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Roald Hoffmann

Teoksen The Same and Not the Same tekijä

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Born in Zloczow, Poland, Roald Hoffmann escaped the annihilation of Polish Jews by the Germans during World War II and immigrated to the United States in 1949. He received a B.A. from Columbia University and a Ph.D. from Harvard University. While at Harvard, he and Robert Burns Woodward developed näytä lisää the Woodward-Hoffmann rules on the conservation of orbital symmetry during a chemical reaction by applying principles of quantum theory. These rules enabled scientists to predict an important class of organic reactions. Hoffmann went to work at Cornell University in 1965. In 1981 he shared the Nobel Prize for chemical reaction theory with Kenichi Fukui (who independently had developed an orbital theory in the 1950s). (Bowker Author Biography) näytä vähemmän

Sisältää nimet: Roald Hoffman, Roald Hoffmann

Image credit: Roald Hoffmann

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Associated Works

The Best American Poetry 1994 (1994) — Avustaja — 170 kappaletta
The Best American Science Writing 2003 (2003) — Avustaja — 165 kappaletta
Enrique Martinez Celaya: Poetry in Process (2004) — Avustaja — 12 kappaletta

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I don't know what made me buy this but I'm glad that I did and glad that I've read it. Chemistry is a subject that leaves many people absolutely cold...or frightened. Maybe it's because of the way it's taught at schools or the teachers who purport to teach. Certainly, in the case of my children they were put off the subject by their teachers. And, maybe, it should be taught more along the lines of this book, which I found fascinating. It's written by a Nobel laureate in chemistry who looks at the world of chemistry from the perspective of synthesising molecules and deriving structures. Along the way he discusses isomerism, analytical chemistry, structure of molecules and ways of deriving structures and synthesising them. He finishes up with some philosophical ruminations on the role of chemists in society. Here are some of the take-aways that I had from the book:
"....nature is a tinkerer; the solutions for ensuring survival of a plant or animal are the result of millions of years of random experimentation. The patches on the fabric of life come in a bewildering variety of molecular shapes and colors. Anything that works is co-opted. And banged into shape by all those natural experiments.?
So the realistic question becomes not "What is it?" but "How much is there of what?" One must separate a substance into its constituent components. Each component is a compound, a persistent grouping of atoms that stick together. That group of atoms is called a molecule;.... After separation of a substance into its components, one wants to identify the constituent compounds. To a chemist, structure means the identity of the atoms that are in the pure compound, how those atoms are connected to each other, and what their arrangement in space is..... Illustration 2.2 is the outcome of such a machine at work. This "gas chromatograph" may cost about $5,000. It separates molecules by a repeated process of adsorbing them on little sandlike grains, then releasing them. In this duality of holding on and letting go, different molecules find a different balance and pass through the machine slower or faster".

"The psychology of finding solutions [in terms of analysis] involves a certain mental "drawing of a line," a self-imposed limit on how deep you need to go in. The people who go deeper and deeper are seeking another kind of knowledge than those who want to solve the problem......This brings us to reductionism and ways of understanding. By reductionism I mean the idea that there is a hierarchy of sciences, with an associated definition of understanding and an implied value judgment about the quality of that understanding. That hierarchy goes from the humanities, through the social sciences to biology, to chemistry, physics, and mathematics".

"By further refining, a minute amount of active material [of cockroach sex attractant] was obtained and a structure was proposed on the basis of physical measurements (illustration 5.2).... Within 3 years, six approaches were reported, all most ingenious. Two of them were successful, the others were honourable near misses. So the molecule was well and truly synthesized and the compound became readily available. There was only one snag—the proposed structure was wrong and the synthetic material inactive. A lady I know remarked at the time that, although this molecule wasn't very good at attracting male cockroaches, it certainly attracted a lot of organic chemists....."

Very soon one finds that the rules of the game (very simple-each carbon can form four bonds, each hydrogen one) allow two or more molecules made up of the same atoms, containing the same number and type of bonds, to exist. Thus for CH4H10 we have n-butane and isobutane..... Each has three C-C bonds and ten C-H bonds. Yet they are different; not very different, mind you, but different enough —in their volatility, in the heat generated when these petroleum constituents burn—to matter.....The phenomenon is called isomerism, its elucidation a triumph of nineteenth-century chemistry. Structural isomerism is not the only type of isomerism one has.....There is also geometrical isomerism, exemplified by the two ethylenes substituted by two bromines, as shown in illustration 7.6. Note that in both C,H,Br, isomers the atoms are connected up in the same way, but that there is a difference in geometry-in one case the two bromines are next to each other, in the other case they are opposite.

