Development of the HERON Reaction: A Historical Account

2017 ◽  
Vol 70 (4) ◽  
pp. 344 ◽  
Author(s):  
Stephen A. Glover
Keyword(s):  
Driving Force ◽  
Reactive Intermediates ◽  
Acyl Derivative ◽  
Historical Account ◽  
Amide Nitrogen ◽  
Chronological Order ◽  
Carbonyl Carbon ◽  
Time Line ◽  
Basic Understanding ◽  
Deficient Group

This account describes the discovery and development of the HERON reaction, a reaction with special connection to the Heron Island Conferences on Reactive Intermediates and Unusual Molecules. This modern ‘named’ reaction describes an unusual rearrangement of bisheteroatom-substituted amides RCON(X)(Y) whereby the more electron deficient group, X, migrates from nitrogen to the carbonyl carbon giving an acyl derivative, RC(O)X, and Y-stabilised nitrenes. In it, the origins, mechanistic elucidation, and theoretical validation are described in more or less chronological order. Along that time line we introduce the concepts of ‘anomeric amides’, ‘amidicity’ in anomeric amides, and their role in the HERON reaction. All known versions of the reaction that have since been discovered are outlined and a basic understanding of the relative roles of reduced resonance and the anomeric driving force, both functions of the heteroatom substituents at the amide nitrogen, are quantified.

scholarly journals The role of substituents in the HERON reaction of anomeric amides

2016 ◽  
Vol 94 (12) ◽  
pp. 1169-1180 ◽  
Author(s):  
Stephen A. Glover ◽  
Adam A. Rosser
Keyword(s):  
Molecular Conformation ◽  
Minor Role ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Activation Barriers ◽  
Resonance Energies ◽  
Electronegative Atom ◽  
A Minor ◽  
Bound Electron

Anomeric amides, RCON(X)(Y), have two electronegative atoms at the amide nitrogen, a configuration that results in greatly reduced amide resonance and strongly pyramidal nitrogen atoms. This, combined with facilitation of anomeric interactions, can result in the HERON reaction, an intramolecular migration of the more electronegative atom, X, from nitrogen to the carbonyl with production of a Y-stabilised nitrene. We have modelled, at the B3LYP/6-31G(d) level, a variety of anomeric amides that undergo the HERON reaction to determine factors that underpin the process. The overriding driving force is anomeric destabilisation of the bond to the migrating group. Rotated transition states show loss of residual resonance and this is a component of the overall activation energies. However, the reduced resonance in these systems plays only a minor role. We have determined the resonance energies (RE) and HERON activation barriers (EA) of five anomeric systems. REs for the amides have been calculated isodesmically using our calibrated trans amidation method and COSNAR calculations. Reduction of their overall EAs by the corresponding RE gives rearrangement energies (Erearr.), a measure of relative impact on rearrangement of substituents on nitrogen. In CH3CON(OMe)(Y) systems producing (CH3CO2Me + NY), a loosely bound electron pair on the donor atom, Y, in nY–σ*NOMe anomeric interactions drives the reaction. Erearr. increases in the sequence Y = N(nitrene) < O−(oxide) ≪ NMe2 < SMe ≪ OMe. For the same systems, RE increases in the order Y = N < O− ≪ OMe ≪ NMe2 ∼ SMe. Other effects such as molecular conformation, nature of the migrating group, X, and acyl substituents at the carbonyl carbon are discussed.

London

2021 ◽  
pp. 136-178
Author(s):  
Thomas Albert Howard
Keyword(s):  
British Empire ◽  
Driving Force ◽  
Interreligious Dialogue ◽  
Keynote Speaker ◽  
Historical Account ◽  
Close Attention ◽  
World Congress ◽  
Religious Traditions ◽  
The World ◽  
First Time

This chapter spotlights a major interreligious event that took place in 1924: the Conference on Some Living Religions within the Empire. It notes that the conference brought representatives from major religious traditions of the British Empire — excluding Christianity and Judaism because of their presumed familiarity — to London to expound before a general British audience the chief tenets and practices of their faiths. For many attendees, it was their first time to hear directly from a Muslim, a Hindu, a Buddhist, and a Parsi, among other religious voices. In addition to offering a historical account of this conference, the chapter discusses its legacy — the main one being the creation of the World Congress of Faiths (1936), the oldest continuously existing organization devoted to interreligious dialogue. It also pays close attention to Sir Francis Younghusband (1863–1942), the keynote speaker at the 1924 conference and the driving force behind the establishment of the congress in 1936. Ultimately, the chapter investigates why the conference deserves recognition alongside Chicago's better-known parliament of 1893.

