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Pregled bibliografske jedinice broj: 833714

15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases


Schwamm, Ryan J.; Vianello, Robert; Maršavelski, Aleksandra; García, M. Ángeles; Claramunt, Rosa M.; Alkorta, Ibon; Saame, Jaan; Leito, Ivo; Fitchett, Christopher M.; Edwards, Alison J.; Coles, Martyn P.
15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases // Journal of organic chemistry, 81 (2016), 17; 7612-7625 doi:10.1021/acs.joc.6b01330 (međunarodna recenzija, članak, znanstveni)


CROSBI ID: 833714 Za ispravke kontaktirajte CROSBI podršku putem web obrasca

Naslov
15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases

Autori
Schwamm, Ryan J. ; Vianello, Robert ; Maršavelski, Aleksandra ; García, M. Ángeles ; Claramunt, Rosa M. ; Alkorta, Ibon ; Saame, Jaan ; Leito, Ivo ; Fitchett, Christopher M. ; Edwards, Alison J. ; Coles, Martyn P.

Izvornik
Journal of organic chemistry (0022-3263) 81 (2016), 17; 7612-7625

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
superbase

Sažetak
Pyridine substituted with one and two bicyclic guanidine groups has been studied as a potential source of superbases. 2-{; ; hpp}; ; C5H4N (I) and 2, 6-{; ; hpp}; ; 2C5H3N (II) (hppH = 1, 3, 4, 6, 7, 8-hexahydro-2H-pyrimido[1, 2-a]pyrimidine) were protonated using [HNEt3][BPh4] to afford [I-H][BPh4] (1a), [II-H][BPh4] (2), and [II-H2][BPh4]2 (3). Solution-state 1H and 15N NMR spectroscopy shows a symmetrical cation in 2, indicating a facile proton-exchange process in solution. Solid-state 15N NMR data differentiates between the two groups, indicating a mixed guanidine/guanidinium. X-ray diffraction data are consistent with protonation at the imine nitrogen, confirmed for 1a by single-crystal neutron diffraction. The crystal structure of 1a shows association of two [I-H]+ cations within a cage of [BPh4]− anions. Computational analysis performed in the gas phase and in MeCN solution shows that the free energy barrier to transfer a proton between imino centers in [II-H]+ is 1 order of magnitude lower in MeCN than in the gas phase. The results provide evidence that linking hpp groups with the pyridyl group stabilizes the protonation center, thereby increasing the intrinsic basicity in the gas phase, while the bulk prevents efficient cation solvation, resulting in diminished pKa(MeCN) values. Spectrophotometrically measured pKa values are in excellent agreement with calculated values and confirm that I and II are superbases in solution.

Izvorni jezik
Engleski

Znanstvena područja
Kemija



POVEZANOST RADA


Ustanove:
Institut "Ruđer Bošković", Zagreb

Citiraj ovu publikaciju

Schwamm, Ryan J.; Vianello, Robert; Maršavelski, Aleksandra; García, M. Ángeles; Claramunt, Rosa M.; Alkorta, Ibon; Saame, Jaan; Leito, Ivo; Fitchett, Christopher M.; Edwards, Alison J.; Coles, Martyn P.
15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases // Journal of organic chemistry, 81 (2016), 17; 7612-7625 doi:10.1021/acs.joc.6b01330 (međunarodna recenzija, članak, znanstveni)
Schwamm, R., Vianello, R., Maršavelski, A., García, M., Claramunt, R., Alkorta, I., Saame, J., Leito, I., Fitchett, C., Edwards, A. & Coles, M. (2016) 15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases. Journal of organic chemistry, 81 (17), 7612-7625 doi:10.1021/acs.joc.6b01330.
@article{article, year = {2016}, pages = {7612-7625}, DOI = {10.1021/acs.joc.6b01330}, keywords = {superbase}, journal = {Journal of organic chemistry}, doi = {10.1021/acs.joc.6b01330}, volume = {81}, number = {17}, issn = {0022-3263}, title = {15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases}, keyword = {superbase} }
@article{article, year = {2016}, pages = {7612-7625}, DOI = {10.1021/acs.joc.6b01330}, keywords = {superbase}, journal = {Journal of organic chemistry}, doi = {10.1021/acs.joc.6b01330}, volume = {81}, number = {17}, issn = {0022-3263}, title = {15N NMR Spectroscopy, X-ray and Neutron Diffraction, Quantum-Chemical Calculations, and UV/vis-Spectrophotometric Titrations as Complementary Techniques for the Analysis of Pyridine-Supported Bicyclic Guanidine Superbases}, keyword = {superbase} }

Časopis indeksira:


  • Current Contents Connect (CCC)
  • Web of Science Core Collection (WoSCC)
    • Science Citation Index Expanded (SCI-EXP)
    • Arts & Humanities Citation Index (A&HCI)
    • SCI-EXP, SSCI i/ili A&HCI
  • Scopus


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