In the visual system, in the cones and rods of our retina, the energy of the light causes a transformation of one geometrical isomer of a molecule called retinal into another. The change is not that different in its essence from that illustrated for dibromoethylene. A nerve impulse is triggered, and eventually the molecule returns to the original geometry, ready for the next photon.

"......for hydrogen there are three isotopes: normal hydrogen (one electron moving around a nucleus made up of a single proton); "heavy" hydrogen or deuterium (one electron around a nucleus containing one proton and one neutron), and tritium (one electron still, but now a nucleus with one proton, two neutrons). In the official nomenclature of isotopes, the total number of protons and neutrons together is given as a superscript preceding the symbol for the element."......This is why the molecules made of elements that exist in a mixture of isotopes are a wonderful example of the same and not the same.......The isotopic modifications of a molecule are different enough so that we can tell they are there (with an instrument costing a few kilodollars".

The evolutionary tinkering that led to hemoglobin apparently took place in the absence of much carbon monoxide. Then we, humankind, came along, and incomplete combustions occasioned by us and our tools (notably, the automobile engine) now may generate locally high levels of CO...which binds very well to the haemoglobin molecule...much better than oxygen ...and so the organism can be starved of oxygen.

The molecule vibrates; it does not have a static structure. Another chemist comes and says: "You've just drawn the positions of the nuclei. But chemistry is in the electrons. You should draw out the chance of finding them at a certain place in space at a certain time-the electronic distribution." This is attempted in illustration 15.7. I could go on...

Some of the molecules are indeed there, just waiting to be known by us. "Known" in their static properties—what atoms are in them, how these are connected up, the shapes of molecules, their splendid colors....... But so many more molecules of chemistry are made by us, in the laboratory. We're awfully prolific—a registry of known, well-characterized compounds now numbers over ten million. Ten million compounds that were not on earth before!

"....uroporphyrino-gen-Ill (even in the trade, the name of this molecule is abbreviated as uro'gen-lIl). It isn't a glamorous molecule, but it should be. For from this precursor plants make chlorophyll, the basis of all photosynthetic activity. All cells use another uro'gen-Ill derivative in cytochromes for electron transport. And the crucial iron-containing oxygen carrier piece of hemoglobin derives from this small disk-shaped molecule...... How this natural molecule is assembled, within us, is clearly a discovery question...... This incredible but true story was deduced by Battersby and coworkers using a sequence of synthetic molecules, not natural ones." Each was designed to model some critical way station molecule in the living system...... The synthesis of molecules puts chemistry very close to the arts. We create the objects that we or others then study or appreciate..."

....There is high logic in synthetic strategy. The design of a multistep synthesis resembles the making of a chess problem. [In this example] ...at the end is cubane-the mating situation. [a molecule to be synthesised] In between are moves, with rules for making them. The rules are much more interesting and free than those of chess. The synthetic chemist's problem is to design a situation on the chessboard, ten moves back, which has the most ordinary appearance. But from that position, one player (or a team of chemists), by a clever sequence of moves, reaches the mating position no matter what the recalcitant opponent, the most formidable opponent of all, Nature, does.

The isotopic tracers of use in probing the mechanism of the ethane reaction were those of hydrogen, particularly deuterium, or "heavy" hydrogen. Okabe and McNesby took a mixture of normal ethane (CH,) and an ethane in which every last hydrogen was replaced with deuterium (C,D.). Where did they get the "deuterated" compound? They bought it, and back in the laboratories of Merck it was synthesized. What was the first thing they did after they got a sealed flask or ampoule of the gas from the chemical supplier? They probably analyzed it. In this business you do not trust anyone. [I really liked these informal practical details]

Let me restate, in colloquial language, what one might say from Popper's point of view about this beautiful experiment of Okabe and MeNesby: We have, in the weakness of our minds, written down three and only three hypotheses for how ethane might fragment under ultraviolet irradiation. And in the strength and beauty of our hands and our minds, we have constructed experiments to eliminate two such hypotheses. That does not prove the third one at all. There may be a fourth or a fifth one we just were not clever enough to devise......Now, everyone knows that. I know that, the people who did this experiment know that. But these are people who are doing experiments and interpreting them. It is in the nature of people not to want to write wishy-washy conclusions in papers, such as: I have disproven A and B. I hope it's C, but maybe it's something else." No, people want to say, "I have proven C." Scientists want to do something positive.

