Title A Brief History of Organic Chemistry

Phlogiston/Stahl The Phlogiston Theory metal + heat = calx of metal + Ø e.g., zinc = zinc oxide + Ø phlogiston (Ø) is lost calx + charcoal(Ø) + heat = metal + (fixed air) phlogiston (Ø) is gained The Phlogiston (Gr., to set on fire) Theory was prevalent in the 18th century. When metals were heated in air, a calx was formed (an oxide today) and phlogiston was lost. Since the calx was always heavier than the metal, phlogiston must have a negative mass. Carbon (charcoal) was rich in phlogiston because when it was heated with a calx (phlogiston poor), the metal (rich in phlogiston) along with “fixed air (CO2)”was formed. Problem: phlogiston has a negative mass! Georg Ernest Stahl (1660-1734)

Priestley The Co-Discoverer of Oxygen Trained in the ministry Studies on the nature of air - 1775 Mercurius calcinatus + heat = Mercury + dephlogisticated air HgO + heat = Hg + O Priestley heated red mercuric oxide in a sealed system to produce liquid, metallic mercury and dephlogisticated air (oxygen). The mass of the vessel did not change. He also noted that dephlogisticated air was essential for breathing. In spite of these observations, he nonetheless remained a supporter of the Phlogiston Theory. Recognized the role of oxygen in the life cycle Told Lavoisier of his findings Joseph Priestley (1733-1804) Held to the phlogiston theory until his death

Lavoisier Lavoisier and Combustion Quantitative methods Mass is conserved Combustion is not a loss of phlogiston but a gain of oxygen. Traité de Chimie - 1789 Priestley informed Lavoisier of his experiments. Lavoisier was able to demonstrate that mass is conserved in chemical reactions. The calxhas a higher mass than the metal from which it is derived. It is oxygen that is gained, not phlogiston that is lost. Antoine-Laurent Lavoisier (1743-1794) and His Wife (Marie-Anne-Pierrette Paulze, 1758-1836), 1788 Jacques-Louis David (French, 1748-1825) Dual names for salts Guillotined 1794 www.metmuseum.org

Dalton/Atomic Theory Atomic Theory 1. Elements composed of indivisible atoms 2. Elements have defined and different masses 3. Elements combine in simple numerical ratios - Law of Multiple Proportions Dalton proposes the atomic theory in the eary 19th century. Uses circles for the various elements. Hydrogen = 1 Azot = 4.2 Carbone = 4.3 Oxygen = 5.5 John Dalton (1766-1844)

Rule of Greatest Simplicity The Rule of Greatest Simplicity For Water: 1g of H / 8g of O Formula = HO But: 1g of H / 2 x 4g of O Formula = HO2 Dalton proposes the Rule of Greatest Simplicity, which held that water was a binary compound of the formula OH. This in spite of the fact that the French chemist, Gay-Lussac, was able to electrolyze water into two volumes of hydrogen and one of oxygen. Or: 2 x 1g of H / 16g of O Formula = H2O

Dylan Thomas "One Christmas was so much like another, in those years around the sea-town corner now and out of all sound except the distant speaking of the voices I sometimes hear a moment before sleep, that I can never remember whether it snowed for six days and six nights when I was twelve or whether it snowed for twelve days and twelve nights when I was six." "A Child's Christmas in Wales" --- Dylan Thomas Is carbon mass 6 or 12?

Berzelius Electrochemical Theory Chemical analysis Modern symbols of the elements Discovers: Ce, Se, Th, Si, Zr, etc. Defines isomerism Berzelius provided the modern symbols of the elements and defined isomerism (equal parts). Isomers have the same composition but not the same physical properties. Dualism held that organic compounds, like inorganic ones, had electropositive and electronegative componnets. Electrochemical Theory (Dualism) Jons Jacob Berzelius (1779-1848)

Electrochemical Theory Electrochemical Theory (Dualism) Salts Acid Base Non-metal + Oxygen Radical + Oxygen Metal + Oxygen

Wohler 1828 The Beginning of the End for Vitalism 1828 - Converts ammonium cyanate CH4N2O (inorganic) into urea CH4N2O (organic) Friedrich Wöhler (1800 - 1882) Vitalism held that organic compounds (derived from living or deceased organisms) were different from inorganic compounds. The formation of urea (organic) from ammonium cyanate (inorganic) countered this argument. Berzelius, Wohler’s mentor, expressed support of the experiment as an example of isomers An example of isomers Begins the downfall of Vitalism

Artificial urea On the Preparation of “Artificial” Urea: I cannot, so to say, hold my chemical water and I must tell you that I can make urea without needing to have kidneys, or anyhow, an animal, be it human or dog. Wohler’s message to Berzelius. 1828 - Wöhler to Berzelius For more from the wry pen of Wöhler.

