Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

Ofial, Armin R.

doi:10.1515/pac-2014-1116

Cited by 14 publications

(5 citation statements)

References 68 publications

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“…This is related to the steric effects arising when the nucleophile is combined with benzhydrylium cations (or structurally related quinone methides). Different steric effects may be expected to impact the reaction rate when used in combination with a different set of electrophiles! Such effects also include noncovalent interactions that can be specific for each nucleophile–electrophile pair . Additional considerations can be made concerning the inclusion of the other parameters.…”

Section: Resultsmentioning

confidence: 99%

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

2021

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The concept of nucleophilicity is at the basis of most transformations in chemistry. Understanding and predicting the relative reactivity of different nucleophiles is therefore of paramount importance. Mayr’s nucleophilicity scale likely represents the most complete collection of reactivity data, which currently includes over 1200 nucleophiles. Several attempts have been made to theoretically predict Mayr’s nucleophilicity parameters N based on calculation of molecular properties, but a general model accounting for different classes of nucleophiles could not be obtained so far. We herein show that multivariate linear regression analysis is a suitable tool for obtaining a simple model predicting N for virtually any class of nucleophiles in different solvents for a set of 341 data points. The key descriptors of the model were found to account for the proton affinity, solvation energies, and sterics.

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Section: Resultsmentioning

confidence: 99%

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

2021

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“…The formation of the carbocation (Ar 2 C H + ) was also detectable by 13 C NMR, showing an iconic chemical shift of 196.6 ppm that was close to the reported values for its analogues , (Figure S2 in the Supporting Information). The strong electrophilicity of such BHD + carbocations is known and has been very well studied, , and they were used as probes for the studies of diverse nucleophiles. For stronger nucleophilic reagents such as thiols (Figure b), the generation rate of thioethers from oxy-BHD + can easily reach the diffusion limit .…”

Section: Resultsmentioning

confidence: 99%

Accelerated Preparation of Polypeptides and Related Hybrid Materials from a Disintegrable Initiator Array with Masked Carbenium Precursors

et al. 2022

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We report a disintegrable initiator array for the synthesis of well-defined polypeptides using raw N-carboxyanhydride monomers that are purified in situ. Free polypeptides can be obtained through the superfast disintegration of the initiation system after polymerization, simultaneously revealing unmasked, highly active benzhydrylium (BHD) ends for efficient conjugation. The polypeptide synthesis and conjugation combined can be accomplished in 3.5 h starting from amino acids. The high activity of BHD on the polypeptides can be utilized to construct complex hybrid materials with ease, shown in two proof-of-concept examples. The BHD-capped polypeptide presents the first reported case of the polymer being used as a dopant, which grafts onto and dopes poly(3-hexylthiophene) directly to give biocompatible, conductive polypeptide brushes. In addition, such polypeptides can directly decorate two-dimensional MoS2 nanosheets for significantly improved dispersibility and activity as a heterogeneous catalyst.

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“…This is possible for the thermometer ions because they present one-product reactions characterized by a loose transition state (TS). Recently, a new set of thermometer ions was proposed, the benzhydrylpyridinium (BhPy) ions, which show lower activation energies than the original BnPy ions due to the addition of an extra phenyl ring that weakens the C–N bond by stabilizing the resultant benzhydrylium ion. , In Scheme , we report the unimolecular fragmentations which characterize these two classes of thermometer ions.…”

Section: Introductionmentioning

confidence: 99%

Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

Malik

Spezia

Hase

2020

J. Am. Soc. Mass Spectrom.

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Thermometer ions are widely used to calibrate the internal energy of the ions produced by electrospray ionization in mass spectrometry. Typically, benzylpyridinium ions with different substituents are used. More recently benzhydrylpyridinium ions were proposed for their lower bond dissociation energies. Direct dynamics simulations using M06-2X/6-31G(d), DFTB, and PM6-D3 are performed to characterize the activation energies of two representative systems: para-methyl-benzylpyridinium ion (p-Me-BnPy + ) and methyl,methyl-benzhydrylpyridinium ion (Me,Me-BhPy + ). Simulation results are used to calculate rate constants for the two systems. These rate constants and their uncertainties are used to find the Arrhenius activation energies and RRK fitted threshold energies which give reasonable agreement with calculated bond dissociation energies at the same level of theory. There is only one fragmentation mechanism observed for both systems, which involves C-N bond dissociation via a loose transition state, to generate either benzylium or benzhydrylium ion and a neutral pyridine molecule. For p-Me-BnPy + using DFTB and PM6-D3 the formation of tropylium ion, from rearrangement of benzylium ion, was observed but only at higher excitation energies and for longer simulation times. These observations suggest that there is no competition between reaction pathways that could affect the reliability of internal energy calibrations. Finally, we suggest using DFTB with modified-Arrhenius model in future studies.

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Benzhydrylium and tritylium ions: complementary probes for examining ambident nucleophiles

Cited by 14 publications

References 68 publications

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

Accelerated Preparation of Polypeptides and Related Hybrid Materials from a Disintegrable Initiator Array with Masked Carbenium Precursors

Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations

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