scholarly journals Molecular mechanisms of cobalt-catalyzed hydrogen evolution

2012 ◽  
Vol 109 (38) ◽  
pp. 15127-15131 ◽  
Author(s):  
Smaranda C. Marinescu ◽  
Jay R. Winkler ◽  
Harry B. Gray
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Driving Force ◽  
Molecular Mechanisms ◽  
Reactive Intermediates ◽  
Cobalt Complexes ◽  
Resonance Spectroscopy ◽  
Acidic Solutions ◽  
Reaction Free Energy ◽  
Competing Pathways

Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV/Co. Protonation of CoI produces a transient CoIII-H complex that was characterized by nuclear magnetic resonance spectroscopy. The CoIII-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that CoIII-H produces hydrogen by two competing pathways: a slower homolytic route involving two CoIII-H species and a dominant heterolytic channel in which a highly reactive CoII-H transient is generated by CoI reduction of CoIII-H.

scholarly journals Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

Molecules ◽  
2018 ◽  
Vol 23 (11) ◽  
pp. 2834 ◽  
Author(s):  
Stephen Glover ◽  
Adam Rosser
Keyword(s):  
Amide Bond ◽  
Anomeric Effect ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Heteroatom Substitution ◽  
Electronegative Atom ◽  
Anomeric Effects ◽  
Acyl Derivatives

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide. However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically. In certain configurations, reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen) reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. In other cases the anomeric effect facilitates SN1 and SN2 reactivity at the amide nitrogen.

Disaster Cinema. A Historical Overview

2020 ◽  
Author(s):  
Nikita Mathias
Keyword(s):  
Technological Innovation ◽  
Historical Overview ◽  
Historical Account ◽  
Chronological Order ◽  
Catastrophic Events ◽  
Economic Profit ◽  
Cultural Events ◽  
The Sublime ◽  
History Of ◽  
Aesthetic Characteristics

The aim is to give a historical account of the disaster movie genre in chronological order, in continuation of the cultural and technological history of sublime disasters. The films in question employ the receptive and general aesthetic characteristics of the sublime for their depictions of catastrophic events. My discussion also includes the specific media technological environments in which the films were performed, insofar as cinema’s potential to function as a medium of the sublime represents the receptive foundation of the films. What is excluded from this historical account is the interpretations of the films’ disasters as allegories of specific contemporary political and socio-cultural events. In opposition to these (often premature) readings, one must take the immediate sensuality and the receptive tactics of disaster films seriously and elucidate the genre’s transformations by reference to the mechanisms of economic profit and technological innovation and application.

scholarly journals Heteroatom Substitution at Amide Nitrogen — Resonance Reduction and HERON Reactions of Anomeric Amides

2018 ◽  
Author(s):  
Stephen A. Glover ◽  
Adam A. Rosser
Keyword(s):  
Amide Bond ◽  
Anomeric Effect ◽  
Amide Nitrogen ◽  
Carbonyl Carbon ◽  
Heteroatom Substitution ◽  
Electronegative Atom ◽  
Anomeric Effects ◽  
Acyl Derivatives

This review describes how resonance in amides is greatly affected upon substitution at nitrogen by two electronegative atoms. &nbsp;Nitrogen becomes strongly pyramidal and resonance stabilisation, evaluated computationally, can be reduced to as little as 50% that of N,N-dimethylacetamide.&nbsp;&nbsp;However, this occurs without significant twisting about the amide bond, which is borne out both experimentally and theoretically.&nbsp;&nbsp;In certain configurations,&nbsp;reduced resonance and pronounced anomeric effects between heteroatom substituents are instrumental in driving the HERON (Heteroatom Rearrangement On Nitrogen)&dagger; reaction, in which the more electronegative atom migrates from nitrogen to the carbonyl carbon in concert with heterolysis of the amide bond, to generate acyl derivatives and heteroatom-substituted nitrenes. &nbsp;In other cases the anomeric effect facilitates S&shy;N1 and SN2 reactivity at the amide nitrogen.

