From nitrogen inversion in amines to stereoinversion in aminium salts: role of a single water molecule

Kaur, Ramanpreet; Vikas, .

doi:10.1007/s00214-017-2090-2

Cited by 5 publications

(8 citation statements)

References 42 publications

(70 reference statements)

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“…On a more “mechanistic” side, the flat ammonia sp 2 transition stage between the inverted initial and final sp 3 states would correspond to the “direct” interconversion process, as illustrated here in Figure . However, stereo-inversion pathways with multistep, intermediate stages have been suggested/modeled in more complex substituted amines and their salts that are prone to chiral inversion in the presence of water . These multistep processes would correspond to the more “contorted” route for the nylon interconversion, as suggested in Figure .…”

Section: Discussionmentioning

confidence: 99%

“…However, stereoinversion pathways with multistep, intermediate stages have been suggested/modeled in more complex substituted amines and their salts that are prone to chiral inversion in the presence of water. 58 These multistep processes would correspond to the more "contorted" route for the nylon interconversion, as suggested in Figure 12.…”

mentioning

confidence: 96%

“…In NH 3 , this barrier is 25 kJ/mol or 6 kcal/mol, which is only two times larger than the rotation about a single C−C bond. 58 The corresponding values for the Brill transition are more difficult to identify because the separation between the α to pleated rippled transition and the interconversion process itself have not been clearly identified and thus discriminated. This is clearly a topic for future investigations.…”

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confidence: 99%

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Brill Transition in Nylons: The Structural Scenario()

Lotz

2021

Macromolecules

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Section: Discussionmentioning

confidence: 99%

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confidence: 96%

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confidence: 99%

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Brill Transition in Nylons: The Structural Scenario()

Lotz

2021

Macromolecules

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“…At this point, we reasoned that the protonation of 1 should rigidify its framework and therefore enhance the capsule’s preorganization, enabling it to trap guests. To this end, (1) the quaternary ammonium group from the protonated capsule is unable to invert its configuration (unless it loses the proton), while (2) the likely formation of an ion-paired capsule in nonpolar C 2 D 2 Cl 4 , along with the quaternary nitrogen having “stiffer” bond angles than the tertiary one, could alter the stability of the ground and/or transition state(s) corresponding to its racemization. In this regard, the P / M interconversion of [ 1·H ]–Cl, having an N–H group paired with the chloride anion outside the cavity, was computed (Figure A) to occur via the correlated motion of TPA’s atoms, as in 1 , although with a greater energy of activation of ∼16.2 kcal/mol.…”

Section: Resultsmentioning

confidence: 99%

A Stimuli-Responsive Molecular Capsule with Switchable Dynamics, Chirality, and Encapsulation Characteristics

et al. 2018

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In this study, we report the preparation, conformational dynamics, and recognition characteristics of novel molecular capsule 1 comprising a bowl-shaped framework conjugated to a tris(2-pyridylmethyl)amine (TPA) lid. With the assistance of experiment (H NMR spectroscopy) and theory (MM and DFT) we found that C symmetric 1 is poorly preorganized with three pyridines at the rim adopting a propeller-like orientation and undergoing P-to- M (or vice versa) stereoisomerization (Δ G < 8 kcal/mol, VT H NMR). Capsule 1 binds CH, CHCl, CHCl, CHCl, and CCl with K < 7 M. Protonation of 1 with HCl, however, gives [1·H]-Cl, with the solid-state structure showing the TPA lid being "flattened" and the N-H---Cl hydrogen-bonded group residing outside. Importantly, the P-to- M stereoisomerization would for [1·H]-Cl occur with Δ G = 11 kcal/mol (VT H NMR). Less dynamic and more preorganized [1·H]-Cl binds CH, CHCl, CHCl, CHCl, and CCl guests with a greater affinity ( K = 100-400 M) than 1. The results of our studies suggest that the complexation of increasingly larger guests takes place in an induced-fit fashion, with [1·H]-Cl (a) elongating along its vertical axis and concurrently potentially (b) twisting pyridines from P into M (and vice versa) orientation. The addition of EtN to [1·H]-Cl⊂CHCl causes deprotonation of the capsule and the release of CHCl with the process being fully reversed after the addition of HCl. Allosteric capsule 1 with unique structural and dynamic characteristics is expected to, in the future, assist the construction of complex molecular machines and smart functional materials.

