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Articles by Roald Hoffmann
A 21st Century View of Allowed and Forbidden Electrocyclic Reactions
The Woodward–Hoffmann (W–H) publications of 1965 and thereafter clearly distinguished between “allowed” and “forbidden” pericyclic reactions. (1−10) R. B. Woodward and Roald Hoffmann defined “pericyclic reactions” as “reactions in which all first-order changes in bonding relationships take place in concert on a closed curve.” (9,11) Their first communication in 1965 (4) introduced the idea of electronic control of stereoselectivity of cyclizations that they named electrocyclizations.
A 21st Century View of Allowed and Forbidden Electrocyclic Reactions
The Woodward–Hoffmann (W–H) publications of 1965 and thereafter clearly distinguished between “allowed” and “forbidden” pericyclic reactions. (1−10) R. B. Woodward and Roald Hoffmann defined “pericyclic reactions” as “reactions in which all first-order changes in bonding relationships take place in concert on a closed curve.” (9,11) Their first communication in 1965 (4) introduced the idea of electronic control of stereoselectivity of cyclizations that they named electrocyclizations.
Poem: ‘sap pitch and resin’
Science in meter and verse Credit: MirageC Getty Images Edited by Dava Sobel First it fell just fell at my feet no wind no squirrel or bird to give it a push a green green pine cone with brown accents heavy with sealed overlapping rounded rhomboid structures in spirals I have to restrain myself from seeing here the condensed aromatic hydrocarbons I leave it on a plate and look on the web for the names of cone parts names are important even if my last name changed three times what I learn is...
Correction to “Squeezing All Elements in the Periodic Table: Electron Configuration and Electronegativity of the Atoms under Compression”
Page 10266. Figure 16 shows incorrect data for Pu and Cm. The corrected Figure 16 shows data that agrees with the description in the article text, which is correct. The authors apologize for the error and for any inconvenience caused. Figure 16 Figure 16. Change in average electron energy, Δχ, upon compression of row 7 f-block elements Pu and Cm relative to the atoms in vacuum. Δχ > 0 means electron destabilization, i.e., decreasing electronegativity.
An Octet in Flushing Meadows
In the spring of 1939, as the world emerged from the Great Depression and braced itself against the threat of impending war, the United States hosted an optimistic exhibition of a brighter future. The 1939 New York World’s Fair was a showcase of economic might, nationalism, culture, and modernist and art deco design. Visitors arriving in Flushing, Queens, by subway entered the fairgrounds through the Community Interests zone.
Simulation vs. Understanding: A Tension, in Quantum Chemistry and Beyond. Part B. The March of Simulation, for Better or Worse
Essay Roald Hoffmann Corresponding Author E-mail address: rh34@cornell.edu http://orcid.org/0000-0001-5369-6046 Dept.
Simulation vs Understanding A Tension, in Quantum Chemistry and Beyond. Part A. Stage Setting
Essay PDF PDF Share Abstract We begin our tripartite essay with a triangle of understanding, theory and simulation. We sketch the intimate tie between explanation and teaching, and point to its emotional content.
Simulation vs Understanding A Tension, in Quantum Chemistry and Beyond. Part C. Toward Consilience
Essay PDF PDF Share Abstract In the last part of our essay, we outline a future of consilience, with a role both for fact‐seekers, and for searchers for understanding. We begin by looking at the surroundings of theory and simulation, their environment in fact shaped by experiment, especially in Chemistry. Experimenters ask questions both conceptual and numerical, and so bring the communities together.
The Squeeze Is On
Scientists love subjecting matter to extreme conditions. And the variable of pressure, at its high end, is perhaps the most interesting one to explore for both chemistry and physics. For although we can estimate the (very short) lifetimes of molecules at temperatures of the sun, and what chemistry might transpire at a nanokelvin or in a vacuum “higher” than that of outer space, the realm of high pressure, such as that at the center of a planet, gives us pause.
The Metaphor, Unchained
This Article From Issue September-October 2006 Volume 94, Number 5 Scientists write, first of all for other scientists. It's not publish or perish, but rather that an open system of communication, a commitment (shading to an addiction) to telling others what you have done, is essential to the functioning of science. The primary medium of communication in the profession is the peer-reviewed article. This, our stock in trade, has a ritual format with strong historical roots.
