N-Tritylhydroxylamines: preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

Canle, Moisés; Clegg, William; Demirtaş, İbrahim; Elsegood, Mark R. J.; Maskill, Howard; Miatt, Peter C.

doi:10.1039/b103569j

Cited by 12 publications

(15 citation statements)

References 22 publications

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“…Three principal causes of each change in the PA have been identified, and their relative contributions differ according to the nature of the structural modification. These are: i) destabilisation of the lone pair of the basic site, as in the change from NH 3 to CH 3 NH 2 and tricyclohexylmethylamine, ii) relaxation effects in the radical cation after electron loss, as in the increasing PAs along the series CH 3 NH 2 , PhCH 2 NH 2 , Ph 2 CHNH 2 and Ph 3 CNH 2 , and iii) changes in the bond energy term as the radical cation bonds to the hydrogen atom, as in the higher basicity of oxygen in relation to nitrogen in acetamide (6) and the higher basicity at N than at O in hydroxylamine. In some cases it is not possible to identify a single dominant term, implying that interplay of two or even three terms is of importance.…”

Section: Summary and Concluding Remarksmentioning

confidence: 98%

“…Similarly, but to a smaller degree, N-trityl groups enhance the base strengths of hydroxylamines. [6] The unifying feature of our measurements is that a (substituted) N-trityl group increases the base strengths of weakly basic amines, hydroxylamines and amides in solution, and the effect is greater when the original base-weakening structural feature exerts its effect through resonance (the arylamines and amides) than by induction (hydroxylamines). It was unclear at the time whether the anomalously high base strengths of these N-trityl compounds were due to intrinsic steric or electronic molecular effects, or to peculiarities arising out of aqueous solvation phenomena.…”

Section: Introductionmentioning

confidence: 96%

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Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

2006

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An ab initio theoretical method based on a triadic formula has been employed to calculate changes in proton affinities (PAs) after sequential substitution of C-H by C-phenyl in methylamine and in the N-methyl component of N-methylacetamide. The overall objective was to investigate the cause of the recently reported unexpected basicity-enhancing effect of the N-trityl group in several amines and in acetamide. The triadic method indicates that the increase in PA from NH 3 to CH 3 NH 2 is principally due to destabilisation of the lone pair, compensated to some degree by a smaller bond energy term. The increasing PAs along the series CH 3 NH 2 , PhCH 2 NH 2 , Ph 2 CHNH 2 and Ph 3 CNH 2 are mainly due to an increasing relaxation energy effect following increasing phenyl substitution, supported by increasing bond energy terms. Introduction of para-methoxy substituents in tritylamine would be calculated to result in small incremental increases in PA, in agreement with experimental findings. The PA of tricyclohexylmethylamine (233.6 kcal·mol -1 ) is calculated to be similar to that of trimethoxytritylamine (233.5 kcal·mol -1 ), a consequence of the destabilisation of the lone pair on nitrogen by the three bulky cyclohexyl groups. Results for acetamide indicate that protonation on oxygen is

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Section: Summary and Concluding Remarksmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 96%

Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

2006

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“…They not only are the first hydrocarbon ions ever recognized but are also important reagents and catalysts for numerous synthetic transformations . The parent tritylium ion as well as its substituted derivatives has been used for hydride abstractions as well as for the protection of OH and NH groups . Ionization equilibria of triarylmethanols were the basis of Deno's acidity function H R originally designated as C 0 , and rate constants of the reactions of tritylium ions with nucleophiles represent the major source of data from which Ritchie derived N + parameters for nucleophiles from constant selectivity relationships …”

Section: Introductionmentioning

confidence: 99%

A comprehensive view on stabilities and reactivities of triarylmethyl cations (tritylium ions)

Horn

Mayr

2012

J of Physical Organic Chem

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By combining conventional photometric and conductimetric methods with stopped‐flow techniques, we were able to investigate ionization rate constants of trityl bromides, chlorides, and carboxylates in aqueous acetonitrile in a reactivity range from 10−5 to 103 s−1. In this way, it became possible to compare ionization processes yielding tritylium ions which differ by 21 units in pKR+, corresponding to 120 kJ mol−1 in free energy. Analysis of such far‐reaching correlations provided new insights into several aspects of organic reactivity. We observed (i) the change of solvolysis mechanisms from SN1 reactions without and with common ion return, (ii) reactions where formation and consumption of the carbocations could be observed visually, (iii) solvolyses where the ionization step is almost complete before the reaction with water becomes significant, and (iv) ionizations that yield solutions of persistent carbocations. The continuous change from reactions with carbocation‐like transition states to reactions with transition states of little carbocation character caused large variations of Winstein–Grunwald m values. Values of m = 0.2 for ionization processes show that low values of m do not necessarily imply SN2 reactions. Although the 4,4′,4″‐trimethoxytritylium ion reacts more than 1000 times faster with water than the 4‐dimethylaminotritylium ion and has a pKR+ value that is more negative by three units, both carbocations are formed with almost equal rates by ionization of the corresponding acetates in aqueous acetonitrile. This comparison again illustrates that electrofugality is not simply the inverse of electrophilicity and presents a challenge for further study of the importance of intrinsic barriers. Copyright © 2012 John Wiley & Sons, Ltd.

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“…These reactions (e.g. equation 10) are practically feasible only for compounds forming highly stabilized carbocations such as trityl 46,47 , or 2-(p-alkoxyphenyl)propyl 48 . All these reactions proceed exclusively on the nitrogen atom and have been used for N-protection of the amino groups in hydroxylamines.…”

Section: Otfmentioning

confidence: 99%

Synthesis of Hydroxylamines

Melman

2010

Patai's Chemistry of Functional Groups

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Introduction Hydroxylamines through Hydrolysis of Hydroxamic Acids, Oximes and Nitrones Synthesis of Hydroxylamines through Alkylation and Arylation of other Hydroxylamines Hydroxylamines through Reduction Reactions Hydroxylamines through Addition to the C  N Double Bond of Oximes, Oxime Ethers and Nitrones Hydroxylamines through Addition to the N  O Double Bond of Nitroso and Nitro Compounds Hydroxylamines through Oxidation of Amines Hydroxylamines through Cycloaddition Reactions

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N-Tritylhydroxylamines: preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

Cited by 12 publications

References 22 publications

Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

A comprehensive view on stabilities and reactivities of triarylmethyl cations (tritylium ions)

Synthesis of Hydroxylamines

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