Bonds selection

Crim F F 1996 Bond-selected chemistry vibrational state control of photodissociation and bimolecular reaction J. Phys. Chem. 100 12 725-34... 

Figure B2.5.18 compares this inter molecular selectivity with intra molecular or mode selectivity. In an IR plus UV, two-photon process, it is possible to break either of the two bonds selectively in the same ITOD molecule. Depending on whether the OFI or the OD stretching vibration is excited, the products are either IT -t OD or FIO + D [24]- hr large molecules, mirmnolecular selectivity competes with fast miramolecular (i.e. unimolecular) vibrational energy redistribution (IVR) processes, which destroy the selectivity. In laser experiments with D-difluorobutane [82], it was estimated that, in spite of frequency selective excitation of the...

Compute (LVIMX. Search on bonds. Setup bonds, select all and hit OK. Enter Job Name 1-butene and Run (Jininx. Yon will see the model being kicked" repeatedly, l.eft click outside of the GMMX Hun box. You should see 3 minimized and 3 found. We already know that there are only three con formers, two of which are degenerate hetice, because E un nuirn we know all the... 

Metal hydrides reduce preferably polar double bonds, whereas catalytic hydrogenation is somewhat selective for non-polar double bonds. Selective protection of amino groups in amino acids. 

The A -double bond is readily hydrogenated selectively in the presence of a A -doiible bond. With other double bonds selectivity is not so easily achieved. ... 

The thermodynamic analysis of the selectivity of ion exchange with the participation of ions of quaternary ammonium bases [56--58] has shown that an increase in bonding selectivity, when metal ions are replaced by organic ions, which is usually accompanied by an increase in entropy of the system (Table 5). It follows from Table 5 that a drastic increase in bonding selectivity upon passing to a triethylbenzylammonium counterion (the most complex ion) is due to a considerable increase in the entropy of the system. 

In many of these processes, organisms break chemical bonds selectively without resorting to high temperature. 

The present excitation scheme of quadratic chirping can be applied to higher dimensional systems easily. As an example, we consider the bond-selective... 

Polyatomic molecules provide a still richer environment for studying phase control, where coupling between different dissociation channels can occur. Indeed, one of the original motivations for studying coherent control was to develop a means for bond-selective chemistry [25]. The first example of bond-selective two-pathway interference is the dissociation of dimethyl-sulfide to yield either H or CH3 fragments [74]. The peak in Fig. 11 is indicative of a resonance embedded in an elastic continuum (case 4). 

Ben-Nun M, Molnar F, Schulten K, Martinez TJ (2000) The role of intersection topography in bond selectivity of cis-trans photoisomerization. Proc Natl Acad Sci USA 97 9379... 

Figure 14 Structure of the [TejSe ] anion in Cs2Te2Se6S4 with long Te. .. Se interactions (> 291 pm) depicted as open bonds. Selected bond lengths Tel-SelA 292.2(2), Tel-Se2 260.3(1), Tel-Se3 271.8(2), Tel-SelB 324.4(1) pm...

Scheme 16.4S Influence ofthe substituents on the Jt-bond selectivity.

A tandem hydroformylation/carbonyl ene reaction can be observed in cases, in which substrates with at least two isolated oleftnic bonds are hydro-formylated at only one double bond selectively. Thus hydroformylation of limonene with PtCkCPPlH /SnCk/PPlH or PtCl2(diphosphine)/SnCl2/PPh3 gives a mixture of two diastereomeric alcohols upon carbonyl ene reaction of the intermediate aldehyde, (Scheme 36). Best results are achieved with a PtC Cdppb) complex. The mechanism of the final intramolecular cycli-zation step resembles an acid catalyzed carbonyl ene reaction [89]. 

Sinha, A. Hsiao, M. C., and Crim, F. F. (1991), Controlling Bimolecular Reactions Mode and Bond Selected Reaction of Water with Hydrogen Atoms, J. Chem. Phys. 94, 4928. 

The same "heuristic principles" which are applied to carbocyclic compounds also hold true for simple heterocyclic compounds containing one heteroatom. However, in the case of bridged heterocyclic molecules a modified strategic bond selection must be applied. Besides the strategic bonds which meet Corey s six rules, the bonds directly attached to nucleophilic heteroatoms -such as O, S and N-are also strategic Cf. heuristic principle HP-7), provided that they satisfy rules 2B, 4, 5 and 6. For instance, in compound 31a besides the five strategic bonds determined by rules 1-6 (cf. compound 26), the sixth darkened C-N bond in 31b is also a strategic bond. 

As an example of strategic bond selection let us consider the polycyclic network of patchouli alcohol (which is, in fact, a homoisotwistane) and see how a feasible synthetic route to its nor-derivative could acmally be performed. 

From a purely systematic point of view, it is convenient to present the results of strategic bond selection by means of a double entry table (see Table 7.1). 

After introducing the algorithm for strategic bond selection developed in connection with "computer-assisted synthetic analysis" (see Part B), we can now return to the use of radical intermediates in the synthesis of monocyclic (and polycyclic) compounds (see Heading 6.1.3). 

Simple alkenes such as 1-octene are completely resistant to this cation-radical hydrogenation. This makes it possible to reduce a more ionizable double bond selectively in the presence of a simple alkene moiety as illustrated for l,l-bis(anisyl)hexa-l,5-diene in Scheme hexa-1,5,7.5 (Mirafzal et al. 1993). 

Triphenylstannane reduced the double bond in dehydro-)J-ionone in 84% yield [872], Complex copper hydrides prepared in situ from lithium aluminum hydride and cuprous iodide in tetrahydrofuran at 0° [873], or from lithium trimethoxyaluminum hydride or sodium bis(methoxy-ethoxy)aluminum hydride and cuprous bromide [874] in tetrahydrofuran at 0° reduced the a,p double bonds selectively in yields from 40 to 100%. Similar selectivity was found with a complex sodium bis(iron tetracarbonyl)hydride NaHFe2(CO)g [875]. 

OYAMA ET AL. Adsorbate Bonding Selectivity in Partial Oxidation... 

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