Squeezing All Elements in the Periodic Table: Electron Configuration and Electronegativity of the Atoms under Compression
We present a quantum mechanical model capable of describing isotropic compression of single atoms in a non-reactive neon-like environment. Studies of 93 atoms predict drastic changes to ground-state electronic configurations and electronegativity in the pressure range of 0–300 GPa. This extension of atomic reference data assists in the working of chemical intuition at extreme pressure and can act as a guide to both experiments and computational efforts.
Squeezing all Elements in the Periodic Table: Electron Configuration and Electronegativity of the Atoms under Compression
RETURN TO JUST ACCEPTED MANUSCRIPTSPREVArticleNEXT Martin Rahm Roberto Cammi Neil W. Ashcroft Roald Hoffmann LEARN ABOUT THESE METRICS Article Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days. Citations are the number of other articles citing this article, calculated by Crossref and updated daily.
Angewandte Chemie International Edition in English
Review The Conservation of Orbital Symmetry† Prof. R. B. Woodward Corresponding Author Department of Chemistry, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138 (USA) R. B. Woodward, Department of Chemistry, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138 (USA) Roald Hoffmann, Department of Chemistry, Cornell University, Ithaca, New York 14850 (USA) Search for more papers by this author Prof.
The Devil Teaches Thermodynamics: Sean Ono Lennon Reads Nobel-Winning Chemist and Poet Roald Hoffmann’s Ode to Entropy
“We must be less than death to be lessened by it — for nothing is irrevocable but ourselves,” Emily Dickinson wrote of what she so stunningly termed “the drift called the infinite.” And yet we are, of course, less than death — we are inherently revocable, for death is the sole inevitability of life. For Dickinson, the irrevocability of human life was to be found in the living — in the truth and beauty we cast ourselves upon, in the loves we love.
Coping with Fritz Haber's Somber Literary Shadow
Picture(s) of Fritz Haber: Rolf Hochhuth, Tony Harrison, and André Malraux—three very different writers—have portrayed Fritz Haber in their novels and plays. The picture may not please chemists. Several biographies and an essay by the historian Fritz Stern have also dealt with Haber's tragic life. Should we accept these as literary portraits, if they are not to our liking? Or struggle with them? And in Haber's case would this be justified?
Electronegativity Seen as the Ground-State Average Valence Electron Binding Energy
We introduce a new electronegativity scale for the atoms, based consistently on ground state energies of valence electrons. The scale is closely related to (yet different from) L.C. Allen’s, which is based on configuration energies. Using a combination of literature experi- mental values for ground state energies and ab initio calculated energies where experimental data are missing, we are able to provide electroneg- ativities for elements 1-96.
Editorial: What, Another Nobel Prize in Chemistry to a Nonchemist?
Corresponding Author E-mail address:rh34@cornell.edu Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853‐1301 (USA) Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853‐1301 (USA)Search for more papers by this author
Building Bridges Between Inorganic and Organic Chemistry (Nobel Lecture)
Robert B. Woodward, a supreme patterner of chaos, was one of my teachers. I dedicate this lecture to him, for it is our collaboration on orbital symmetry conservation, the electronic factors which govern the course of chemical reactions, which is recognized by half of the 1981 Nobel Prize in Chemistry. From Woodward I learned much: the significance of the experimental stimulus to theory, the craft of constructing explanations, and the importance of asethetics in science.
Building Bridges Between Inorganic and Organic Chemistry (Nobel Lecture)
Robert B. Woodward, a supreme patterner of chaos, was one of my teachers. I dedicate this lecture to him, for it is our collaboration on orbital symmetry conservation, the electronic factors which govern the course of chemical reactions, which is recognized by half of the 1981 Nobel Prize in Chemistry. From Woodward I learned much: the significance of the experimental stimulus to theory, the craft of constructing explanations, and the importance of asethetics in science.
Abstract Science?
This Article From Issue November-December 2009 Volume 97, Number 6 Is there an analogue in science to abstract art? A riposte might be, “Why should there be? Why ask science, so strongly tied to reality, to mimic the aesthetic games of the world of art?” Well, both art and science are created by human beings, and both are creative endeavors. So it might be interesting to look at any correspondences.