scholarly journals Reactive intermediates. Some chemistry of quinone methides

2000 ◽  
Vol 72 (12) ◽  
pp. 2299-2308 ◽  
Author(s):  
Y. Chiang ◽  
A. J. Kresge ◽  
Y. Zhu
Keyword(s):  
Acid Catalysis ◽  
Isotope Effects ◽  
Reactive Intermediates ◽  
Quinone Methide ◽  
Carbonyl Carbon Atom ◽  
Carbonyl Carbon ◽  
Quinone Methides ◽  
Rate Determining Step ◽  
Energy Relationships ◽  
Acid Catalyzed

Quinone methides were produced in aqueous solution by photochemical dehydration of o-hydroxybenzyl alcohols (o-HOC6H4CHROH; R = H, C6H5, 4-CH3OC6H4), and flash photolytic techniques were used to examine their rehydration back to starting substrate as well as their interaction with bromide and thiocyanate ions. These reactions are acid-catalyzed and show inverse isotope effects (kH+/kD+ < 1), indicating that they occur through preequilibrium protonation of the quinone methide on its carbonyl carbon atom followed by rate-determining capture of the benzyl carbocations so formed by H2O, Br-, or SCN-. With some quinone methides (R = C6H5 and 4-CH3OC6H4) this acid catalysis could be saturated, and analysis of the data obtained in the region of saturation for the example with R = 4-CH3OC6H4 produced both the equilibrium constant for the substrate protonation step and the rate constant for the rate-determining step. Energy relationships comparing the quinone methides with their benzyl alcohol precursors are derived.

In situ TEM Studies of agglomeration of sub-nanometer Ru layers in Ru/C multilayers

1992 ◽  
Vol 50 (1) ◽  
pp. 256-257
Author(s):  
Tai D. Nguyen ◽  
Ronald Gronsky ◽  
Jeffrey B. Kortright
Keyword(s):  
Layered Structure ◽  
Driving Force ◽  
High Energy ◽  
Superior Performance ◽  
In Situ Tem ◽  
Rayleigh Instability ◽  
Practical Applications ◽  
Transmission Electron ◽  
Diffraction Patterns

Nanometer period Ru/C multilayers are one of the prime candidates for normal incident reflecting mirrors at wavelengths < 10 nm. Superior performance, which requires uniform layers and smooth interfaces, and high stability of the layered structure under thermal loadings are some of the demands in practical applications. Previous studies however show that the Ru layers in the 2 nm period Ru/C multilayer agglomerate upon moderate annealing, and the layered structure is no longer retained. This agglomeration and crystallization of the Ru layers upon annealing to form almost spherical crystallites is a result of the reduction of surface or interfacial energy from die amorphous high energy non-equilibrium state of the as-prepared sample dirough diffusive arrangements of the atoms. Proposed models for mechanism of thin film agglomeration include one analogous to Rayleigh instability, and grain boundary grooving in polycrystalline films. These models however are not necessarily appropriate to explain for the agglomeration in the sub-nanometer amorphous Ru layers in Ru/C multilayers. The Ru-C phase diagram shows a wide miscible gap, which indicates the preference of phase separation between these two materials and provides an additional driving force for agglomeration. In this paper, we study the evolution of the microstructures and layered structure via in-situ Transmission Electron Microscopy (TEM), and attempt to determine the order of occurence of agglomeration and crystallization in the Ru layers by observing the diffraction patterns.

The nucleation of cavities at grain boundaries

1987 ◽  
Vol 45 ◽  
pp. 288-291
Author(s):  
P. J. Goodhew
Keyword(s):  
Surface Tension ◽  
Surface Energy ◽  
Grain Boundaries ◽  
Radiation Damage ◽  
Impurity Concentration ◽  
Driving Force ◽  
Nucleation And Growth ◽  
Phase Boundaries ◽  
Cavity Nucleation ◽  
Spherical Bubble

Cavity nucleation and growth at grain and phase boundaries is of concern because it can lead to failure during creep and can lead to embrittlement as a result of radiation damage. Two major types of cavity are usually distinguished: The term bubble is applied to a cavity which contains gas at a pressure which is at least sufficient to support the surface tension (2g/r for a spherical bubble of radius r and surface energy g). The term void is generally applied to any cavity which contains less gas than this, but is not necessarily empty of gas. A void would therefore tend to shrink in the absence of any imposed driving force for growth, whereas a bubble would be stable or would tend to grow. It is widely considered that cavity nucleation always requires the presence of one or more gas atoms. However since it is extremely difficult to prepare experimental materials with a gas impurity concentration lower than their eventual cavity concentration there is little to be gained by debating this point.

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