Diethynylbenzene dianion

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In organic chemistry, a diethynylbenzene dianion is a structure consisting of two ethynyl anions as substituents on a benzene ring. With the chemical formula C
6H
4C2−
4, three positional isomers 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 anions are of theoretical interest. They have been generated by decarboxylation of benzene dipropynoic acids, using the technique of mass spectrometry.[1][2]

Observation[]

These dianions were generated in a linear quadrupole ion-trap mass spectrometer. Electrospray ionization (ESI) of the diacid precursor results in the dicarboxylate dianion [C6H4(C3O2)2]2− by loss of two hydrogen atoms, identified spectrometrically by its mass-to-charge ratio (m/z) of 106. This dianion was mass-selected and then subjected to collision-induced dissociation (CID), resulting in the consecutive loss of two carbon dioxide molecules to form the diethynyl dianion [C6H4(C2)2]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:

Preparation of o-diethynylbenzene dianion from the o-dipropynoic acid precursor

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)(C−
2) identified as m/z = 126. Reaction with benzene produced the phenyl anion (m/z = 77) highlighting the extreme basicity of the dianion. Attempted reaction with deuterium gas and deuterated methane was not successful despite the favourable thermodynamics; the authors attribute this to the high activation barrier for proton abstraction from those substrates.[1]

Basicity[]

All three isomers are superbasic. According to calculations, ortho-diethynylbenzene dianion is the strongest superbase and has a proton affinity of 1,843.987 kJ/mol (440.723 kcal/mol).[1] The meta isomer is the second-strongest, and the para isomer is the third.

Isomers[]

Diethynylbenzene dianion isomers
Names
Common name ortho-Diethynylbenzene dianion meta-Diethynylbenzene dianion para-Diethynylbenzene dianion
Identifiers
3D model (JSmol)
 Interactive image Interactive image Interactive image
InChI
 
  • InChI=1S/C10H4/c1-3-9-5-7-10(4-2)8-6-9/h5-8H/q-2
    Key: GGQMWKMAMDPRPA-UHFFFAOYSA-N
SMILES
 
  • [C-]#Cc0ccccc0C#[C-]
 
  • 1=[C-]#Cc0cccc(c0)C#[C-]
 
  • 1=[C-]#Cc1ccc(cc1)C#[C-]
Properties
Molecular formula C10H42–
Molar mass 124.142 g·mol−1

See also[]

References[]

  1. ^ a b c Poad, Berwyck L. J.; Reed, Nicholas D.; Hansen, Christopher S.; Trevitt, Adam J.; Blanksby, Stephen J.; Mackay, Emily G.; Sherburn, Michael S.; Chan, Bun; Radom, Leo (12 January 2018). "Preparation of an ion with the highest calculated proton affinity: ortho-diethynylbenzene dianion". Chemical Science. 7 (9): 6245–6250. doi:10.1039/C6SC01726F. PMC 6024202. PMID 30034765.
  2. ^ Bergius, Will (19 July 2016). "Basically record breaking". Chemistry World.
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