Beyond the Molecular Frontier Challenges for Chemistry and Chemical Engineering (2003) / Chapter Skim
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4 Chemical and Physical Transformations
4 Chemical and Physical Transformations
Pages 41-54
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4 Chemical and Physical Transformations of Matter GOALS A principal goal of the chemical sciences is to understand and manipulate chemical and physical transformations of matter. We are using the term transfor41
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Catalysis has been key to a large number of new chemical products and processes in the last half century. Catalytic chemical reactors are the central elements in chemical process systems in which thermodynamic phase behavior, flow, heat transfer, and diffusion all play key roles in performance.
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More detailed understanding of quantum mechanical phenomena is essential to a clearer picture of chemical reaction mechanisms and rates. Evidence on the mechanism of reactions can also come from examining the exact molecular geometry of the overall process, its stereochemistry.
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CHEMICAL AND PHYSICAL TRANSFORMATIONS OF MATTER , A: {ION 45 it.
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46 BEYOND THE MOLECULAR FRONTIER Cal+ - calmodulin complex
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CHEMICAL AND PHYSICAL TRANSFORMATIONS OF MATTER 47 3.0 1 n 0.0 o . ~ ionic: Na+ + ICovalent.
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In 1981 Kenichi Fukui and Roald Hoffmann received a Nobel Prize for their theoretical work on the electronic basis of reaction mechanisms for a number of important reaction types. Theory has also been influential in guiding experimental work toward demonstrating the mechanisms of one of the simplest classes of reactions, electron transfer (movement of an electron from one place to another)
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Important physical transformations between states of matter, not necessarily involving chemical reaction, can occur on changes in temperature or pressure or application of external forces or fields. Such phase transitions have been central to quantitative research in chemical sciences, at least since the time of Robert Boyle in the mid-17th century and, in a more modern context, Sadi Carnot, R.J.
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Supercritical carbon dioxide is now used as a solvent in improved, environmentally benign methods for decaffeination of coffee and for dry cleaning (Chapter 9~. Phase behavior in complex fluids such as polymer blends and block copolymers has been a rich area of the chemical sciences.
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The vast effort invested in copolymer microphage separation has recently spawned a number of novel efforts. Studies of the relationship between molecular architecture, ordered-phase morphology, and mechanical properties have shown that multiblock copolymers offer special advantages in product properties that result from the molecular connectivity over the multiple domains that they create.
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CHALLENGES AND OPPORTUNITIES FOR THE FUTURE How can we obtain direct information on the molecular details of a reaction path and harness this for the design of new processes? While femtosecond spectroscopy has made it possible to observe reactions on a short time scale, a major challenge is to devise ultrafast techniques, such as superfast electron diffraction, that will permit observation of the actual molecular structure of a transition state, not just its rate of passage.
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New processes that involve reaction cascades, where the product of one reaction feeds the next, will permit more efficient production of industrial or biomedical products. A detailed understanding of biological metabolic networks will facilitate the design of similarly complex artificial systems.
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WHY ALL THIS IS IMPORTANT Any list of applications such as the examples presented in this chapter is always too limited. It is more realistic to say that there are still big gaps in our understanding of the molecular details of chemical and biochemical reactions.
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