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Lec 6 - Seeing Bonds by Electron Difference Density

"Lec 6 - Seeing Bonds by Electron Difference Density" Freshman Organic Chemistry (CHEM 125) Professor McBride uses a 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?" 00:00 - Chapter 1. Understanding Diffraction Patterns: Continuing the Case of the Hexagonal "Benzene" 15:10 - Chapter 2. Double Helices and DNA: Even and Offset Planes 29:04 - Chapter 3. Revealing Bonds and Unshared Electron Pairs via Electron Difference Density Maps 43:23 - Chapter 4. The Second Great Question: "Compared with What?" Complete course materials are available at the Open Yale Courses website: http://open.yale.edu/courses This course was recorded in Fall 2008.

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Lecture list for this course

Lec 1 - How Do You Know?

Lec 2 - Force Laws, Lewis Structures and Resonance

Lec 3 - Double Minima, Earnshaw's Theorem and Plum-Puddings

Lec 4 - Coping with Smallness and Scanning Probe Microscopy

Lec 5 - X-Ray Diffraction

Lec 7 - Quantum Mechanical Kinetic Energy

Lec 8 - One-Dimensional Wave Functions

Lec 9 - Chladni Figures and One-Electron Atoms

Lec 10 - Reality and the Orbital Approximation

Lec 11 - Orbital Correction and Plum-Pudding Molecules

Lec 12 - Overlap and Atom-Pair Bonds

Lec 13 - Overlap and Energy-Match

Lec 14 - Checking Hybridization Theory with XH_3

Lec 15 - Chemical Reactivity: SOMO, HOMO, and LUMO

Lec 16 - Recognizing Functional Groups

Lec 17 - Reaction Analogies and Carbonyl Reactivity

Lec 18 - Amide, Carboxylic Acid and Alkyl Lithium

Lec 19 - Oxygen and the Chemical Revolution (Beginning to 1789)

Lec 20 - Rise of the Atomic Theory (1790-1805)

Lec 21 - Berzelius to Liebig and Wöhler (1805-1832)

Lec 22 - Radical and Type Theories (1832-1850)

Lec 23 - Valence Theory and Constitutional Structure (1858)

Lec 24 - Determining Chemical Structure by Isomer Counting (1869)

Lec 25 - Models in 3D Space (1869-1877); Optical Isomers

Lec 26 - Van't Hoff's Tetrahedral Carbon and Chirality

Lec 27 - Communicating Molecular Structure in Diagrams and Words

Lec 28 - Stereochemical Nomenclature; Racemization and Resolution

Lec 29 - Preparing Single Enantiomers and the Mechanism of Optical Rotation

Lec 30 - Esomeprazole as an Example of Drug Testing and Usage

Lec 31 - Preparing Single Enantiomers and Conformational Energy

Lec 32 - Stereotopicity and Baeyer Strain Theory

Lec 33 - Conformational Energy and Molecular Mechanics

Lec 34 - Sharpless Oxidation Catalysts and the Conformation of Cycloalkanes

Lec 35 - Understanding Molecular Structure and Energy through Standard Bonds

Lec 36 - Bond Energies, the Boltzmann Factor and Entropy

Lec Last - Potential Energy Surfaces, Transition State Theory and Reaction Mechanism