Substitution/conversion

Heterocyclic compound Alkyl radical Radical source Method (Section II, B) Position of substitution (%) Conversion (%) Yield (%) Ref. 

Acid-Strengthening ring substituents also retard electrophilic, and enhance nucleophilic, aromatic substitution. Conversely, the acid-weakening groups accelerate electrophilic, and retard nucleophilic, aromatic substitution. 

AcEIYLKETENE, 21, 64 Acetylsalicylyl chloride, 23, 66 Acetylsalicylyl peroxide, 23, 66 Acetyl-o-toluidine, 22, 94 substituted, conversion to indoles, 22, 95... 

The effect of the heteroatom is to make the pyridine ring very unreactive to normal electrophilic aromatic substitution. Conversely, pyridines are susceptible to nucleophilic attack. These topics are discussed later. 

Alkyne ligands are sometimes susceptible to direct ligand substitution. Conversion of bisalkyne monomers to monoalkyne complexes is particularly common for cyclopentadienyl derivatives (72) as discussed in Section II,C. Displacement of the lone alkyne from CpML(RC=CR)X complexes has rarely been reported. Similar results are characteristic of alkynes in M(RC=CR)2(CO)LX2 (49), where one alkyne is labile, compared to M(RC=CR)(CO)L2X2 which is resistant to alkyne substitution. 

Different types of substitution/conversion-editing have been described. The best characterised involves cytidine deamination to uridine in the editing of transcripts for apolipoprotein B, and adenosine deamination to inosine in the editing of the transcripts encoding the glutamate receptor subunits. More than 90 different types of base modifications have been described. Moreover, methylations and substitutions of the ribose and phosphate moieties have also been identified. Recently, the 2 -0-ribose methylation has been the focus of much attention since the discovery that the snoRNA guides the methylation in a frans-acting fashion. 

Acceptable accuracy and parallelism of the C-terminus assay are likely due to the C-terminal specificity of the capture antibody and the N-terminal location of the norleucine substitutions. Conversely, with the N-terminal specific assay, dramatic differences in recoveries were seen for the two forms of the drug, a direct consequence of these N-terminal modifications and differential binding of the immunoreagent directed at this region. Although each assay demonstrated good linearity upon... 

Figure 5 Ti-substitution conversion of a Ti04 tetradron sharing edges with two neighboring S1O4 tetrahedra into a regular comer-sharing TO4 network...

This PE is described in the USP as the sodium salt of polycarboxymethyl ether of cellulose. Its typical molecular weight is 90.000-700.000. The rheological properties of CMC depend on the polymer concentration and on the degree of substitution (conversion of -OH into -0-CH2-COO ) which varies from 0.5 to 1.2 [35, 36]. Thus, various grades of CMC with different aqueous viscosities are available, currently regarded as low-, medium-, and high-viscosity (CMC-Na (LV), CMC-Na (MV) and CMC-Na (HV), respectively). At 1 % w/v aqueous concentration they yield the viscosities described in Table 2 [10]. 

To be effective in delocalizing charge in the intermediate, the electron-withdrawing groups must by ortho or para to the group we wish to substitute. Conversely, electron donors at the ortho- or pora-positions retard reaction. Groups at the meto-position have little effect. 

---