Radical Theory Radical Theory Refined chemical analysis Developed laboratory instruction Trained many of the chemists of the day Liebig revolutionized chemical analysis so that it could be conducted on small samples. He set forth modern laboratory instruction. Proponent of Radical Theory along with Dumas Justus Liebig (1803-1873)

Benzoyl Radical The Benzoyl Radical 1832 - Liebig and Wöhler Benzoyl hydride C7H5O - H (Oil of bitter almond, Benzaldehyde) Benzoyl hydroxide C7H5O - OH (Benzoic acid) Radical Theory (Liebig and Dumas) held that in organic chemistry radicals are complex; in inorganic chemistry they are simple. The benzoyl radical is comprised of C, H, O in fixed amounts. Radicals were thought to be immutable. Benzoyl chloride C7H5O - Cl Benzamide C7H5O - NH2

Dumas/Liebig 1837 1837 - Dumas and Liebig Note on the Present State of Organic Chemistry In mineral chemistry the radicals are simple; in organic Chemistry the radicals are compound; that is all the difference. The laws of combination and of reaction are otherwise the same in these two branches of chemistry. Leicester and Klickstein, A Source Book of Chemistry, 1400 - 1900. Harvard, 1952)

Substitution Theory Substitution Theory 1838 - chlorination of acetic acid C4H4O2 + Cl6 = C4HCl3O2 + H3Cl3 C = 6, O = 16 One experiment too many! Dumas chlorinates acetic acid. Only some of the hydrogens are replaced by chlorine. Liebig held that electronegative atoms could not be substituted for electropositive ones. Melsen (1842) converts trichloroacetic acid into acetic acid by the action of zinc. C2H4O2 + 3Cl2 = C2HCl3O2 + 3HCl J. B. Dumas (1800 -1884)

Ammonia Type Type Theory 1850 - The ammonia type Hofmann studies amines. A series of amines have similar properties. This is the amine type. A series of ethylamines can be formed by successive alkylations with ethyl iodide. August Wilhelm von Hofmann (1818-1892)

Water Type The Water Type 1850 - 1852 butyl alcohol butyl alcohol + butyl alcohol + butyl alcohol + ether Williamson attempts to make n-butyl alcohol from ethanol as accomplished by Hofmann in the amine series. He discovers a new route to ethers and defines the water type. Alexander Williamson (1824-1904) An expanded version of the ether story

Valence/Frankland Valence 1852 - recognizes the ability of N, P, As, and Sb to combine with 3 and 5 other elements. 1857 - Kekule develops the idea of valence with carbon compounds. Frankland introduces the concept of valence. Edward Franklin (1825 - 1899)

Kekule 1858 - Quadravalence of carbon 1865 - Structure of benzene 1861 - Lehrbuch der Organischen Chemie Acetic Acid Kekule establishes the tetravalence of carbon and the structure of benzene. Friedrich August Kekule (1829-1896)

Kekule’s 19 formulas for acetic acid (C2H4O2) from his Lehrbuch der Organischen Chemie 1867 (pg. 164 & 165)

Couper 1858 1858 Acetic Acid Atoms with lines between them (1831-1892) Couper uses lines to connect atoms. Note: C=12; O=8. Atoms with lines between them (1831-1892)

Loschmidt 1861 Physicist and Chemist 1861 - Diagrammatical Structural Formulae of Organic Chemistry Acetic Acid Loschmidt uses diagrammatic formulas. There is evidence that the more well known Kekule read Loschmidt’s work. Joseph Loschmidt (1821 - 1895)

Crum Brown 1865 1865 Acetic Acid Alexander Crum Brown (1838-1922) Crum Brown: atom connectivity and multiple “bonds” . Alexander Crum Brown (1838-1922) Atom connectivity Multiple connections

van’t Hoff 1874 1874 - The Arrangement of Atoms in Space Carbon is tetrahedral! Carbon is not only tetravalent but also tetrahedral. Jacobus Henricus van’t Hoff (1852 - 1911) 1901 - 1st Nobel Prize in Chemistry

Lewis’s Cube I 1869 - Mendeleev’s Periodic Table Gilbert N. Lewis (1875-1946) 1897 - Thomson Discovers the Electron 1902 - Lewis’s Cubic Model of the Atom (Covalence) 1916 - Lewis Dot Formula Lewis was unsuccessful with the cubic model.

Lewis’s Cube II 1902 1916 1902 1916

Failure of the Cubic Model Single bond (Cl2) Edge Double bond (O2) Face Triple bond (N2) Cube within a cube?

Quantum Mechanics Quantum Mechanics leads to ... Resonance Hybridization Molecular Orbital Theory Pauling/The End Linus Pauling (1901 - 1994) The Nature of the Chemical Bond (1939)

The End The End