Conformational dynamics and strain Johannes Wislicenus 1835-1902 "specially directed forces, the affinity-energies” are responsible for torsional motions in a molecule (vibrational, rotational, angular …) Need not think about molecules as static in 2D! Ring strain … aka angle strain … aka Baeyer strain Adolf von Baeyer (1853-1917) Recognized the strain that must be present in small rings Dye synthesis Nobel Prize 1905 Pics: Wikipedia Cyclohexane as a chair? Herman Sachse 1890 Realized cyclohexane need not be planar, Conformational isomers would alleviate strain! (At left, Hernán Sachse) Zeitschrift für physicalische chemie, 10, 201-241 (1892) Sachse’s problem: Organic chemists don’t math so good. Cyclohexane as a chair? 1918: structural proof for the “chair” … diamond! Odd Hassel (1897-1981) Determined cyclohexane structure and fluxionality Published in Norwegian Sir Derek Barton (1918-1998) Conformational Analysis He read the Scandinavian lit! Shared the 1969 Nobel Prize Pics: Wikipedia Fused rings – decalin system: cortisone Thank you Google image search Stereoisomerism proposals 1874 Joseph Achille Le Bel Jacobus Henricus van’t Hoff 1847-1930 1852-1911 (France) (The Netherlands) “La chimie dans l’espace” First Nobel Prize Pics: Wikipedia Manuscript reviews: ca. 1874 "A Dr. J. H. van ’t Hoff of the Veterinary School at Utrecht has no liking, apparently, for exact chemical investigation. He has considered it more convenient to mount Pegasus (apparently borrowed from the Veterinary School) and to proclaim in his ‘La chimie dans l’espace’ how, in his bold flight to the top of the chemical Parnassus, the atoms appeared to him to be arranged in cosmic space." Hermann Kolbe, senior editor of the Journal für Praktische Chemie Chiral discrimination Jones, Organic Chemistry 2nd ed. Fig. 4.26 Importance of chirality Smell: R-carvone: S-carvone: spearmint caraway Toxicity of a morning sickness drug: Harmless to fetus Teratogen: limb defects “Therapeutics:” Vick’s inhaler meth Cahn-Ingold-Prelog 1950-1955 Robert Sidney Cahn Sir Christopher K. Ingold Vladimir Prelog 1899-1981 1893-1970 1906-1998 (R-S naming from R.S.?) Reaction mechanisms Nobel Prize 1975 Pics: Wikipedia.