Isomer distributions

Again the uncertainty about the proportion of an observed result which is due to nitration and the proportion which is due to nitrosation exists. Thus, in expt. 11 phenol was being nitrated above the encounter rate and the observed isomer distribution could arise from a combination of nitration by whatever is the usual electrophile with nitration by a new, less reactive electrophile, or with nitrosation, or all three processes could be at work. 

A careful study of isomer distributions might thus provide information about the structure of the encounter pair. 

The nitration of some substituted nitrobenzenes has been studied in connection with the high o -ratios produced by [ —/ — A/] substituents. Thus nitration in sulphuric acid of 2,5-dialkyl-nitrobenzenes produces the isomer distributions shown below. As has been seen ( 9.1.3), one explanation for the occurrence of high o -ratios with [-/—A/] substituents is that the latter specifically deactivate para positions. In the... 

Some work has been done on the nitration of polyphenyls the case of -terphenyl presents problems in connection with isomer distributions similar to those met with that of biphenyl. 

The nitration of phenylpyridines and related compounds has attracted attention for a long time, and measurements of isomer proportions have been made for several compounds of this type. Nitration occurs in the phenyl ring. For 2-phenylpyridine and 2-phenylpyridine i-oxide measurements of the dependence of rate of nitration upon acidity in 75-81 % sulphuric acid at 25 °C show that both compounds are nitrated as their cations (table 8.1). The isomer distribution did not depend significantly upon the acidity, and by comparison with the kinetic data for quinolinium ( 10.4.2) the partial rate factors illustrated below were obtained.They should be compared with those for the nitration of 2-nitrobiphenyl ( 10.1). The protonated heterocyclic groups are much... 

G. Gomberg reaction. TABLE m-36. EXPERIMENTAL ISOMER DISTRIBUTION. RELATIVE REAC-... 

TABLE in-46. ISOMER DISTRIBUTION OBTAINED DURING THE NITRATION OF PHEN YL-THIA20LES (250)... 

Methylenecyclopentane has the less substituted double bond and is the major product The reported isomer distribution is 91% methylenecyclopentane and 9% 1 methylcyclopentene ... 

To convert kPa to mm Hg, multiply by 7.5. Varies with isomer distribution. 

The alpha-olefin sulfonates (AOS) have been found to possess good salt tolerance and chemical stabiUty at elevated temperatures. AOS surfactants exhibit good oil solubilization and low iaterfacial tension over a wide range of temperatures (219,231), whereas less salt tolerant alkylaromatic sulfonates exhibit excellent chemical stabiUty. The nature of the alkyl group, the aryl group, and the aromatic ring isomer distribution can be adjusted to improve surfactant performance under a given set of reservoir conditions (232,233). 

The methylene-isomer distributions of NaOH and hexa-cataly2ed resoles are shown in Table 6. The distribution of amine stmctures is ... 

DiisononylPhthalate andDiisodeeylPhthalate. These primary plasticizers are produced by esterification of 0x0 alcohols of carbon chain length nine and ten. The 0x0 alcohols are produced through the carbonylation of alkenes (olefins). The carbonylation process (eq. 3) adds a carbon unit to an alkene chain by reaction with carbon monoxide and hydrogen with heat, pressure, and catalyst. In this way a Cg alkene is carbonylated to yield a alcohol a alkene is carbonylated to produce a C q alcohol. Due to the distribution of the C=C double bond ia the alkene and the varyiag effectiveness of certain catalysts, the position of the added carbon atom can vary and an isomer distribution is generally created ia such a reaction the nature of this distribution depends on the reaction conditions. Consequendy these alcohols are termed iso-alcohols and the subsequent phthalates iso-phthalates, an unfortunate designation ia view of possible confusion with esters of isophthaUc acid. 

Butylenes. Butylenes are the primary olefin feedstock to alkylation and produce a product high in trimethylpentanes. The research octane number, which is typically in the range of 94—98, depends on isomer distribution, catalyst, and operating conditions. 

The effect of butene isomer distribution on alkylate composition produced with HF catalyst (21) is shown in Table 1. The alkylate product octane is highest for 2-butene feedstock and lowest for 1-butene isobutylene is intermediate. The fact that the major product from 1-butene is trimethylpentane and not the expected primary product dimethylhexane indicates that significant isomerization of 1-butene has occurred before alkylation. 

Table 2. Isomer Distribution, wt %, of Dodecylbenzene from 1-Dodecene and Benzene...