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“…To the best of our knowledge, the present study is the first report which attempts to understand the kinetics of this reaction through advanced rate theories (using spin-unrestricted formalism) while systematically exploring the reaction pathways using global reaction route mapping (GRRM) method, − which will be discussed in detail in the next section. Note that the initial combination of the two radicals (HS and NO 2 ) is believed to be a barrierless process though there may be other reaction pathways which are likely to proceed via transition states with intrinsic energy barrier.…”

Section: Introductionmentioning

confidence: 99%

Conflict in the Mechanism and Kinetics of the Barrierless Reaction between SH and NO₂ Radicals

Kaur

Vikas

2018

J. Phys. Chem. A

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There are some unsettled issues regarding the mechanism and kinetics of an important atmospheric reaction of NO radical with the SH radical. The existing mechanism is based on the formation of HSO and NO radicals, both of which can result only along one barrierless channel. However, the detection of NO radical has never been reported though the formation of HSO radical has been followed in some studies to determine the rate constants. The latter are mainly obtained by monitoring the SH decay, but rate constants are reported to be highly conflicting among the existing studies reporting its value ranging from 10 to 10 cm molecule sec. The present work attempts to resolve these issues by exploring various reaction pathways through the global reaction route mapping of the potential energy surface at the level of spin-unrestricted and spin-restricted coupled-cluster and density functional theories. The initial association of two radicals was found to proceed via two barrierless modes: (1) S-N association leading to HSNO and, (2) S-O association resulting in HSONO, in particular the cis-isomer. The kinetics of the barrierless pathways was investigated through rate constants computed using canonical variational transition state theory (CVTST) along with their temperature and pressure dependence investigated using the master equation. The rate constants calculated using spin-unrestricted methods are found to be in agreement with experimentally observed range of rate constant, and the formation of cis-HSONO (via mode 2) is observed to be the main contributing channel. Contrary to the results of spin-restricted calculations, the barrierless channel (mode 1) leading to the formation of HSNO is predicted to involve two bottlenecks when results using spin-unrestricted calculations were analyzed. Notably, the spin-unrestricted calculations predict a prereaction complex for the formation of S-N bond (via mode 1) which has been treated using Miller's unified transition state theory with a two transition state model. The fate of all the species involved in the reaction is critically evaluated in the present work, and the predictions made can be a subject of further experimental and theoretical studies involving radical-radical reactions.

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From nitrogen inversion in amines to stereoinversion in aminium salts: role of a single water molecule

Abstract: significantly lower the reaction barrier making aminium cation prone to chiral inversion.

Cited by 5 publications

References 42 publications

Brill Transition in Nylons: The Structural Scenario()

Brill Transition in Nylons: The Structural Scenario()

A Stimuli-Responsive Molecular Capsule with Switchable Dynamics, Chirality, and Encapsulation Characteristics

Conflict in the Mechanism and Kinetics of the Barrierless Reaction between SH and NO₂ Radicals

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From nitrogen inversion in amines to stereoinversion in aminium salts: role of a single water molecule

Abstract: significantly lower the reaction barrier making aminium cation prone to chiral inversion.

Cited by 5 publications

References 42 publications

Brill Transition in Nylons: The Structural Scenario()

Brill Transition in Nylons: The Structural Scenario()

A Stimuli-Responsive Molecular Capsule with Switchable Dynamics, Chirality, and Encapsulation Characteristics

Conflict in the Mechanism and Kinetics of the Barrierless Reaction between SH and NO2 Radicals

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Conflict in the Mechanism and Kinetics of the Barrierless Reaction between SH and NO₂ Radicals