Chemical & Engineering News
It was in a villa on Lake Geneva in 1816. It was “a wet, ungenial summer, and incessant rain often confined us for days,” remembers Mary Wollstonecraft Godwin. They were sitting together—Godwin; her soon-to-be husband Percy Bysshe Shelley; the poet Lord Byron; and John William Polidori, a physician and writer credited with pioneering the vampire novel. As the group sought diversion, Lord Byron decreed, “We will each write a ghost story.” Mary, all of 18, actually finished one.
Time Brings Change
Time does indeed fly. Some days it soars, some days it rockets. Its incessant progression motivates us to manage it. We share our time, track our time, and schedule our time. No matter how hard we try to slow it down, there’s no stopping it. Meanwhile, each passing moment brings a new experience that deserves our attention. That is, until the next moment displaces it. And so it goes. We have now reached the year 2015.
The Tensions of Scientific Storytelling
Simplicity pleases the mind. Some scientists claim that equations are likely to be correct because they are simple, or that molecules naturally assume more symmetric arrangements of atoms, or that multistep mechanisms for chemical reactions are less common than concerted one-fell-swoop reactions. What happens when the scientist’s hard work reveals that the equation is messy, the molecule looks like an odd clump of pasta, and the mechanism has at least 17 steps?
The Many Guises of Aromaticity
This Article From Issue January-February 2015 Volume 103, Number 1 Aromaticity is one of the core concepts of organic chemistry. The idea began as a descriptor of the special stability of the ring of six carbons, benzene, C6H6. And importantly, of the ability of that ring to be transformed by chemically substituting the hydrogens attached to it. The reactions involved were relatively easy, the products often stable and useful.
Learning and Teaching Strategies
This Article From Issue September-October 2010 Volume 98, Number 5 Learning and teaching science challenges many students as well as instructors. We have been teaching and helping others to teach chemistry at every level—from high school teachers to undergraduate and graduate students to university faculty—for over four decades. From that experience have come a number of teaching and learning tactics that we find effective in facilitating student learning.
Structural Diversity and Electron Confinement in Li4N: Potential for 0-D, 2-D, and 3-D Electrides
In pursuit of new lithium-rich phases and potential electrides within the Li–N phase diagram, we explore theoretically the ground-state structures and electronic properties of Li N at P = 1 atm. Crystal structure exploration methods based on particle swarm optimization and evolutionary algorithms led to 25 distinct structures, including 23 dynamically stable structures, all quite close to each other in energy, but not in detailed structure.
<em>Homo citans</em> and carbon allotropes
Today, routine quantum chemistry and physics is much easier than experiment. Ergo several hundred papers out there on hypothetical carbon allotropes. Clad verbally in every enhancer you can imagine, to be sure. The first of these being novelty. Yet roughly half of such structures, beautiful as they are, have been in the literature before. Unbeknownst to their authors; no malice at work, just laziness.
Linearly Polymerized Benzene Arrays As Intermediates, Tracing Pathways to Carbon Nanothreads
How might fully saturated benzene polymers of composition [(CH) ] form under high pressure? In the first approach to answering this question, we examine the stepwise increase in saturation of a one-dimensional stack of benzene molecules by enumerating the partially saturated polymer intermediates, subject to constraints of unit cell size and energy.
Chemical & Engineering News
This guest editorial is by Roald Hoffmann and Bassam Z. Shakhashiri. Hoffmann is a Nobel Laureate in Chemistry and the Frank H. T. Rhodes Professor of Humane Letters Emeritus in the department of chemistry and chemical biology at Cornell University. Shakhashiri was ACS president in 2012 and is the William T. Evjue Distinguished Chair for the Wisconsin Idea in the department of chemistry at the University of Wisconsin, Madison.
Chemical & Engineering News
This guest editorial is by Roald Hoffmann and Bassam Z. Shakhashiri. Hoffmann is a Nobel Laureate in Chemistry and the Frank H. T. Rhodes Professor of Humane Letters Emeritus in the department of chemistry and chemical biology at Cornell University. Shakhashiri was ACS president in 2012 and is the William T. Evjue Distinguished Chair for the Wisconsin Idea in the department of chemistry at the University of Wisconsin, Madison.
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