Elimination orientation

Electron spin resonance (ESR), nuclear magnetic resonance (NMR) and, 50-51 eliminateOrt. See Orientation Elimination program (eliminateOrt)... 

FIGURE 3-9. Installation of Pump Suction Reducers. (a,b) Concentric reducer can allow formation of pocket of undissolved gases when pump is shot off. This produces cavitation at startup. This reducer also can allow sedimentation of hazardous solids in the line during shutdown. (c,d) Installation of eccentric reducer in this orientation eliminates gas pockets. (e,f) This orientation prevents sedimentation. 

A brief account of aromatic substitution may be usefully given here as it will assist the student in predicting the orientation of disubstituted benzene derivatives produced in the different substitution reactions. For the nitration of nitrobenzene the substance must be heated with a mixture of fuming nitric acid and concentrated sulphuric acid the product is largely ni-dinitrobenzene (about 90 per cent.), accompanied by a little o-dinitrobenzene (about 5 per cent.) which is eliminated in the recrystallisation process. On the other hand phenol can be easily nitrated with dilute nitric acid to yield a mixture of ortho and para nitrophenols. It may be said, therefore, that orientation is meta with the... 

Based on the above-mentioned stereochemistry of the allylation reactions, nucleophiles have been classified into Nu (overall retention group) and Nu (overall inversion group) by the following experiments with the cyclic exo- and ent/n-acetales 12 and 13[25], No Pd-catalyzed reaction takes place with the exo-allylic acetate 12, because attack of Pd(0) from the rear side to form Tr-allyl-palladium is sterically difficult. On the other hand, smooth 7r-allylpalladium complex formation should take place with the endo-sWyWc acetate 13. The Nu -type nucleophiles must attack the 7r-allylic ligand from the endo side 14, namely tram to the exo-oriented Pd, but this is difficult. On the other hand, the attack of the Nu -type nucleophiles is directed to the Pd. and subsequent reductive elimination affords the exo products 15. Thus the allylation reaction of 13 takes place with the Nu nucleophiles (PhZnCl, formate, indenide anion) and no reaction with Nu nucleophiles (malonate. secondary amines, LiP(S)Ph2, cyclopentadienide anion). 

Axial halide is in proper orientation for anti elimination with respect to axial hydrogens on adjacent carbon atoms Dehydrobromination is rapid... 

Prior to solvation, the solute is oriented according to its inertial axes such that the box size needed to accommodate it is minimized (minimizing the number of water molecules). The principal inertial axis is oriented along the viewer s Z axis, for example. Then water molecules are eliminated if any of the three atoms are closer to a solute atom than the contact distance you specify. 

Terephthahc acid (TA) or dimethyl terephthalate [120-61 -6] (DMT) reacts with ethyleae glycol (2G) to form bis(2-hydroxyethyl) terephthalate [959-26-2] (BHET) which is coadeasatioa polymerized to PET with the elimination of 2G. Moltea polymer is extmded through a die (spinneret) forming filaments that are solidified by air cooling. Combinations of stress, strain, and thermal treatments are appHed to the filaments to orient and crystallize the molecular chains. These steps develop the fiber properties required for specific uses. The two general physical forms of PET fibers are continuous filament and cut staple. 

Baffles in a horizontal in-shell condenser are oriented with the cuts vertical to facilitate drainage and eliminate the possibility of flooding in the upward cross-flow sections. Pressure drop on the vapor side can be estimated by the data and method of Diehl and Unruh [Pet. Refiner, 36(10), 147 (1957) 37(10), 124 (1958)]. 

Different manufacturers have adopted different methods with minor changes to achieve almost the same objective. For example, field-oriented control was first introduced by Allen Bradley in the USA in 1981 and a similar technique was introduced at the same time by ABB of Finland. ABB claim their technique to be still faster in responding, as it eliminates the modulation section of... 

SIMS, and SNMS in rare cases, such as for HgCdJTei samples or some polymers, the sample structure can be modified by the incident ion beam. These effects can often be eliminated or minimized by limitii the total number of particles incident on the sample, increasing the analytical area, or by cooling the sample. Also, if channeling of the ion beam occurs in a crystal sample, this must be included in the data analysis or serious inaccuracies can result. To avoid unwanted channelii, samples are often manipulated during the analysis to present an average or random crystal orientation. 

Enby 6 is an example of a stereospecific elimination reaction of an alkyl halide in which the transition state requires die proton and bromide ion that are lost to be in an anti orientation with respect to each odier. The diastereomeric threo- and e/ytAra-l-bromo-1,2-diphenyl-propanes undergo )3-elimination to produce stereoisomeric products. Enby 7 is an example of a pyrolytic elimination requiring a syn orientation of die proton that is removed and the nitrogen atom of the amine oxide group. The elimination proceeds through a cyclic transition state in which the proton is transferred to die oxygen of die amine oxide group. 

We have previously seen (Scheme 2.9, enby 6), that the dehydrohalogenation of alkyl halides is a stereospecific reaction involving an anti orientation of the proton and the halide leaving group in the transition state. The elimination reaction is also moderately stereoselective (Scheme 2.10, enby 1) in the sense that the more stable of the two alkene isomers is formed preferentially. Both isomers are formed by anti elimination processes, but these processes involve stereochemically distinct hydrogens. Base-catalyzed elimination of 2-iodobutane affords three times as much -2-butene as Z-2-butene. 

Table 6.S. Orientation in E2 Elimination as a Function of Base Strength...

Table 6.6. Orientation of Elimination in the 2-Butyl System under Various E2 Conditions...

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