Abstract:
Quinones form a large group of organic compounds with various applications in
industry, biological systems, and pharmacology. They can capture an electron
with kinetic energy exceeding zero and keep it for a longer time. The principal
structure responsible for electron capturing in quinones is the para-benzoquinone,
PBQ. Several studies have been carried out on PBQ and its molecular anion, but
less attention has been paid to its derivatives upon capturing an electron. As such,
the focus of this study is to investigate the effects of substituents on the molecular
anion properties of PBQ. These results will fill a void in available data and help
in selecting new compounds as possible candidates for the synthesis of new
electron acceptors. Both theoretical and experimental work were conducted to
obtain the results. Electron donating substituents were found to decrease the
stability of the molecular anion and led to the formation of more anion fragments
under electron capture negative chemical ionisation mass spectrometry (ECNIMS) conditions while electron withdrawing substituents showed the opposite
effect. The theoretical fragmentation schemes constructed for all dissociation
channels in all molecules speculate that most of the fragment anions were formed
due to loss of CO and/or C2H4 from the molecular anions, sometimes accompanied
by migration of H-atom to a nearby or distant C-atom or elimination of H-atom/s.
Electron donating derivatives retained several features of the spectra of PBQ itself.
In addition to the pronounced molecular anion peaks and [M-CO]−
, there were
other significant peaks at m/z 41, 53 ,54, 55, 80 and 81 corresponding to the
formation of [C2HO]−
, [C3HO]−
, [C3H2O]−
, [C3H3O]−
, [C5H4O/ C4O2]
−
and [C4HO2]
−
respectively with electron donating derivatives. Unlike electron donating
derivatives, electron withdrawing derivative’s base peaks were due to the
formation of Cl−
or F−
. The most common fragment anions apart from Cl−
in
chlorinated PBQs at m/z 41, 53 and 80 corresponds to [C2HO]−
, [C3HO]−
, and
[C4O2]
−
, respectively. Density Functional Theory calculations on the electron
affinities, reduction potentials and C=O vibrational frequencies, strongly
supported the observations noticed in ECNI-MS. The destabilizing effect of
electron donating groups decreased the electron affinity, reduction potential and
C=O vibrational frequency of PBQ molecular anion while the stabilizing effect of
electron withdrawing groups increased them. There was a linear correlation
between the response of M−
in ECNCI, electron affinities and reduction potentials.
Nonofo, S (2024). The effect of substituents on the stability and fragmentation of para benzoquinone molecular anion. Afribary. Retrieved from https://afribary.com/works/the-effect-of-substituents-on-the-stability-and-fragmentation-of-para-benzoquinone-molecular-anion
Nonofo, Samuel "The effect of substituents on the stability and fragmentation of para benzoquinone molecular anion" Afribary. Afribary, 30 Mar. 2024, https://afribary.com/works/the-effect-of-substituents-on-the-stability-and-fragmentation-of-para-benzoquinone-molecular-anion. Accessed 15 Oct. 2024.
Nonofo, Samuel . "The effect of substituents on the stability and fragmentation of para benzoquinone molecular anion". Afribary, Afribary, 30 Mar. 2024. Web. 15 Oct. 2024. < https://afribary.com/works/the-effect-of-substituents-on-the-stability-and-fragmentation-of-para-benzoquinone-molecular-anion >.
Nonofo, Samuel . "The effect of substituents on the stability and fragmentation of para benzoquinone molecular anion" Afribary (2024). Accessed October 15, 2024. https://afribary.com/works/the-effect-of-substituents-on-the-stability-and-fragmentation-of-para-benzoquinone-molecular-anion