Factors favoring

Economy of time and resources dictate using the smallest sized faciHty possible to assure that projected larger scale performance is within tolerable levels of risk and uncertainty. Minimum sizes of such laboratory and pilot units often are set by operabiHty factors not directly involving internal reactor features. These include feed and product transfer line diameters, inventory control in feed and product separation systems, and preheat and temperature maintenance requirements. Most of these extraneous factors favor large units. Large industrial plants can be operated with high service factors for years, whereas it is not unusual for pilot units to operate at sustained conditions for only days or even hours. 

Alkyl groups under nonacidic conditions sterically deflect nucleophiles from C, but under acidic conditions this steric effect is to some extent offset by an electronic one the protonated oxirane opens by transition states (Scheme 40) which are even more 5Nl-like than the borderline Sn2 one of the unprotonated oxirane. Thus electronic factors favor cleavage at the more substituted carbon, which can better support a partial positive charge the steric factor is still operative, however, and even under acidic conditions the major product usually results from Cp attack. 

The case of a, -unsaturated caAonyl compounds is analogous to that of 1,3-dienes, in that stereoelectronic factors favor coplanaiity of the C=C—C=0 system. The rotamers that are important are the s-trans and s-cis conformations. Microwave data indicate that the s-trans form is the only conformation present in detectable amounts in acrolein (2-propenal). The equilibrium distribution of s-trans and s-cis conformations of a,fi-unsatuiated ketones depends on the extent of van der Waals interaction between substituents. Methyl vinyl ketone has minimal unfavorable van der Waals repulsions between substituents and exists predominantly as the s-trans conformer ... 

Heterocyclic structures analogous to the intermediate complex result from azinium derivatives and amines, hydroxide or alkoxides, or Grignard reagents from quinazoline and orgahometallics, cyanide, bisulfite, etc. from various heterocycles with amide ion, metal hydrides,or lithium alkyls from A-acylazinium compounds and cyanide ion (Reissert compounds) many other examples are known. Factors favorable to nucleophilic addition rather than substitution reactions have been discussed by Albert, who has studied examples of easy covalent hydration of heterocycles. 

There are two types of flexible intermediate drives used to transmit torsional power belt drives and chain drives. Flexible belts are used in industrial power transmission applications primarily when the speeds of the driver and driven shafts must be different or when the shafts must be widely separated. The trend toward higher speed primary drivers and the need to achieve a slower, useful driven speed are additional factors favoring the use of belts. In addition to V-belts, there are round belts and flat belts. Chain drives are typically used in applications where space is limited or obstructions prevent direct coupling of machine-train components. 

How much the energy factor favors the crystal depends upon the change in heat content as a mole of solid dissolves. This change is called the heat of solution. The heats of solution of iodine in these two solvents have been measured they are as follows ... 

We see that there is a much greater energy rise when a mole of I2 dissolves in CCU than when a mole of I2 dissolves in alcohol. Thus the energy factor (favoring the crystal) that opposes the randomness factor (favoring solution) is much... 

However, the situation is not as clear-cut as it might at first seem since a variety of other factors may also contribute to the above-mentioned trend. Abuin et a/.141 pointed out that the transition state for addition is sterically more demanding than that for hydrogen-atom abstraction. Within a given series (alkyl or alkoxy), the more nucleophilic radicals are generally the more bulky (i.e. steric factors favor the same trends). It can also be seen from Tabic 1.6 that, for alkyl radicals, the values of D decrease in the series primary>secondary>tertiary (i.e. relative bond strengths favor the same trend). 

In Reaction 12-9 treatment of Z—CH2—Z with tosyl azide gives diazo transfer. When this reaction is performed on a compound with a single Z group, formation of the azide becomes a competing process. " Factors favoring azide formation rather than diazo transfer include as the enolate counterion rather than Na orLi and... 