Note the enormous speed of these molecules; oxygen moves at close to the speed of sound (which is no accident-sound propagation depends on the molecular medium). The molecules don't get very far, however, before they collide with each other. The collision frequency and distance between collisions (called mean free path) do depend on the pressure and temperature of the gas. In outer space, the mean free path would be much, much greater (~10 to power of 9 kilometers in the intergalactic diffuse clouds; a friend remarks, "The poor chaps meet only every few hundred years")...... The average distance between O, molecules in our atmosphere is about 3.5 x 10-7 centimeters. This is about ten times the linear dimension of the molecule. One way to think about it is that the molecules through their rapid motions and collisions bang out an effective space around them that is substantially larger than the space they actually take up.

Enzymes are proteins, chains of amino acids. They are almost entirely made up of C, H, O, N, and S atoms. But often the active site of an enzyme uses essential metal atoms-among others, iron, copper, manganese, molybdenum, magnesium, zinc. Their importance in biological systems does not correlate with their abundance in the crust of the earth.
We eat (we need) proteins. Carboxypeptidase A is a protease, an enzyme that chops up protein by unhooking an amino acid from one end of the polypeptide chain. It specializes, as proteins do, in certain amino acids........ We are curious, we want to know how the enzyme works. To find that out, we certainly want to begin with the enzyme's structure. But we also want to know the shape of the intermediate ES. And ... that is like catching the wind. The enzyme is not called an enzyme for noth-ing— it catalyzes the relevant chemistry most efficiently. ES is there, but ever so fleetingly; the enzyme factory typically processes 100 million molecules a second. [ES is a "complex" of the enzyme with the protein to be degraded, the intermediate.].... In the end Lipscomb's beautiful work has led to a detailed mechanism for carboxypeptidase A's magic cleaving. This is shown in illustration 36.4. The bound enzyme complex (ES) is attacked (top of illustration) by a water molecule that is "activated" by a zine ion and a specific amino acid of the protein, glutamate 270....etc.,.....

About here, Hoffmann verges into philosophical/moral speculation: ......"Sandman points to "outrage factors," all the psychological components of risk perception. Let me choose some from among many he enumerates:......... Diffusion in time and space: Hazard A kills 50 anonymous people a year across the country. Hazard B has one chance in 10 of wiping out its neighborhood of 5,000 people sometime in the next decade. Risk assessment tells us the two have the same expected annual mortality: 50. "Outrage assessment" tells us A is probably acceptable and B is certainly not.

Friends, chemist friends, if someone comes before you verbalizing anxiety over a chemical in the environment, don't harden your hearts and assume a scientistic, analytical stance. Open your hearts, think of one of your children waking at night from a nightmare of being run over by a locomotive. Would you tell him (or her),....."Don't worry, the risk of you being bitten by a dog is greater"?

And his views on climate change ".... What we have added, mostly for the best of reasons, is in danger of modifying qualitatively the great cycles of the planet. The amount of nitrogen fixed from the atmosphere by the Haber-Bosch process, that masterpiece of chemical ingenuity, is, I suspect, comparable to global biological nitrogen fixation." These changes have been wrought in the geological equivalent of the blink of any eye. Gaia may have the restoring forces to deal with our transformations, but the world that results could be one in which humankind will not play a role".
I really liked the book. Five stars from me.
… (lisätietoja)
 
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booktsunami | 1 muu arvostelu | Jan 9, 2024 |
An expensive book, well-bound on thick, glossy paper. The reason for the expensive binding is to present the collages, which I found uninteresting, and all but ignored. The other component of this book is the series of brief chapters by Roald Hoffmann. Many of these are accompanied by diagrams and illustrations from a variety of other sources, some quite interesting. Some are poems, which I ignored. Some are not intended to be read by the audience of the book, like the excerpt from a technical paper about some chemical, but merely to illustrate what these things are like. Some are anecdotes meant to illustrate how chemistry is pursued these days. Some are bits of memoir. Some are historical essays and some are topical essays. These are directed toward the more reflective sort of adult and they can be quite thought provoking. My chemistry background is rather weak, but was sufficient for the book.… (lisätietoja)
½
 
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themulhern | Nov 14, 2016 |
This is an interesting book - a set of covering the intersection between art and science, and what is 'sublime'. Sublime, being a concept that is not too easily defined, and analyzed through philosophy, neuroscience, art, and all that. It's not exactly something that can be easily summarized.
 
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HadriantheBlind | Mar 30, 2013 |
This book is sure interesting, but it lacks some of the style and refinement of the great science book writers.

Sadly, because i am quite interested in chemistry, but the school books were way too dull.
½
 
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acrn | 1 muu arvostelu | Feb 23, 2008 |

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