Basicity relative

The relative basicities of aromatic hydrocarbons, as represented by the equilibrium constants for their protonation in mixtures of hydrogen fluoride and boron trifluoride, have been measured. The effects of substituents upon these basicities resemble their effects upon the rates of electrophilic substitutions a linear relationship exists between the logarithms of the relative basicities and the logarithms of the relative rate constants for various substitutions, such as chlorination and... 

While catalytic reduction of the indole ring is feasible, it is slow because of the aromatic character of the C2-C3 double bond. The relative basicity of the indole ring, however, opens an acid-catalysed pathway through 3if-indoleninm intermediates. 

Examine the models of am monia and pyridine on your Learning By Modeling CD Are the calculated charges on nitrogen consistent with their relative basicities What about their electro static potential maps ... 

MX Separation Process. The Mitsubishi Gas—Chemical Company (MGCC) has commercialized a process for separating and producing high purity MX (104—113). In addition to producing MX, this process gready simplifies the separation of the remaining Cg aromatic isomers. This process is based on the formation of a complex between MX and HF—BF. MX is the most basic xylene and its complex with HF—BF is the most stable. The relative basicities of MX, OX, PX, and EB are 100, 2, 1, and 0.14, respectively. 

The Group III peptides come from the 256-amino acid precursor, pro-dynorphin [88402-55-5] (pro-enkephalin B). This group contains dynorphin A [80448-90-4] and B [85006-82-2] as weU as a-neoendorphin [77739-20-9] (Fig. 2), all of which can be further cleaved to form biologically active iatermediates, eg, dynorphin A g and P-neoendorphin [77739-21-0] (a-neoendorphin ) (28). The longer of these peptides are relatively basic because of the number of Lys and Arg residues. 

The relative basicity of PMBs is summarized in Table 4, which shows that basicity increases with increa sing number of methyl groups, and that methyl groups ia the 1,3-position to one another gteatiy influence basicity. 

Exploiting the relative basicity of the xylene isomers, commercial units employ superacids, typically HE—BF, as the acid complexing agent for the separation of / -xylene (feedstock for isophthalic acid) (15). Amoco produces high purity / -xylene at its Texas City facility using the HE—BF process (see Btx processing). Similar processes can be used for the separation of high purity mesitylene and isodurene from their and C q isomers, respectively. 

Table 2. Relative Basicity and Reactivity relative to toluene = 1.00...

Base displacement reactions (70) have been used to estabUsh the relative basicities of a number of ligands toward to be as follows (CgH ) ... 

A comparison of the relative basicities of pyrrole, furan and thiophene may be made by comparing the pK values of their 2,5-di-t-butyl derivatives, which were found to be -1.01, —10.01 and —10.16, respectively. In each case protonation was shown by NMR to occur at position 2. The base-strengthening effect of alkyl substitution is clearly apparent by comparison of pyrrole and its alkyl derivatives, e.g. A-methylpyrrole has a pKa. for a-protonation of -2.9 and 2,3,4,5-tetramethylpyrrole has a pK of 4-3.7. In general, protonation of a-alkylpyrroles occurs at the a -position whereas /3-alkylpyrroles are protonated at the adjacent a-position. As expected, electron-withdrawing groups are base-weakening thus A-phenylpyrrole is reported to have a p/sTa of -5.8. The IR spectrum of the hydrochloride of 2-formylpyrrole indicates that protonation occurs mainly at the carbonyl oxygen atom and only to a limited extent at C-5. 

The relative basicity and acidity of isothiazole and its methyl derivatives have been compared by IR spectroscopy (77MI41702). The isothiazoles, dissolved in inert solvents (e.g. CCI4, CS2) containing traces of butanol (a proton donor), interact with the butanol OH... 

These steric factors are also indicated by the relative basicity of enamines derived from five-, six-, and seven-membered ketones. The five- and seven-membered enamines are considerably stronger bases, indicating better conjugation between the amine lone pair and the double bond. The reduced basicity of the cyclohexanone enamines is related to the preference for exo and endo double bonds in six-membered rings (see Section 3.10). 

