catalysts such as enzymes to the design of new catalysts for industrial processes. A century ago, chemists had only begun to interpret chemical transformations in terms of atoms, molecules, and chemical bonds—and now they are seeking ways to observe the details of reaction for an individual molecule. Dramatic changes have taken place in the chemical and physical processing of materials, where product properties and flow characteristics can be understood on the basis of intermolecular forces. This fundamental understanding can be used to design manufacturing methods with unprecedented reliability. In both synthesis and manufacturing, biochemical methods are increasingly important.

The time scales for which measurements are made also have undergone a phenomenal evolution. A hundred years ago, it was difficult to measure events taking place at a time scale of less than a second, and by the middle of the 20th century, the limit had changed by only a few orders of magnitude. But as described in Chapter 4, advances in the chemical sciences have moved the frontier to the investigation of processes that take place on the femtosecond (10⁻¹⁵ s) time scale—the time scale at which individual chemical bonds are made and broken. We conclude that the opportunities for detailed understanding of chemical reaction pathways and of the mechanisms of physical transformations represent an exciting challenge for the future that will add to the fundamental science of our field and to its ability to manipulate reactions and processes for practical applications.

The broad topic of analysis is treated in Chapter 5, which covers isolating, identifying, imaging, and measuring chemical substances and determining their molecular structures. The changes in capability and methodology are astounding. A century ago, Jacobus van’t Hoff and Emil Fischer received the first two Nobel prizes in chemistry, respectively, for proposing the theory of tetrahedral carbon and for synthesizing all eight stereoisomers of glucose to corroborate that theory. These “simple” determinations of chemical structure required years of work. By the mid-20th century, spectroscopic techniques had made it possible to investigate far more complicated structures, and to detect them at much lower levels. But measurements at the parts per million level were still a challenge, and structure determination was no easy task—even when nuclear magnetic resonance became available in the 1960s. Chemical instrumentation has changed the frontiers for measurement in astonishing ways since then. The speed of measurements has been reduced from hours to small fractions of a second, and measurements can be repeated quickly to provide high throughput for multiple samples. The control of chemical processes in real time is drastically improved with new measurement techniques. Routine analysis can be done on samples in the range of milligrams to micrograms rather than on samples of a gram or more. The size of molecules that can be analyzed in detail has grown from organic molecules with molecular weights of several hundred daltons to proteins and nucleic acid polymers that are millions of times larger. And the sensitivity of modern instruments has moved the frontiers of detection from the level of one mole toward that of a