Paring mechanism

Figure 13.53 Paring mechanism for making ethylene from hexamethylbenzene during MTO.

With ethyl- or isopropylmethyl benzenes expansion to a seven-membered ring intermediate, followed by contraction has also been suggested as a possible route for enabling the paring mechanism [118]. 

Scheme 8.14 The paring mechanism, by which polymethylated aromatics give alkenes.

The paring mechanism ( stands for C). Adapted from Olsbye (J, Bjorgen M, Svelle S, Lillerud K-P, Kolboe S. Mechanistic insight into the methanoi-to-hydrocarbons reaction. Catai Today 2005 106 108— 11. 

Wang C-M, Wang Y-D, Liu H-X, Xie Z-K, Liu Z-P. Theoretical insight into the minor role of paring mechanism in the methanol-to-olefins conversion within HSAPO-34 catalyst. Microporous Mesoporous Mater 2012 158 264-71. 

Molecular mechanics strain energies have another use They can also be used to com pare the energies of models that share the same molecular formula that is models that are either stereoisomers or different conformations of a single molecule (allowed com parisons are shown here)... 

Klotz and associates120 found that PEI-D-Im-type models catalyzed hydrolyses of 4-nitrocatechol sulfate by a two step mechanism resembling that of a natural enzyme. The polymer was reported to accelerate the rate by a factor of 1012 arm-pared to imidazole itself, and of 102 compared to a type-11A arylsulfatase enzyme. 

Tab. 11.2 Mechanical properties of spider si materials. Ik from Nephila davipes com pared to other structural...

Quotation from Sommerfeld, Atomic Structures, 79. On p. vi, Sommerfeld notes that in the chapter on the natural system of the elements, "the former discussions of molecular models and atomic volumes have been thoroughly pared down." At Harvard in 1925, Edwin Kemble s course in quantum mechanics included the second edition of Sommerfeld s Aufbau, according to Schweber (1990 348). Similarly, Joseph Hirschfelder was reading it as an undergraduate at Yale according to Hirschfelder, "My Adventures in Theoretical Chemistry," Ann.Rev.P.Chem. 33 (1983) 129, on 4. 

James A, Pare P, Hogg J The mechanics of airway narrowing in asthma. Am Rev Respir Dis 1989 139 242-246. 

Fig. 9 Schematic band diagram depicting the mechanism by which a semiconductive polymer can produce an enhancement in PArE 34. (Reprinted with permission from Ref. [30]. Copyright 2003 Wiley-VCH Verlag GmbH)...

This rather unspecific induction of nectar secretion in cotton was surprising in light of the fact that the induction of volatile emission by this plant had been demonstrated to be specific. Herbivore-damaged plants show a higher rate of volatile emission compared with mechanically damaged plants (McCall et al, 1994), and herbivore feeding induced de novo synthesis of various terpenoids (Pare and Tumlinson, 1997), which resulted in a quantitative as well as a qualitative response to herbivory. The specificity of the plant response is not restricted to the differentiation between mechanical damage and herbivory. The composition of the induced volatile blend also varies between (even closely related) herbivore species (De Moraes etal, 1998). 

Pyra/olincs and oxazolincs (339, Ing. 132 see also 262 in Sec. B.2) are pre-pared - - by the well-known reaction with hydrazines and hydroxylamines, respectively. Investigations carried out with isotopes allow the exclusion of an elimination-addition mechanism for the reaction, at least in the case of the oxaz.olinc synthesis. ... 

Choline, a component of the phospholipids in cell membranes, can be pre pared by S>j2 reaction of trimelhylamine with ethylene oxide. Show the struc ture of choline, and propose a mechanism for the reaction. 

The first three nucleophiles react at the same rate within experimental error while the last two are clearly faster. The first three nucleophiles react at the same rate because they react by the SnI mechanism whose rate does not depend on the nucleophile. All the nucleophiles in fact react by SnI at the same rate (about 4.0x10 s h but good nucleophiles also react bySN2. The Sn2 rate for hydroxide is about 70 and for PhS about 107. Com pare these relative rates with those in Table 17.6 for reactions with MeBr where they all react at different rates by the Sn2 reaction. 

Figure 5. Layered Mg2(Si,Ge,Sn) ingot pre- Figure 6. Hall mobility of two mechanically pared by hot pressing. alloyed, hot pressed Mg2Si samples.

For large biomolecules in which the conformations are numerous and only a few are chemically important, molecular mechanics, molecular dynamics, or other non-QM methods are good for paring down the possibilities. 

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