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Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values

Robert Vianello   ORCID icon orcid.org/0000-0003-1779-4524 ; Quantum Organic Chemistry Group, Department of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička cesta 54, POB 180, 10002 Zagreb, Croatia

Puni tekst: engleski, pdf (2 MB) str. 27-39 preuzimanja: 1.393* citiraj
APA 6th Edition
Vianello, R. (2009). Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values. Croatica Chemica Acta, 82 (1), 27-39. Preuzeto s https://hrcak.srce.hr/37976
MLA 8th Edition
Vianello, Robert. "Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values." Croatica Chemica Acta, vol. 82, br. 1, 2009, str. 27-39. https://hrcak.srce.hr/37976. Citirano 15.05.2021.
Chicago 17th Edition
Vianello, Robert. "Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values." Croatica Chemica Acta 82, br. 1 (2009): 27-39. https://hrcak.srce.hr/37976
Harvard
Vianello, R. (2009). 'Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values', Croatica Chemica Acta, 82(1), str. 27-39. Preuzeto s: https://hrcak.srce.hr/37976 (Datum pristupa: 15.05.2021.)
Vancouver
Vianello R. Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values. Croatica Chemica Acta [Internet]. 2009 [pristupljeno 15.05.2021.];82(1):27-39. Dostupno na: https://hrcak.srce.hr/37976
IEEE
R. Vianello, "Acidifying Effect of an N-Oxide Group – A Useful Motif in Enhancing Acidity towards Superacidic Values", Croatica Chemica Acta, vol.82, br. 1, str. 27-39, 2009. [Online]. Dostupno na: https://hrcak.srce.hr/37976. [Citirano: 15.05.2021.]

Sažetak
DFT calculations carried out on trans-decahydronaphthalene and 4b,8b-dihydronaphthalene, important structural features of many alkaloids, revealed that they are moderately acidic carbon acids in
the gas-phase and in DMSO solution. Substitution with a nitrogen atom of a neighbouring C(sp3)–H fragment bonded to an acidic centre reduces the corresponding acidity in both phases. Following that, oxidation of the nitrogen atom to an N–oxide group enhances the acidity significantly. This acidifying effect of an N–oxide moiety in the vicinity of a deprotonation centre was estimated to be around 9−17 kcal mol-1 in the gas-phase deprotonation enthalpy and about 5−11 pKa units in DMSO. Therefore, this electronic effect could be applied in the design of novel strong acids and superacids. Such acidity enhancement is identified through triadic analysis to be a consequence of the final state effect of anion, where compounds bearing an N–oxide group benefit from the favourable charge-dipole interaction between the negative charge and an N–O group. A dramatic increase in acidity is observed upon multiple cyanation. For example, octacyanoquinolizine
N–oxide is an extremely strong superacid as seen by the gas-phase ΔHacid = 254.8 kcal mol-1 and pKa,DMSO = −20.2, and its synthesis is highly desirable and strongly recommended. Triadic analysis suggests that this huge acidifying effect takes place because of strong resonance in anions of polycyano compounds, efficiently assisted by multiple CN groups, which stabilizes the corresponding principal molecular orbitals.

Ključne riječi
triadic analysis; deprotonation; isodensity polarized continuum model; pKa value; superacids

Hrčak ID: 37976

URI
https://hrcak.srce.hr/37976

Posjeta: 1.839 *