Electronic effects, fragments

Following a description of femtosecond lasers, the remainder of this chapter concentrates on the nuclear dynamics of molecules exposed to ultrafast laser radiation rather than electronic effects, in order to try to understand how molecules fragment and collide on a femtosecond time scale. Of special interest in molecular physics are the critical, intermediate stages of the overall time evolution, where the rapidly changing forces within ephemeral molecular configurations govern the flow of energy and matter. 

In this contribution, we describe work from our group in the development and application of alternatives that allow the explicit inclusion of environment effects while treating the most relevant part of the system with full quantum mechanics. The first methodology, dubbed MD/QM, was used for the study of the electronic spectrum of prephenate dianion in solution [18] and later coupled to the Effective Fragment Potential (EFP) [19] to the study of the Claisen rearrangement reaction from chorismate to prephenate catalyzed by the chorismate mutase (CM) enzyme [20]. 

In addition to the searchable library compilations, several compendial books on the electron ionization fragmentation behavior of compounds have been published [34-36]. They are dated, but nevertheless effectively capture the collective fragmentation information prior to their publication. All of these information sources discuss electron ionization spectra. El fragmentation rules, however, can be of limited assistance in interpreting soft ionization and MS-MS product ion spectra. 

PtMo alloys are not as effective as PtRu for methanol, or ethanol, oxidation. As shown in Figure 29, the d band vacancy per Pt atom for the PtMo/C catalyst continues to increase until 0.6 V vs RHE, in contrast to the behavior of PtRu/C. ° The authors attribute this difference to the lack of removal of the Cl fragments from the particle surface by the oxy-hydroxides of Mo. However, the difference in the electrocatalytic activity of PtRu and PtMo catalysts may be attributed to ensemble effects as well as electronic effects. The former are not probed in the white line analysis presented by Mukerjee and co-workers. In the case of methanol oxidation, en-... 

An useful alternative to the already known retropinacol reactions is presented by Liu and co-workers [7], This works demonstrates that pinacols bearing (dimethylamino)phenyl substiments can be subjected to fast oxidative fragmentation via photoinduced electron transfer with chloroform as the electron acceptor in yields up to 80%. The extremely fast dechlorination of the chloroform radical anion inhibits back-electron transfer and thus leads to effective fragmentation of the pinacol radical cation (Scheme 8). 

In their first paper, Lepage et al. [37] demonstrated that the appearance of the CO electronic state derives exclusively from the electron-induced fragmentation of condensed methanol molecules. Assuming a uniform electron current density within the electron beam, it can also be shown that for induced CO concentrations below 2%, an effective cross section for CO production Cp can be calculated via the formula... 

The stereoelectronically controlled reaction of hydroxide ion with an 0-labeled tertiary amide(J8 ) (Fig. 3) should give the intermediate 19 which can fragment in only two ways, yielding the starting labeled amide J8 or the hydrolysis products direct cleavage of W to give unlabeled amide 18 cannot take place with the help of the primary electronic effect. In order to form the unlabeled amide J8 with stereoelectronic control, intermediate Jj) must first be converted into another conformer such as 20. Oxygen... 

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