Introduction to Organic Chemistry Mir Ishruna Muniyat

What’s Organic About Organic Chemistry? Mid 18th Century - Compounds produced by living things were recognized as more difficult to isolate, purify and handle than compounds obtained from inanimate minerals. 1770 - Torbern Berman (Swedish chemist) noted the difference between chemicals derived from organic (living) and from inorganic (mineral) substances. Organic chemicals came to mean chemicals derived from living organisms.

The Vital Force Theory of Organic Chemistry Late 18th and early 19th Centuries - Many chemists believed that a “vital force”, a mysterious, presumed property of living things was needed for the formation of organic compounds. This theory held that in the absence of this “vital force” of living things, no organic compounds could be formed. But . . .

..Chevreul's Soap! 1816 - Michel Chevreul (French chemist) converted soap (prepared from animal fat and therefore organic) into glycerol and substances he called fatty acids Since these were also classified as organic compounds, Chevreul converted one organic compound into other organic compounds WITHOUT intervention of the vital force!!

Wohler’s Synthesis of Urea In 1828 Friedrich Wohler (German chemist) converted ammonium cyanate, recognized as an inorganic compound, into urea, an organic compound found in human urine. Wohler’s laboratory synthesis of urea from ammonium cyanate dealt a mortal blow to the vital force theory of organic chemistry. 1800-1882 In a laboratory!

Summery of Theories.. Vital force – ‘vitalism’: A mysterious, presumed property of living things… Friedrich Wohler overthrew vitalism. Synthesis of urea from ammonium cyanate Distinguishing feature: organic compounds all contain the CARBON atom

Why Study Organic Chemistry?

What is ORGANIC CHEMISTRY?

It is… The Chemistry of Carbon Compounds. Because almost all chemical compounds found in living systems contain carbon, today we recognize organic chemistry as the chemistry of carbon compounds. (One vital compound, common to all living things, contains no carbon at all. Which compound is that?)

Other elements in organic compounds: H, O, N, S, P, Cl, Br, I and other transition metals Why Carbon?

Ans: Versatility! Carbon- Can share four valence electrons Form strong covalent bonds Form rings and long chains, e.g. benzene and DNA

Some common terms… Ionic compounds: compounds made up of a metal cation and a nonmetal anion e.g. NaCl, KNO3 Intramolecular forces of attraction: forces existing within molecules that holds the atoms together e.g. Ionic bond, covalent bond, metallic bond Intermolecular forces of attraction: forces existing between molecules

Intermolecular Forces of Attraction Ion-dipole Between an ionic compound and a polar compound e.g. NaCl dissolved in water Dipole-dipole Between two polar compounds e.g. HCl dissolved in water

London dispersion forces/van der Waals forces Hydrogen Bonding Requirement: H atoms bonded to F, O, N Strongest intermolecular force e.g. NH3 in H2O London dispersion forces/van der Waals forces Between two NONPOLAR compounds Due to uneven electron distribution Temporary Dipole Weakest intermolecular force; present in all organic molecules

The larger the size of the organic compound, the larger the London dispersion forces.

Properties of Organic Compounds Solubility relies on the intermolecular forces of organic compounds ‘like dissolves like’ Polar solvents dissolve in polar solutes. Nonpolar solvents dissolve in nonpolar solutes. Organic compounds = mostly nonpolar It only follows that most organic compounds are soluble in organic solvents.

Naphthalene in water Naphthalene in ether No ionic bonds, just pure London dispersion forces Naphthalene in water Water is capable of hydrogen bonding; naphthalene is not.

Electrical Conductivity Electrical conductivity is only possible when a compound contains charged particles (i.e. an electrolyte) e.g. NaCl, NaNO3 are electrolytes Since most organic compounds are not ionic, it does not conduct electricity.

sucrose ethanol NaCl hexane

Flammable Ethanol Due to the C-C bond energies in organic compounds Energy released is in the form of heat Ethanol Ethanol – produces the distinct blue flame

Charring Sucrose also known as burning, scorching organic compounds are sensitive to heat End result of charring: elemental C Sucrose disaccharide common ingredient in sweet foods like ice cream, candy also works as a food preservative

IMF of sucrose: London dispersion force Remember always: Intramolecular forces are way STRONGER than intermolecular forces.

Summary Organic chemistry is the study of carbon compounds. Organic compounds have the following properties: Flammable Combustible Immiscible in polar solvents like water Non-electrolytes; do not conduct electricity