Processes. Toluene is nitrated ia two stages. Mononitration occurs ia mixed acid, 30% HNO and 55% H2SO4, at 30—70°C ia a series of continuous stirred-tank reactors. Heat is Hberated and must be removed. The isomer distribution is approximately 58% o-nitrotoluene 38% -nitrotoluene, and 4% y -nitrotoluene (Fig. 1). 

Process parameters can be varied to change the MDA isomer distribution and oligomeric content of PMDA products. Generally, aniline to formaldehyde molar ratios of 2 to 5 are used. To increase the MDA content, higher ratios of aniline to formaldehyde are employed. Increasing the acid to aniline ratio also increases the 4,4 -MDA content of the diamine fraction. Historically, the polyurethane industry consumes as much of the 4,4 -MDI isomer as possible. Recently, however, there has been an increasing demand for higher 2,4 -MDI and 2,4 -PMDI products to be used as replacements for... 

The characterizations of MDA and PMDA are similar to those normally used for aromatic amines. In the manufacture of PMDA, the MDA isomer distribution and the formation of side products is deterrnined primarily by gas chromatography (48,49). The amine content is deterrnined by acid titration... 

Table 4. Isomer Distribution and Reactivity Ratio for Selected Reactions ...

Preferably, high pressure Hquid chromatography (hplc) is used to separate the active pre- and cis-isomers of vitamin D from other isomers and allows their analysis by comparison with the chromatograph of a sample of pure reference i j -vitainin D, which is equiUbrated to a mixture of pre- and cis-isomers (82,84,85). This method is more sensitive and provides information on isomer distribution as well as the active pre- and cis-isomer content of a vitamin D sample. It is appHcable to most forms of vitamin D, including the more dilute formulations, ie, multivitamin preparations containing at least 1 lU/g (AOAC Methods 979.24 980.26 981.17 982.29 985.27) (82). The practical problem of isolation of the vitamin material from interfering and extraneous components is the limiting factor in the assay of low level formulations. 

Unesterified tocopherols are found in a variety of foods however, concentration and isomer distribution of tocopherols vary gready with source. Typically, meat, fish, and dairy contain <40 mg/100 g of total tocopherols. Almost all (>75%) of this is a-tocopherol for most sources in this group. The variation in the content of meat and dairy products can be related to the content of the food ingested by the animal. A strong seasonal variation can also be observed. Vegetable oils contain significant levels of y-, P-, and 5-tocopherol, along with a-tocopherol (Table 3). 

Isomerization. Isomerization of any of the butylene isomers to increase supply of another isomer is not practiced commercially. However, their isomerization has been studied extensively because formation and isomerization accompany many refinery processes maximization of 2-butene content maximizes octane number when isobutane is alkylated with butene streams using HF as catalyst and isomerization of high concentrations of 1-butene to 2-butene in mixtures with isobutylene could simplify subsequent separations (22). One plant (Phillips) is now being operated for this latter purpose (23,24). The general topic of isomerization has been covered in detail (25—27). Isomer distribution at thermodynamic equiUbrium in the range 300—1000 Kis summarized in Table 4 (25). 

Noncatalytic ring chlorination of toluene in a variety of solvents has been reported. Isomer distributions vary from approximately 60% ortho in hydroxyhc solvents, eg, acetic acid, to 60% para in solvents, eg, nitromethane, acetonittile, and ethylene dichloride (49,50). Reaction rates are relatively slow and these systems are particularly appropriate for kinetic studies. 

The yield of product is dependent on concentration. An increase in the amount of acetonitrile in Part A to ca. 1000 ml increases the yield of the isomer mixture to 55-75% without affecting Isomer distribution- Further dilution to ca- 5000 mL increases the yield to 80-85%. 

Isomer distribution and purity were assessed by GC (see Note 5). The NMR spectra (in CCI4) for the pure isomers are as follows E-isomer S 5.71... 

C. Relative reactivity and isomer distribution for nitrobenzene and the nitrotoluenes ... 

The chlorination of a series of compounds having electron-withdrawing substituents has been studied. The relative rates of chlorination and the isomer distributions are known. The data give a satisfactory correlation with the Hammett equation using (t, but no rate measurement for benzene under precisely comparable conditions is possible. How could you estimate f,f y and fp for chlorination from the available data ... 

Ammo And Agent Radiochemical Yield (%f 2- Isomer Distribution (%) - 4-... 

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