The relative basicity of carbonyl oxygen atoms can be measured by studying strength of hydrogen bonding between the carbonyl compound and a hydrogen donor such as phenol. In carbon tetrachloride, values of for 1 1 complex formation for the compounds shown have been measured. Rationalize the observed order of basicity. 

It is hoped that the improvements will help to achieve die objectives for which die text was originally conceived, i.e. to summarize in relatively basic terms die hazards associated with chemicals and how the ensuing risks can be controlled, and to provide sufficient detailed information to supplement that obtainable from suppliers, government publications, trade associations, and computerized data banks where recourse to specialized textbooks may be premature, difficult or unnecessary. 

If relatively basic and nucleophilic aromatic amines are diazotized in nitrosylsul-furic acid, C- instead of TV-nitrosation takes place as shown by Blangey (1938) for 1-naphthylamine, which gave in this system 4-nitroso-l-naphthylamine. A possible mechanistic explanation of Blangey s observation is given in Section 3.2. 

A hydrogen-bond basicity scale has been developed that can be used to determine the relative basicity of molecules. Table 8.2 gives the p hb values for several common heteroatom containing molecules. This is obtained from the protonated form (conjugated acid) of the base in question. The larger the number, the more basic is that compound. 

In concave pyridines [13], the position of the pyridine nitrogen atom is even more defined. A large number of bimacrocyclic concave pyridines [13] were synthesized, and their relative basicities were determined in ethanol these are given in Table 7 (Liining, 1987 Liining et al., 1990, 1991a, 1993). 

Table Relative basicities (log ) of concave pyridines [13] and related compounds [14]-[16] in ethanol.

Table 13 Relative basicities (log )rei of bimacrocyclic (concave) and mono-macrocyclic 1,10-phenanthrolines [29].

For several reasons, this was not surprising. First of all, most of the data on the disposition of nitrosamlnes In plant parts relies on the use of compounds such as NDMA, which, by analogy to Its behavior In animals (24). might be expected to have a short biological half-life In plants It could be especially difficult to detect such compounds when the analyses are performed several weeks after applying the precursors to the plants. In addition, one might expect to find relatively little nitrosatlon of dimethylamlne In a plant, as such relatively basic amines are... 

As explained in Chapter 1, classical preparative layer chromatography (PLC) involves flow of the mobile phase by capillary action. The method uses relatively basic equipment and is not expensive. 

The relatively basic (hydroxyalkyl)phosphines act toward LMCs as reductants and, compatible with this, also as strong nucleophiles. We have studied such reactions in aqueous and D2O solutions by P-, H-, and C-NMR spectroscopies (including 2D correlation methods), product isolation and, when possible, X-ray analysis of isolated compounds or their derivatives. Thus, aromatic aldehyde moieties present in lignin (e.g., 3) are reduced to the corresponding alcohols (see 4) with co-production of the phosphine oxide in D2O, -CH(D)OD is formed selectively (36). The mechanism proceeds via a phosphonium species formed by initial nucleophilic attack of the P-atom at the carbonyl C-atom, i.e., via ArCH(OH)P%, where Ar is the aromatic residue and R is the hydroxyalkyl substituent (36). When the aldehyde contains a 4-OH substituent, the alcohol product... 

Class No. Relative acidity Relative basicity Examples (c, approx.) Characterization ... 

There has been a HO study of the stereoelectronic effects in methy1phosphines (90). Steric effects were found to concentrate in the HOHO and accounted for half the substituent effects on the pK values, whilst electronic effects on the HOHO was minimal.242 The relative basicities of polymethoxytriarylphosphines have been measured. Tris(2,4,6-trimethoxyphenyl)phosphine was considerably more basic than piperidine.243 The basicities of P-N compounds have been reviewed and their correlation with P-N bond lengths invest igated.2 4 4... 

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