diethynylbenzene dianion is an anion consisting of two ethynyl anions as substituent
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 ...
s on a benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
ring. With the chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
, three positional isomer
In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term meta ...
s are possible, differing in the relative positions of the two substituents around the ring:
*''ortho''-diethynylbenzene dianion
*''meta''-diethynylbenzene dianion
*''para''-diethynylbenzene dianion
The gaseous state of all three anions are of theoretical interest. They have been generated by decarboxylation
Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...
of benzene di propynoic acids, using the technique of mass spectrometry
Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...
. The three isomers of the dianion are the three strongest known superbases ever, with the ''ortho'' isomer being the strongest, with a proton affinity of . The ''meta'' isomer is the second-strongest, and the ''para'' isomer is the third-strongest.
Observation
These dianions were generated in a linear quadrupole ion-trap mass spectrometer.Electrospray ionization
Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions using an electrospray in which a high voltage is applied to a liquid to create an aerosol. It is especially useful in producing ions from macromolecules becaus ...
(ESI) of the diacid precursor results in the dicarboxylate dianion 6H4(C3O2)2sup>2− by loss of two hydrogen atoms, identified spectrometrically by its mass-to-charge ratio
The mass-to-charge ratio (''m''/''Q'') is a physical quantity relating the ''mass'' (quantity of matter) and the ''electric charge'' of a given particle, expressed in units of kilograms per coulomb (kg/C). It is most widely used in the electrody ...
(''m''/''z'') of 106. This dianion was mass-selected and then subjected to collision-induced dissociation
Collision-induced dissociation (CID), also known as collisionally activated dissociation (CAD), is a mass spectrometry technique to induce fragmentation of selected ions in the gas phase. The selected ions (typically molecular ions or protonate ...
(CID), resulting in the consecutive loss of two carbon dioxide molecules to form the diethynyl dianion 6H4(C2)2sup>2− at ''m''/''z'' = 62. For the ''ortho'' isomer, the reaction process is as follows, with the other isomers following an analogous process depending on the isomer of the original diacid:
Reactions
Reactions of the gas-phase dianions were studied by reacting with a small quantity of various reagents added to the helium carrier gas in the spectrometer. For example, reaction with deuterium oxide ( heavy water) produced the singly-deuterated monoanion C6H4(C2D)() identified as ''m''/''z'' = 126. Reaction with benzene produced the phenyl anion (''m''/''z'' = 77) highlighting the extreme basicity of the dianion. Attempted reaction withdeuterium
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
gas and deuterated methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
was not successful despite the favourable thermodynamics; the authors attribute this to the high activation barrier
In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...
for proton abstraction from those substrates.
Basicity
All three isomers aresuperbasic
SuperBASIC is an advanced variant of the BASIC programming language with many structured programming additions. It was developed at Sinclair Research by Jan Jones during the early 1980s. Originally SuperBASIC was intended as the BASIC interprete ...
. According to calculations, ''ortho''-diethynylbenzene dianion is the strongest superbase and has a proton affinity of . The ''meta'' isomer is the second-strongest, and the ''para'' isomer is the third. All three are readily able to accept any proton to its ethynyl tails, from almost any compound. All three isomers function as superbases better than helonium
The helium hydride ion or hydridohelium(1+) ion or helonium is a cation (positively charged ion) with chemical formula HeH+. It consists of a helium atom bonded to a hydrogen atom, with one electron removed. It can also be viewed as protonated ...
does as a superacid.
See also
*Lithium monoxide anion
Lithium monoxide anion (LiO−) is a superbase existing in the gas phase. It was the strongest known base until 2008, when the isomeric diethynylbenzene dianions were determined to have a higher proton affinity. The methanide ion CH3− was the ...
References
{{Reflist Acetylides Anions Benzene derivatives Superbases