In discussing the enviromnental fate of technical DDT, the main issue is the persistence of p,p -DDT and its stable metabolites, although it should be bom in mind that certain other compounds— notably, o,p -DDT and p,p -DDD—also occur in the technical material and are released into the environment when it is used. The o,p isomer of DDT is neither very persistent nor very acutely toxic it does, however, have estrogenic properties (see Section 5.2.4). A factor favoring more rapid metabolism of the o,p isomer compared to the p,p isomer is the presence, on one of the benzene rings, of an unchlorinated para position, which is available for oxidative attack. p,p -DDD, the other major impurity of technical DDT, is the main component of technical DDD, which has been used as an insecticide in its own right (rhothane). p,p -DDD is also generated in the environment as a metabolite of p,p -DDT. In practice, the most abundant and widespread residues of DDT found in the environment have been p,p -DDE, p,p -DDT, and p,p -DDD. 

Figure 2.P25 shows the calculated [B3LYP/6-31G(4,/f)] reaction energy profile for the aldol addition of benzaldehyde and cyclohexanone catalyzed by alanine. The best TSs leading to (S,R) (R,S) (S,S) and (R,R) products are given. What factors favor the observed (R,S) product ... 

Part B of Scheme 4.5 gives some examples of cyclizations induced by selenium electrophiles. Entries 9 to 13 are various selenyletherifications. All exhibit anti stereochemistry. Entries 14 and 15 are selenyllactonizations. Entries 17 and 18 involve amido groups as the internal nucleophile. Entry 17 is an 5-exo cyclization in which the amido oxygen is the more reactive nucleophilic site, leading to an iminolactone. Geometric factors favor N-cyclization in the latter case. 

If HMPA is included in the solvent, the Z-enolate predominates.236,238 DMPU also favors the Z-enolate. The switch to the Z-enolate with HMPA or DMPU is attributed to a looser, perhaps acyclic TS being favored as the result of strong solvation of the lithium ion. The steric factors favoring the -TS are therefore diminished.239 These general principles of solvent control of enolate stereochemistry are applicable to other systems.240 For example, by changing the conditions for silyl ketene acetal formation, the diastereomeric compounds 17a and 17b can be converted to the same product with high diastereoselectivity.241... 

A. Factors Favoring the Stability of Multiple Bonds to the Heavier Main... 

Three factors favored construction of ammonia pipelines. First, over 50% of this country s agricultural nitrogen is used in the Midwest and between 40 and 65% of this total is applied directly to the soil as anhydrous ammonia. Second, the low price of natural gas needed for the production of ammonia favored a Gulf Coast plant site or one near a large gas field. Third, much of the Midwest is inaccessible to cheap barge transportation. 

Although many iterations are usually required in the method of balancing heads, the computation per iteration is simple and fast and the storage requirement is minimal, since no matrix operation or storage is involved. These factors favor the selection of the method of balancing heads, particularly when the program is to be run on a small computer. 

The basicity of the co-fed amine seems to be an important factor favoring... 

Therefore, it has been suggested that electrostatic repulsion by ionized Glu222 is a major stabilization factor favoring the neutral protonated form of the... 

The generalized Woodward-Hoffmann rule suggests that a synchronous addition of disulfonium dications at the double C=C bond of alkenes would be a thermally forbidden process and so would be hardly probable. Simulation of the frontal attack by ethylene on l,4-dithioniabicyclo[2.2.0]hexane 115 gave no optimal structure of an intermediate complex. On the other hand in the lateral approach of the reactants, orbital factors favor attack of the double bond by one of the sulfonium sulfur atoms of the dication. This pattern corresponds to SN2-like substitution at sulfur atom as depicted in Figure 5. Using such a reactant orientation, the structure of intermediate jc-complex was successfully optimized. The distances between the reaction centers in the complex, that is, between the carbon atoms of the ethylene fragment and the nearest sulfur atom of the dication, are 2.74 and 2.96 A, respectively. 

The thermodynamic data presented in Table XYI are calculated for the temperature T=0K. Note that the entropy factor favors betaine decomposition via directions A and B at higher temperatures. The reactions of organoelement analogs of carbenes with phosphorus and arsenic ylides are yet poorly studied. The presented above results of calculations allow an optimistic prognosis about the possibility of developing a new method for the synthesis of elementaolefins R2E14=CH2 (E14 = Si, Ge, Sn) on the basis of these reactions. 

---