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The conformational analysis of push-pull enaminones using FTIR and NMR spectroscopy, and quantum chemical calculations. VI. β—N—Methyl-aminovinyl trifluoromethyl ketone and α—methyl—β—N—methylaminovinyl trifluoromethyl ketone.
Autorzy
Rok wydania
2017
Czasopismo
Journal of Molecular Structure
Numer woluminu
1128
Strony
741-753
DOI
10.1016/j.molstruc.2016.09.049
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
X-Ray analysis, NMR and IR Fourier spectra of two enaminoketones 4-(N-methylamino)-1,1,1-trifluorobut-3-en-2-one F3Csbnd COsbnd CHdbnd CHsbnd NH(CH3) (1) 4-(N-methylamino)-1,1,1-trifluoro-3-methylbut-3-en-2-one F3Csbnd COsbnd C(CH3)dbnd CHsbnd NH(CH3) (2) were studied in solid state and solutions. It was shown that the substitution of proton at α-position of vinyl moiety with methyl group changes significantly electronic and spatial structure of enaminoketone. In solid state enaminoketone 1 is found to be exclusively as Z-s-Z-ap isomer with intramolecular hydrogen bond. At the same time molecules of enaminoketone 2 have E-s-E-ap stereoisomeric structure forming dimers due to intermolecular Nsbnd HctdotOdbnd C hydrogen bonds. Exposure of Ar-matrix isolated 1 to UV-radiation results in appearance of various E forms with free methylamino- and hydroxy groups. The same effect was observed for 2 in solutions in CCl4 under addition of polar HMPA or DMSO during spontaneous E ⇌ Z isomerization. For enaminoketone 1 under similar conditions we observed
reverse process of Z ⇌ E isomerization, E stereoisomeric forms with hydroxy group being trace quantity only.
Study of solvent influence on FTIR spectra revealed that introduction of methyl group as substituent at α-position of vinyl moiety increases electron population of Cdbnd O double bond. Consequently, in contrast with enaminoketone 1 where the main contribution to the ν˜ (Cdbnd O) band shift to lower wavenumbers in all three stereoisomeric structures makes solvent polarity/polarizability term (π*), influence of solvent's hydrogen bond acceptor (HBA) basicity (β) on ν˜ (Cdbnd O) band shift of 2 predominates in the E-s-Z-ap and Z-s-Z-ap isomers. Similarly to enaminoketone 1, negative shift of the ν˜ (Cdbnd C) band to lower wavenumbers occurs due to hydrogen bond formation between π system of vinyl moiety and hydrogen bond donor solvents in all stereoisomeric forms of enaminoketone 2.
Słowa kluczowe
NMR and IR-spectra, conformational analysis, enaminoketones, density functional calculations
Adres publiczny
http://dx.doi.org/10.1016/j.molstruc.2016.09.049
Strona internetowa wydawcy
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