37 episodes

(CHEM 125) This is the first semester in a two-semester introductory course focused on current theories of structure and mechanism in organic chemistry, their historical development, and their basis in experimental observation. The course is open to freshmen with excellent preparation in chemistry and physics, and it aims to develop both taste for original science and intellectual skills necessary for creative research.

This course was recorded in Fall 2008.

Organic Chemistry - Audio Yale University

    • Science

(CHEM 125) This is the first semester in a two-semester introductory course focused on current theories of structure and mechanism in organic chemistry, their historical development, and their basis in experimental observation. The course is open to freshmen with excellent preparation in chemistry and physics, and it aims to develop both taste for original science and intellectual skills necessary for creative research.

This course was recorded in Fall 2008.

    01 - How Do You Know?

    01 - How Do You Know?

    Professor McBride outlines the course with its goals and requirements, including the required laboratory course. To the course's prime question "How do you know" he proposes two unacceptable answers (divine and human authority), and two acceptable answers (experiment and logic). He illustrates the fruitfulness of experiment and logic using the rise of science in the seventeenth century. London's Royal Society and the "crucial" experiment on light by Isaac Newton provide examples. In his correspondence with Newton Samuel Pepys, diarist and naval purchasing officer, illustrates the attitudes and habits which are most vital for budding scientists - especially those who would like to succeed in this course. The lecture closes by introducing the underlying goal for the first half of the semester: understanding the Force Law that describes chemical bonds.

    • 46 min
    02 - Force Laws, Lewis Structures and Resonance

    02 - Force Laws, Lewis Structures and Resonance

    Professor McBride begins by following Newton's admonition to search for the force law that describes chemical bonding. Neither direct (Hooke's Law) nor inverse (Coulomb, Gravity) dependence on distance will do - a composite like the Morse potential is needed. G. N. Lewis devised a "cubic-octet" theory based on the newly discovered electron, and developed it into a shared pair model to explain bonding. After discussing Lewis-dot notation and formal charge, Professor McBride shows that in some "single-minimum" cases the Lewis formalism is inadequate and salvaging it required introducing the confusing concept of "resonance."

    • 50 min
    03 - Double Minima, Earnshaw's Theorem and Plum-Puddings

    03 - Double Minima, Earnshaw's Theorem and Plum-Puddings

    Continuing the discussion of Lewis structures and chemical forces from the previous lecture, Professor McBride introduces the double-well potential of the ozone molecule and its structural equilibrium. The inability for inverse-square force laws to account for stable arrangements of charged particles is prescribed by Earnshaw's Theorem, which may be visualized by means of lines of force. J.J. Thomson circumvented Earnshaw's prohibition on structure by postulating a "plum-pudding" atom. When Rutherford showed that the nucleus was a point, Thomson had to conclude that Coulomb's law was invalid at small distances.

    • 45 min
    04 - Coping with Smallness and Scanning Probe Microscopy

    04 - Coping with Smallness and Scanning Probe Microscopy

    This lecture asks whether it is possible to confirm the reality of bonds by seeing or feeling them. It first describes the work of "clairvoyant" charlatans from the beginning of the twentieth century, who claimed to "see" details of atomic and molecular structure, in order to discuss proper bases for scientific belief. It then shows that the molecular scale is not inconceivably small, and that Newton and Franklin performed simple experiments that measure such small distances. In the last 25 years various realizations of Scanning Probe Microscopy have enabled chemists to "feel" individual molecules and atoms, but not bonds.

    • 50 min
    05 - X-Ray Diffraction

    05 - X-Ray Diffraction

    Professor McBride introduces the theory behind light diffraction by charged particles and its application to the study of the electron distribution in molecules by x-ray diffraction. The roles of molecular pattern and crystal lattice repetition are illustrated by shining laser light through diffraction masks to generate patterns reminiscent of those encountered in x-ray studies of ordered solids.

    • 47 min
    06 - Seeing Bonds by Electron Difference Density

    06 - Seeing Bonds by Electron Difference Density

    Professor McBride uses an hexagonal "benzene" pattern and Franklin's X-ray pattern of DNA, to continue his discussion of X-ray crystallography by explaining how a diffraction pattern in "reciprocal space" relates to the distribution of electrons in molecules and to the repetition of molecules in a crystal lattice. He then uses electron difference density mapping to reveal bonds, and unshared electron pairs, and their shape, and to show that they are only one-twentieth as dense as would be expected for Lewis shared pairs. Anomalous difference density in the carbon-fluorine bond raises the course's second great question, "Compared to what?"

    • 51 min

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