R-groups

Fig. X-12. Advancing and receding contact angles of various liquids [water (circles), Gly = glycerol (squares), Form = formamide (diamonds), EG = ethylene glycol (circles), BN = abromonapthalene (squares), BCH = bicyclohexyl (diamond), HD = hexadecane (circles)] on monolayers of HS(CH2)i60R having a range of R groups adsorbed on gold and silver (open and filled symbols respectively). (From Ref. 171.)...

If a catalyst is to work well in solution, it (and tire reactants) must be sufficiently soluble and stable. Most polar catalysts (e.g., acids and bases) are used in water and most organometallic catalysts (compounds of metals witli organic ligands bonded to tliem) are used in organic solvents. Some enzymes function in aqueous biological solutions, witli tlieir solubilities detennined by the polar functional groups (R groups) on tlieir outer surfaces. 

The data led to tire cycle shown in figure C2.7.8. Here, only tire active site on tire interior enzyme surface (section C2.6) is depicted, consisting of R groups including aspartic acid, glutamic acid and otliers, represented witli tire shortliand Asp, Glu etc tire subscripts represent tlie positions on tlie polypeptide chain. 

Patent databases are therefore integrated databases because facts, text, tables, graphics, and structures are combined. In patents that include chemical aspects (mostly synthesis or processing), the chemical compounds are often represented by Markush structures (see Chapter 2, Section 2.7.1). These generic structures cover many compound families in a very compact maimer. A Markush structure has a core structure diagram with specific atoms and with variable parts (R-groups), which are defined in a text caption. The retrieval of chemical compounds from Markush structures is a complicated task that is not yet solved completely satisfactorily. 

Figure 10.3-39. A substructure search in a catalog of fine chemicals. The precursor illustrated may be needed for the synthesis of a library, A substructure is defi ned by setting an open site at the position of the R group. Some representative examples of the 69 compounds in the Acros catalog which were obtained are shown.

If the thiazole under consideration reacts in its neutral form, the ring nitrogen is expected to be reactive center. Exceptions could be expected for 2-araino-4-R thiazoies with bulky R groups and for electrophilic reactants able to generate a carbocation. 

For 2-R-substituted 4-phenylthiazoles, the influence of R groups on the yield of substitution has been reported (see Table III-47). Substitution occurred at the para-position of the phenyl ring (249). 

TABLE IIM7. INELUENCE OF 2-R GROUP DURING THE NITRATION OF 2-R-4-PHENYL rai AZOLES... 

When more than one R group is present the groups may be the same or different Most compounds have more than one acceptable name... 

Both R groups are usually the same although they need not always be... 

Tetrasubstituted alkene (Section 5 6) Alkene of the type R2C=CR2 in which there are four carbons directly bonded to the carbons of the double bond (The R groups may be the same or different)... 

In reverse-phase chromatography, which is the more commonly encountered form of HPLC, the stationary phase is nonpolar and the mobile phase is polar. The most common nonpolar stationary phases use an organochlorosilane for which the R group is an -octyl (Cg) or -octyldecyl (Cig) hydrocarbon chain. Most reverse-phase separations are carried out using a buffered aqueous solution as a polar mobile phase. Because the silica substrate is subject to hydrolysis in basic solutions, the pH of the mobile phase must be less than 7.5. 

The Chains and Averages of Polymers Table 1.3 Name, Abbreviation, and R Group for Some Common Amino Acids ... 

Construct such a model for isotactic polypropylene. Estimate the volume of an isobutyl group on the scale of your model and examine whether interference between successive substituents would occur if this were the R group present. 

The electron-releasing R group helps stabilize this cation. As with anionic polymerization, the separation of the ions and hence the ease of monomer insertion depends on the reaction medium. The propagation reaction may be written as... 

R groups alkyl alkyl or aryl with substituents alkyl... 

By way of example, tert-huty peroxyacetate [107-71-1] is more thermally stable than 3-hydroxy-1,1-dimethylbutyl peroxyneoheptanoate [110972-57-1]. Although other factors affect thermal stabiUty, the trends shown can be used to quaUtatively predict peroxyester reactivity trends. The order of activity of the R group ia peroxyesters is also observed ia other / fZ-aLkylperoxy-containing compounds. 

Changing the stmcture of R affects the activity of monoperoxycarbonates as previously discussed for peroxyesters. The other cogenerated radical is an alkoxycarbonyloxy radical. The nature of the R group has practically no effect on the reactivity of monoperoxycarbonates having the same 00-tert-55ky group. The 10-h half-life temperature remains at 100°C for almost ah. 00-tert-huty O-alkyl monoperoxycarbonates. 

Acyl Side-Chain Reactions. Many reactions occur in the R group of the fatty acid residue (see Carboxylic acids Fats and fatty oils). 

Alkoxy radicals from hydroperoxides can undergo a -scission reaction (eq. 2) to yield an alkyl radical and a ketone. The higher stabiUty of the generated alkyl radical compared to that of the parent alkoxy radical provides the driving force for this reaction, and the R group involved is the one that forms the most stable alkyl radical. 

Dialkyl peroxides have the stmctural formula R—OO—R/ where R and R are the same or different primary, secondary, or tertiary alkyl, cycloalkyl, and aralkyl hydrocarbon or hetero-substituted hydrocarbon radicals. Organomineral peroxides have the formulas R Q(OOR) and R QOOQR, where at least one of the peroxygens is bonded directly to the organo-substituted metal or metalloid, Q. Dialkyl peroxides include cyclic and bicycflc peroxides where the R and R groups are linked, eg, endoperoxides and derivatives of 1,2-dioxane. Also included are polymeric peroxides, which usually are called poly(alkylene peroxides) or alkylene—oxygen copolymers, and poly(organomineral peroxides) (44), where Q = As or Sb. 

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