Formaldehyde unimolecular reactions

Polik W F, Guyer D R, Miller W H and Moore C B 1990 Eigenstate-resolved unimolecular reaction dynamics ergodic character of Sq formaldehyde at the dissociation threshold J. Chem. Phys. 92 3471-84... 

J. Troe, Theory of multichannel thermal unimolecular reactions. 2. Application to the thermal dissociation of formaldehyde, /. Phys. Chem. A109 (37) (2(X)5) 8320-8328. 

Dissociation of formaldehyde, CHgO, at comparably low temperatures is obviously determined by a complex decomposition mechanism. Conclusions on the unimolecular dissociation can only be drawn from measurements at high temperatures under shock wave conditions. In this system the primary dissociation leading to formyl radicals is followed by decomposition of CHO and subsequent reactions of H atoms with CH2O and CHO. By analysing the chain mechanism the rate constant of the unimolecular reaction was derived. ... 

G levels. The results suggest that a concerted and asynchronous four-membered cyclic TS applies for each of the two parallel unimolecular reactions occurring to give either isobutene and formaldehyde or ethene and acetone, respectively. 

In the area of reaction energetics. Baker, Muir, and Andzehn have compared six levels of theory for the enthalpies of forward activation and reaction for 12 organic reactions the unimolecular rearrangements vinyl alcohol -> acetaldehyde, cyclobutene -> s-trans butadiene, s-cis butadiene s-trans butadiene, and cyclopropyl radical allyl radical the unimolecular decompositions tetrazine -> 2HCN -F N2 and trifluoromethanol -> carbonyl difluoride -F HF the bimolecular condensation reactions butadiene -F ethylene -> cyclohexene (the Diels-Alder reaction), methyl radical -F ethylene -> propyl radical, and methyl radical -F formaldehyde -> ethoxyl radical and the bimolecular exchange reactions FO -F H2 FOH -F H, HO -F H2 H2O -F H, and H -F acetylene H2 -F HC2. Their results are summarized in Table 8.3 (Reaction Set 1). One feature noted by these authors is... 

A unimolecular elimination involving a semi-polar five-membered cyclic transition state (81) (Scheme 9, R1 = Ph, R2 = R3 = H) appears to account for the formation of benzaldehyde, CO, and H2O on eliminative fragmentation of mandelic acid in the gas phase.44 The same type of transition state has been proposed for gas-phase pyrolysis of ROCH2COOH (R = MeO, EtO, and Ph O) with corresponding formation of ROH, CO, and formaldehyde the rate of reaction is little dependent on R.45... 

The complete active space valence bond (CASVB) method is an approach for interpreting complete active space self-consistent field (CASSCF) wave functions by means of valence bond resonance structures built on atom-like localized orbitals. The transformation from CASSCF to CASVB wave functions does not change the variational space, and thus it is done without loss of information on the total energy and wave function. In the present article, some applications of the CASVB method to chemical reactions are reviewed following a brief introduction to this method unimolecular dissociation reaction of formaldehyde, H2CO — H2+CO, and hydrogen exchange reactions, H2+X — H+HX (X=F, Cl, Br, and I). 

In this article, we present applications of CASVB to chemical reactions the unimolecular dissociation reaction of formaldehyde, H2CO — H2+CO [5], and a series of hydrogen exchange reactions, H2+X — H+HX (X-F, Cl, Br, and I). The method in this article is based on the occupation numbers of VB structures that are defined by the weights of the spin-paired functions in the CASVB functions, so that we could obtain a quantitative description of the nature of electronic structures and chemical bonds even during reactions. 

POZ). The reaction enthalpy is retained as the internal energy of the products, resulting in formation of the vibrationally excited ozonide, which subsequently undergoes unimolecular decomposition to yield a chemically activated biradical, known as the carbonyl oxide or Criegee intermediate (Cl), and an aldehyde (e.g., MVK, MACR or formaldehyde). A total of nine carbonyl oxides (methyl vinyl carbonyl oxide, derived from 1,2-ozonide isopropyl carbonyloxide, derived from... 

This ester resembles its methyl homologue in possessing three modes of decomposition [131]. It also supports a self-decomposition flame, the multiple reaction zones of which are clearly separated at low pressures [122, 123, 125]. Temperature and composition profiles in the low-pressure decomposition flame have been measured [133]. The products include formaldehyde, acetaldehyde and ethanol with smaller amounts of methane and nitromethane. The activation energy derived from the variation of flame speed with final flame temperature was 38 kcal. mole", close to the dissociation energy of the RO—NO2 bond. The controlling reaction is believed to be unimolecular in its low pressure regime, and the rate coefficient calculated from the heat-release profile is... 

Transition state barrier height for the unimolecular dissociation reaction of formaldehyde H2CO H2 CO [35]. This reaction is Woodward-Hoffmann... 

In this paper I have not reviewed the various chemical applications that have utilized the reaction path model. These include work in my research group on the unimolecular isomerization of hydrogen isocyanide (HNC HCN), the unimolecular decomposition of formaldehyde (HpCO H2 + CO), the vinylidene-acetylene rearrangement (H2C=C HCsCHT, and hydrogen atom transfer in malonaldehyde,... 

Density functional theory (DPT) calculations have predicted the unimolecular decomposition of P-ISOPO2 radicals (the dominant ISOPO2 isomers), resulting in production of OH, formaldehyde and (depending on the isomer) MVK or MACR [40]. However, the rates of decomposition are expected to be slow, and may not be sufficient to compete effectively with the bimolecular reactions of ISOPO2 radicals with HO2 and NO in all but the most remote enviromnents [40]. 

In addition to Levy s studies referred to above (238, 239), the kinetics of detoxification of staphylococcus toxin by formaldehyde have been studied in some detail (252). The results show that the rate of reaction is directly proportional to the concentration of formaldehyde and to the square root of the hydroxyl ion. The reaction has an unusually high temperature coefScient of 4-5 for a change of 10 C. It is stated that the reaction follows a unimolecular course. This is true only when either the aldehydes or proteins are present in great excess, for the reaction should be bimolecular. Similar results have been obtained with diphtheria... 

U.v. irradiation of formaldehyde on zeolites of types A and X has been shown to produce sugars. A formose reaction carried out in the presence of hydroxyoxo compounds at high pH has been described. Equilibrium constants were evaluated in water and aqueous methanol solution saturated with calcium hydroxide or sodium hydroxide in a unimolecular ratio with formaldehyde and known accelerators, such as 2-hydroxyacetophenone, DL-glyceraldehyde,... 

Let us now briefly consider the alternative /molecular isomerization reaction of formaldehyde to hydroxymethylene (CHOH), whose calculated IRC reaction profile was shown in Fig. 10.3. In this case, NRT analysis of the IRC leads to bond-order variations as plotted in Fig. 10.10, indicating a simple NTS crossing very near the energetic TS saddle-point at Jirc = 0 (quite different from the corresponding Fig. 10.4 for the bimolecular formation reaction). The reaction profile is seen to involve primarily a direct switch between bc i and ion bond orders, with little change of ben and bco bond orders. Accordingly, we anticipate that unimolecular hydroxymethylene isomerization is intrinsically simpler and more direct than... 

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