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Resonance formic acid

Experiments were performed at 5°C in order to arrest the cis-trans isomerization of the protonated Schiff base. Spectra with one equivalent of acid and different mixing times showed one NOE cross-peak between H15 of the retinal molecule and the proton on the counterion, as shown for a mixing time of 0.4 s in Figure 10. The strong chemical shift dependence of the H15 resonance on the concentration of the acid dictated the use of less than one equivalent of the protonating formic acid, and therefore an incomplete protonation (>80%) of the retinal, in order to avoid an overlap between the formate and the H15 peaks in the spectrum. This should not affect the observed result since an average chemical shift, between those of HI 5 of the retinal in its nonprotonated and protonated... [Pg.91]

Thermal decomposition of allylbenzene ozonide (58) at 37°C in the liquid phase gave toluene, bibenzyl, phenylacetaldehyde, formic acid, (benzyloxymethyl)formate, and benzyl formate as products. In chlorinated solvents, benzyl chloride is also formed and in the presence of a radical quench such as 1-butanethiol, the product distribution changes. Electron spin resonance (ESR) signals are observed in the presence of spin traps, adding to the evidence that suggests radicals are involved in the decomposition mechanism (Scheme 9) <89JA5839>. [Pg.596]

Formic acid irradiation of, 3 183 reaction with hydrogen atom, 3 191 Formylium cation, 9 231 Formylmethanofuran dehydrogenase, Methano-bacterium wolfei, 40 73 Fossil fuel, radiocarbon and, 3 311-312 Four-coordinated metal centers, 37 19 Fourier-transform infrared spectroscopy, NiFe hydrogenase, 47 295-298, 299, 303 Fourier-transform ion cyclotron resonance... [Pg.110]

In. a number of cases sub-maxima associated with vXH bands have been interpreted in this fashion and in the case of the carboxylic acid dimers this question has been investigated in some detail [4]. A prominent satellite band accompanying the main vOH bands has been assigned to an overtone of the <5QH vibration, and it has been possible to explain formally most of the multiplicity of peaks in the rOH band of formic acid in Fermi resonance terms. Although it is possible that some of these peaks correspond to Stepanov-type sub-bands, no convincing series of this type can be picked out. There seems little doubt that in many cases a considerable number of sub-bands in the rXH region are to be interpreted in terms of Fermi resonance [5, 43,... [Pg.96]

Reaction 11 involves hydrogen atom transfer as proposed by Halpern et al. (13) in the mechanism of formic acid oxidation by cobalt (III) in aqueous solutions. In this reaction one could consider that as peracetic acid approaches the coordination sphere of Co111 and transfers the hydrogen atom to the coordinated acetate, the Co111 atom is transformed into a Co11 complex of peracetoxy radical (or Co111 complex of peracetate anion). Complexes of free radicals with metal ions have been postulated by Kochi (16). The substitution rate in this complex could be intermediate between the rate of substitution of cobalt (III) and cobalt (II) complexes owing to the contribution of the resonance structures ... [Pg.376]

Formic acid. The mix depicted in Eq. 2 was transferred into 1+5 (v/v) formic acid, incubated for 20 minutes and the solvents were evaporated in vacuo. The 31p NMR spectrum was recorded at pH 8.10. All R-l-P had been hydrolyzed and resonances corresponding to pl Oh and were observed, indicating C-0 cleavage. [Pg.589]

Figure 9.31. FIR laser magnetic resonance spectrum of CO in the a 3n state, observed using the 393.6 pm line from formic acid [62]. This spectrum arises from the J = 7 — 6 rotational transition in the Q = 2 fine-structure state, and the transitions obey the selection rule A Mj = +1. The lower Mj states are indicated in the diagram. Figure 9.31. FIR laser magnetic resonance spectrum of CO in the a 3n state, observed using the 393.6 pm line from formic acid [62]. This spectrum arises from the J = 7 — 6 rotational transition in the Q = 2 fine-structure state, and the transitions obey the selection rule A Mj = +1. The lower Mj states are indicated in the diagram.
Because of the high precision with which the frequencies of the interstellar lines can be measured (better than 1 part in 10s) there remains usually little doubt about the positive identification of the molecular species, despite the fact that only a few transitions out of the whole rotational spectrum of any one given molecule have been observed to date in the radio frequency range. Confirmation is obtained from observations of other rotational transitions, or from the detection of possible fine-structure components, or from observations of corresponding transitions of isotopically substituted species. However, some uncertainty still remains in the identification of formic acid, HCOOH, whose 1 io-ln transition is located in between two 18OH resonances. An independent search for the l0i — 0Oo transition for formic acid was negative (Snyder and Buhl, 1972). Similarly the identification of H2S and H20 still rests on only one observed interstellar radio transition and awaits further confirmation by the detection of other transitions. [Pg.39]

Effect of nonaqueous solvents on acid-base properties of NGu) (Acidic in dimethyl-formamide, pyridine and acet basic in HAc and formic acid) 26) E. Ripper, Explosivst 17 (7), 145-51 (1969) Bt CA 72, 48454(1970) (a-and /3-Nitroguanidine) (Reinvestigation of both forms by IR UV, Nuclear Magnetic Resonance (NMR), Differential Thermal Analysis (DTA),... [Pg.800]

Table 3.9. A plot of the difference in these DPEs with n is linear, and extrapolating back to n = 0 gives a valne of 13.5 kcal mor. This is an estimate of the resonance energy contribution to the acidity enhancement of formic acid. Table 3.9. A plot of the difference in these DPEs with n is linear, and extrapolating back to n = 0 gives a valne of 13.5 kcal mor. This is an estimate of the resonance energy contribution to the acidity enhancement of formic acid.
Holt, J. Karty, J. M. Origin of the acidity enhancement of formic acid over methanol resonance versus inductive effects, J. Am. Chem. Soc. 2003,125, 2797-2803. [Pg.183]

Winkler, A., Mehl, J. B., and Hess, P, Chemical relaxation ofH bonds in formic acid vapor studied by resonant photoacoustic spectroscopy, J. Chem. Phys. 100, 2717-2727 (1994). [Pg.45]

From computations with basis sets of the polarized 6-3IG type, at SCF and MP2 levels, the change from formic acid dimer to acetic acid dimer has only a very minor influence upon the energetics of binding . This conclusion is indeed verified by resonant laser photoacoustic spectroscopic measurements i 79,181,182 which find further that trifluoroacetic and propionic acid dimers have a very similar binding enthalpy to formic dimer. One may extrapolate that the formic acid dimer Fl-bond energy is probably applicable for most carboxylic acids with alkyl chains replacing the CH group. [Pg.101]

Wiberg, K. B., and Laidig, K. E., Barriers to rotation adjacent to double bonds. 3. The C—O barrier in formic acid, methyl formate, acetic acid, and methyl acetate. The origin of ester and amide resonance", J. Am. Chem. Soc. 109, 5935-5943 (1987). [Pg.359]


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See also in sourсe #XX -- [ Pg.794 ]

See also in sourсe #XX -- [ Pg.794 ]

See also in sourсe #XX -- [ Pg.794 ]

See also in sourсe #XX -- [ Pg.739 ]

See also in sourсe #XX -- [ Pg.739 ]




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