Trimethylammonium ions

Kinetic data are available for the nitration of a series of p-alkylphenyl trimethylammonium ions over a range of acidities in sulphuric acid. - The following table shows how p-methyl and p-tert-h xty augment the reactivity of the position ortho to them. Comparison with table 9.1 shows how very much more powerfully both the methyl and the tert-butyl group assist substitution into these strongly deactivated cations than they do at the o-positions in toluene and ferf-butylbenzene. Analysis of these results, and comparison with those for chlorination and bromination, shows that even in these highly deactivated cations, as in the nitration of alkylbenzenes ( 9.1.1), the alkyl groups still release electrons in the inductive order. In view of the comparisons just... 

Nucleophiles can also act as acids and bases, and this behavior substantially alters their nucleophilicity. At pH 5, trimethylamine exists mainly as its conjugate acid, trimethylammonium cation. First draw a Lewis structure, and then examine the electrostatic potential for trimethylammonium ion. On the basis of the map, which is the better nucleophile, the cation or the corresponding neutral amine At pH 12, phenol exists mainly as its conjugate base, phenoxide anion. First draw a Lewis structure (or series of Lewis structures), and then examine the electrostatic potential map for phenoxide anion. Which is the better nucleophile, phenoxide or phenol ... 

Electrostatic potential map for trimethylammonium ion shows most positively-charged regions (in blue). 

Examine atomic charges and display electrostatic potential maps for ammonium and trimethylammonium ions (protonated ammonia and trimethylamine, respectively). How many acidic hydrogens are there in each Assuming that solvent coordinates to acidic hydrogens, how many solvation sites are there in each ... 

Ar-Cl), as compared to their reactivities with an anionic nucleophile. The reaction of 108 with trimethylamine at the pam-posi-tion contrasts with that of 2,4-dichloronitrobenzene which reacts with a large variety of nucleophiles at the oriA.o-position. Compared to the (2,6-dinitrophenyl)trimethylammonium ion, steric hindrance to activating resonance would be much less in 2-trimethyl-ammoniopyrimidine. 

Hammet and collaborators140, 141 studied in more detail the hydrolysis of aliphatic esters with a cation-exchange resins as catalyst. They found that replacement of 70% of the hydrogen ions in a crosslinked polystyrenesulfonic add by cetyl-trimethylammonium ions had a specifically favorable effect on the effectiveness of the remaining hydrogen ions for the hydrolysis of ethyl-n-hexanoate. From these findings, the important contributions of the hydrophobic forces, in addition to the electrostatic forces, is clearly demonstrated. 

In each case, the N atom is sp hybridized, with one lone pair of electrons and three o-bonds. A quaternary ammonium ion is a tetrahedral ion of the form R4N, where as many as three of the R groups (which may all be different) can be replaced by H atoms. For example, the tetramethylammonium ion, (CH3)4N+, and the trimethylammonium ion, (CH3)3NH+, are quaternary ammonium ions. The amino group, the parent functional group of amines, is —NH2. 

Syn elimination and the syn-anti dichotomy have also been found in open-chain systems, though to a lesser extent than in medium-ring compounds. For example, in the conversion of 3-hexyl-4-d-trimethylammonium ion to 3-hexene with potassium ec-butoxide, 67% of the reaction followed the syn-anti dichotomy. In general syn elimination in open-chain systems is only important in cases where certain types of steric effect are present. One such type is compounds in which substituents are found on both the P and the y carbons (the unprimed letter refers to the branch in which the elimination takes place). The factors that cause these results are not completely understood, but the following conformational effects have been proposed as a partial explanation. The two anti- and two syn-periplanar conformations are, for a quaternary ammonium salt ... 

It was only around 1850 that the first amines were discovered by Wurtz [2], who considered them as alkylated (or arylated) derivatives of NH3. Nowadays, it is well known that the amine function is widespread among biologically important compounds, but mostly it is present in polyfunctional molecules such as amino acids, alkaloids, etc. Simple amines are very rare in nature, with the exception of tri-ethylamine and the trimethylammonium ion which come from the putrefaction of proteins. 

At this point the hygroscopic potassium salt may be isolated and dried, or, more conveniently, the potassium salt may be dissolved in water and the carborane anion precipitated with one of a variety of large cations, such as the rubidium, cesium, tetramethylammonium, or trimethylammonium ions. The tri-methylammonium salt of the carborane anion is useful because it is readily purified by recrystallization from water and may be easily converted in solution to salts containing other counterions. ... 

Fig. 9. Stabilizing interactions of trimethylammonium ion of a substrate analogue with Glu4, Tyr56, and Phe66 of PLCa. [45]...

It was found that a better representation of non-specific interactions between solvents and the monosubstituted dipolar trimethylammonium ions is gained from the product of tt and the solvent dipole moment (/x). The obtained results were compared with the gas-phase basicity and the solvent attenuation factors (SAF) were calculated". 

In previous studies we have described the binding of alkyl-trimethylammonium ions to a variety of polyanions (16-19). As has been observed by other authors, both the alkyl chainlength dependence and the ionic-strenght dependence of the binding process... 

After allowing for a statistical correction for the number of protons that may be lost from the cation, the order of acid strengths (per NH-proton) of these cations remains unchanged. The initial trend of decreasing acidity with methyl substitution is reversed in the trimethylammonium ion, because with a decreasing number of protons in the cation, its hydration stabilization by hydrogen... 

Solution We assume that ammonium halide salts are completely dissociated to give (CH3)3NH+ and Cl. We then recognize that trimethylammonium ion is a weak acid, being the conjugate acid of trimethylamine, (CH3)3N, a weak base. Cl- has no basic or acidic properties and should be ignored. In Appendix G, we find trimethylammonium ion listed as trimethylamine, but drawn as trimethylammonium ion, with pA"a = 9.799. So,... 

Other substrates, in which one of the two nucleofuges is not a halogen, have been studied. Haloarene-diazo sulfides on treatment with arenethiolate ions give substantial formation of bis(arylthio)arenes except that the monofluorophenyl sulfide is produced when the halogen is fluorine,64 and p-iodophenyl-trimethylammonium ion, on treatment with benzenethiolate ion in liquid ammonia, gives p-bis(phenyl-thio)benzene in 95% yield.90... 

The question as to whether all of the possible iWmethylation compounds of noradrenaline are indeed commonly present in storage places in the body such as the adrenal medulla, or the carotid body, or other ganglia or peripheral synapses will probably not be answered soon, for the intensity of the pharmacological activity of iV -dimethylnoradrenaline and noradrenaline trimethylammonium ion is not great as reported by Stehle, Melville, and Oldham (14) who unfortunately do not give any of the chemical details regarding the identity or purity of the preparations they used. 

The entropy difference of 15 e.u. is due to the three additional water molecules which are frozen in the ionization of the trimethylammonium ion. Trotman-Dickenson has pointed out, however, that the observed values of ACp, if interpreted in terms of hydrogen bonding, lead to results opposed to those deduced from entropy changes. They are, however, explicable on the basis of restricted internal rotations. 

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