Intramolecular hydrogen shift in 3--benzyl-6-deoxy--hexofuranosyl-6 radicals and a criterion for determination of the configuration at 1′-position of 6-deoxy-3--(1-phenylalkyl)-1,2--isopropylidene--allofuranoses

Abstract Very recently, a report on the antioxidant activity of flavonoids has appeared, where authors concluded that Hydrogen Atom Transfer mechanism represents the thermodynamically preferred mechanism in polar media (https://doi.org/10.1016/j.foodres.2018.11.018). Unfortunately, serious errors in the theoretical part of the paper led to incorrect conclusions. For six flavonols (galangin, kaempferol, quercetin, morin, myricetin, and fisetin), reaction enthalpies related to three mechanisms of the primary antioxidant action were computed. Based on the obtained results, the role of intramolecular hydrogen bonds (IHB) in the thermodynamics of the antioxidant effect is presented. Calculations and the role of solvation enthalpies of proton and electron in the determination of thermodynamically preferred mechanism is also briefly explained and discussed. The obtained results are in accordance with published works considering the Sequential Proton-Loss Electron-Transfer thermodynamically preferred reaction pathway.

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The atmospheric oxidation of dimethyl, diethyl, and diisopropyl ethers. The role of the intramolecular hydrogen shift in peroxy radicals

Physical Chemistry Chemical Physics ◽

10.1039/c5cp07199b ◽

2016 ◽

Vol 18 (11) ◽

pp. 7707-7714 ◽

Cited By ~ 11

Author(s):

Sainan Wang ◽

Liming Wang

Keyword(s):

Atmospheric Oxidation ◽

Peroxy Radicals ◽

Hydrogen Shift ◽

Intramolecular Hydrogen ◽

Clean Atmosphere

Ethers can be auto-oxidized with no O3 formation in a ‘clean’ atmosphere.

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Dynamic behavior and strategy for the complete 1H and 13C assignments for meso-aryl expanded heptaphyrins

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424602000518 ◽

2002 ◽

Vol 06 (06) ◽

pp. 410-422 ◽

Cited By ~ 2

Author(s):

Bhawani S. Joshi ◽

Venkataramanarao G. Anand ◽

Simi K. Pushpan ◽

Alagar Srinivasan ◽

Tavarekere K. Chandrashekar ◽

...

Keyword(s):

Dynamic Behavior ◽

Intramolecular Hydrogen Bonding ◽

Native State ◽

Temperature Dependent ◽

System A ◽

Expanded Porphyrins ◽

Nmr Techniques ◽

Intramolecular Hydrogen ◽

C Nmr

The detailed 1 H and 13 C NMR analysis of 5,10,19,24-tetramesityl-33,35,36,38,39-pentathiaheptaphyrin (1) and 5,10,19,24-tetraphenyl-35,36-dioxa-33,38,39-trithiaheptaphyrin (2) in the native and protonated state were carried out using two-dimensional NMR techniques. The analysis suggests that the earlier reported structure containing inverted terminal thiophene of trithiophene should be corrected as the inverted thiophene and furan of bithiophene and bifuran instead of trithiophene system of 1 and 2, respectively. Temperature dependent and titration studies suggest that 1 is less flexible in the native state then 2 due to presence of the mesityl group despite having disorder due to the presence of the heavier sulphur atom. This was consequently proven by the NMR information obtained in 5,10,19,24-tetramesityl-35,36-dioxa-33,38,39-trithiaheptaphyrin (3). Whereas in its protonated state, 2 was found to be less flexible than 1 due to presence of intramolecular hydrogen bonding involving N - H --- O between the pyrrole NH and oxygen of the furan of bifuran system. A systematic NMR strategy has been generated in order to provide complete a structure determination of expanded porphyrins along with their dynamic behavior.

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Zusammensetzung von Rohsulfan, Nachweis der Sulfane H2S9 bis H2S35 Composition of Crude Sulfane Oil, Identification of the Sulfanes H2S9 to H2S35

Zeitschrift für Naturforschung B ◽

10.1515/znb-1985-0220 ◽

1985 ◽

Vol 40 (2) ◽

pp. 263-272 ◽

Cited By ~ 21

Author(s):

Josef Hahn

Keyword(s):

Narrow Range ◽

Benzene Solution ◽

Chemical Shifts ◽

Upfield Shift ◽

Downfield Shift ◽

H Nmr ◽

Intramolecular Hydrogen ◽

Hydrogen Bondings ◽

Nmr Signals

In benzene solution the position of the 1H NMR signals of sulfanes, H2Sn, strongly depends on the sulfur chain length and on the sulfane concentration. Under proper conditions all sulfanes in a mixture are characterized by well-resolved NMR signals showing a downfield shift with increasing length of the sulfur chain. The shift differences between the higher homologues ( n > 8 ) remain nearly constant, thus allowing the assignment of the signals up to H2S35 and the determination of the complete sulfane distribution in crude oils. In sulfane mixtures without solvent as well as in CS2 and CCl4 solutions, however, H2S8 shows the largest downfield shift. The signals of the higher sulfanes overlap in a narrow range at slightly higher field and cannot be characterized except for the CCl4 solution where an assignment up to H2S11 is possible. The chemical shifts are interpreted in terms of inter- and intramolecular hydrogen bondings. The upfield shift caused by benzene is attributed to the formation of H2Sn · benzene complexes.

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Synthesis of 2', 6'-Dihydroxychalcones by Using Tetrahydropyran-2-yl and Trialkylsilyl Protective Groups; the Crystal Structure Determination of 2',6'-Dihydroxy-2,4,6-trimethoxychalcone

Australian Journal of Chemistry ◽

10.1071/ch9891103 ◽

1989 ◽

Vol 42 (7) ◽

pp. 1103 ◽

Cited By ~ 13

Author(s):

CO Miles ◽

L Main ◽

BK Nicholson

Keyword(s):

Crystal Structure ◽

Hydrogen Bonding ◽

Intramolecular Hydrogen Bonding ◽

Silyl Ether ◽

X Ray ◽

Protective Groups ◽

Intramolecular Hydrogen ◽

First Time ◽

Mild Acid

Two improved general routes to 2′,6′-dihydroxychalcones are described in which the final step is protective-group removal from O 2′ under mild acid conditions. The first involves base-catalysed condensation of benzaldehydes with 2′-hydroxy-6′-tetrahydropyran-2-yloxyacetophenone, the second ring-opening of 5-hydroxyflavanones with 1,8-diazabicyclo[5.4.0]undec-7-ene in the presence of a trialkylchlorosilane to trap out the chalcone as a bis silyl ether. Chalcones prepared by the first route are 2',6'-dihydroxychalcone (1), and its 4-methoxy (2), 3,4-dimethoxy (3), 3,4,5-trimethoxy (4), and 2,4,6-trimethoxy (5) derivatives. The 4-chloro derivative (6) and the chalcone from hesperetin are prepared by the second method. .The X-ray crystal structure of 2',6'-dihydroxy-2,4,6-trimethoxychalcone (5), the first for a 2',6′-dihydroxychalcone, is reported, the hydrogen involved in intramolecular hydrogen-bonding between the carbonyl and phenolic oxygens being located for the first time for any 2'-hydroxychalcone derivative. The O 6' involved in the intramolecular hydrogen-bonding is also hydrogen-bonded intermolecularly to the hydrogen of the other (2'-)hydroxy group of a neighbouring molecule in the lattice. 13C n.m.r. data are the first reported for a series of 2',6'-dihydroxychalcones.

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