Stepwise processes

A) During the luultiphoton excitation of molecular vibrations witli IR lasers, many (typically 10-50) photons are absorbed in a quasi-resonant stepwise process until the absorbed energy is suflFicient to initiate a unimolecular reaction, dissociation, or isomerization, usually in the electronic ground state. 

B) The multiphoton excitation of electronic levels of atoms and molecules with visible or UV radiation generally leads to ionization. The mechanism is generally a combination of direct, Goeppert-Mayer, and quasi-resonant stepwise processes. Since ionization often requires only two or tln-ee photons, this type of multiphoton excitation is used for spectroscopic purposes in combination with mass-spectrometric detection of ions. 

This is a stepwise process in which chloramine [10599-90-3] is first formed from ammonia and hypochlorite in a rapid reaction at low temperature ... 

Fatty Acid Neutralization. Another approach to produce soap is through the neutralization of fatty acids with caustic. This approach requires a stepwise process where fatty acids are produced through the hydrolysis of fats and oils by water, followed by subsequent neutralization with appropriate caustics. This approach has a number of inherent benefits over the saponification process. 

Isonitriles and some nitriles can be viewed formally as having a nucleophihc center and an electrophilic center at the same skeleton atom Tnmethylsilylcyanide and cyanoformates add to hetero-1,3 dienes in a stepwise process to give five-mem bered rmg systems with the same stmcture as the isonitnle adducts [41],... 

Five-membered ring systems are also formed on transfer of single-skeletona-tom fragments, usually in a stepwise process CR2 from diazo alkanes [28], NH from azourude (hydrazoic acid) [134], O from peroxy acids [/ii], S from phos-... 

To establish the transfer units draw in line A-fi-C so that it is always half-way vertically between the equilibrium line and the operating line, making dimension 1-2 eqtxal to 2-3. fiegin drawing the transfer units at the overhead product 4, such that 4-9 equals 9-5, then drop vertically to the operating line and repeat the process always making the line A-fi-C bisect the horizontal portion of the step. At the feed point re-start the stepwise process if the transfer unit step does not terminate at the feed point 7. 

The thermal addition of dimethyl acetylenedicarboxylate to indoles, unlike the photocycloaddition (see Section 3.2.1.4.1.1.), proceeds via a polar stepwise process to yield, initially, 3,4-benzo-2-azabicyclo[3.2.0]hepta-3,6-dienes which in some cases are isolable,13 141 but which, in general, ring open in situ to give the indolylacrylates 3 and/or undergo electrocyclic ring expansion to 1-benzazepines.21... 

For the cyclotrimerization of alkynes, several mechanisms have been proposed. The most plausible ones are a concerted fusion of three ir-bonded alkyne molecules, and stepwise processes involving a cyclobutadiene complex or a five-membered metallocyclic intermediate (98). In the case of the cyclotrimerization of a-alkynes it is possible to discriminate between a reaction pathway via a cyclobutadiene complex and the other reaction pathways, by analysis of the products. If cyclotrimerization proceeds via a cyclobutadiene complex and if steric factors do not affect the reaction,... 

In the case of the 2,1-naphthoquinone diazide Zeller (1975a) was able to demonstrate clearly that the electron impact induced loss of N2, CO, and H is a stepwise process. The question of the possible involvement of a naphthooxirene intermediate (4.25) was clearly answered by mass spectrometry of the l-13C-2,1-naphthoquinone diazide (4.24). The [M - N2 - CO]+ radical ion (4.26) does not contain 13C, and therefore no naphthooxirene is formed (Scheme 4-4). 

Phenylsulphine prepared in situ from phenylmethanesulphinyl chloride and triethyl-amine reacted with 1 -morpholinocyclohexene to form the addition product 169 having the enamine structure218. A similar experiment with phenylsulphine and 2-pyrrolidinocyclo-hexene gave only 2-phenylmethanesulphinyl cyclohexanone 170. The latter is most probably formed by hydrolysis of the corresponding enamine sulphoxide upon isolation. The reaction of sulphines with enamines is apparently a stepwise process involving the transient formation of the dipolar intermediate 171 which is stabilized by proton transfer, giving the enamine sulphoxide. 

For benzoyl and acetyl peroxides, loss of carbon dioxide occurs in a stepwise process. Estimates of the rate constants for step c in Scheme 1 are 7 x 10 sec (benzene, 60°). The corresponding process for acetyl peroxide has k = 2x 10 sec (n-hexane, 60°), so that the lifetime of radical pairs containing acetoxy radicals is comparable to the time necessary for nuclear polarization to take place (Kaptein, 1971b Kaptein and den Hollander, 1972 Kaptein et al., 1972). Propionoxy radicals are claimed to decarboxylate 15-20 times faster than acetoxy radicals (Dombchik, 1969). 

Numerous oxidation reactions of sulfur compounds have been described in which S2O or its precursor SO are formed as intermediates but most of these reactions are not suitable to investigate the properties of S2O because of the low yield or the interference from by-products [1]. A relatively clean process is the reaction of oxygen atoms with COS producing SO and CO. The formation of S2O from gaseous SO is a stepwise process according to the following equations (M is a collision partner) [21] ... 

The reformation, or formation, of molecules appears to be a stepwise process—that is, it occurs by sequential reactions which may by interrupted at certain stages ... 

The quantity of AsPha fixed and Ce evolved after 3 h of reaction at 303,373, and 443 K, related to the amount of total Ni (As xed/Nit) or to the number of surface atoms (Asfixed/Nis) as reported in Table 6 indicates that the reaction of AsPha with Ni under H2 proceeds through a stepwise process, with a progressive hydrogenolysis of the As - Ph bonds. Moreover, after reaction at 443 K, the diffraction pattern of the sohd presents clear lines at 33.6 and 50.5 26 assigned to the NiAs phase (nickeUne), thus showing that an alloy has been formed. 

The mechanism for catalysis is formulated as a stepwise process in which the electrophilic character of Pd(II) facilitates the bond formation.209... 

Figure 3. Solution polymerization with BCl. Stepwise process.

We have seen that the observation of mixed radical combination products from mixtures of 2CHCOCH< 2 and CH2COCH2 upon photolysis indicates the decarbonylation to be stepwise rather than concerted, at least for these molecules. Further evidence in support of a stepwise process was reported by Robbins and Eastman in a study of p-methoxybenzyl ketone/64 Three products are isolated from this reaction ... 

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