An Introduction to Organic Chemistry

Orgins Originally defined as the chemistry of living materials or originating from living sources Wohler synthesized urea from non organic sources Now generally defined as the chemistry of carbon and its compounds

Carbon is Unique More than 90% of all known compounds are carbon compounds and therefore organic Living systems are all carbon based Carbon has unique characteristics that make multiple compounds possible

Hydrocarbons Hydrocarbons are organic compounds that are made up of only carbon and hydrogen. There are several different categories of hydrocarbons including: –Alkanes –Alkenes –Alkynes –Cyclic Hydrocarbons –Aromatic hydrocarbons

Homologous Series Compounds that have the same general formula but differing lengths of carbon chains form a homologous series

Homologous Series: Ex 1 A homologous series of alkanes CH 4 Methane C2H6C2H6 Ethane C3H8C3H8 Propane C 4 H 10 Butane C 5 H 12 Pentane Each compound in this series differs from the previous compound by a –CH 2 – The general formula for these compounds could be written as C n H 2n+2

Homologous Series: Ex 2 A homologous series of alkenes C2H4C2H4 Ethene C3H6C3H6 Propene C4H8C4H8 1-Butene C 5 H 10 1-Pentene Each compound in this series differs from the previous compound by a –CH 2 – The general formula for these compounds could be written as C n H 2n

Homologous Series: Ex 3 A homologous series of alcohols CH 4 OH Methanol C 2 H 6 OH Ethanol C 3 H 8 OH 1-Propanol C 4 H 10 OH 1-Butanol C 5 H 12 OH 1-Pentanol Each compound in this series differs from the previous compound by a –CH 2 – The general formula for these compounds could be written as C n H 2n+1 OH

Classifying Organic Compounds Many configurations of carbon atoms are possible in a molecule Empirical and molecular formulas are the same for many different compounds The relative locations of various combinations of atoms in a formula is very important Structural formulas show the location and bonding pattern for each atom in a formula

Structural Formulas & Structural Isomers The two molecules below both have the same empirical and molecular formulas but they have very different characteristics. They are structural isomers and are considered different compounds.

Functional Groups AlcoholR- OH Aldehyde Ketone Ether

Functional Groups Carboxylic Acid Amide Amine Amino acid

Functional Groups Ester Thiol-S-HR- SHCH 3 CH 2 -SH Benzene ring

Functional Groups  Many larger molecules have more than one functional group.

Functional Groups  The physical and chemical properties of organic compounds are related to their functional groups.  Compounds may have different numbers of carbon atoms but the same functional group(s) will often have similar properties.

Physical Properties of Organic Compounds Boiling points of organic compounds reflects the strength of the intermolecular attractive forces that hold the molecules of a substance together in a condensed phase Organic compounds typically melt and boil at much lower temperatures than most inorganic compounds. The melting and boiling points correlate with the polarity of the molecules and their molecular mass 16

Physical Properties of Organic Compounds Boiling Point Trends The melting points and boiling points of most organic compounds increase with increasing molecular mass 17

Physical Properties of Organic Compounds The boiling points of most organic compounds increase with increasing molecular polarity. The above compounds have similar molar masses, but their boiling points vary considerably. 18

Solubility of Organic Compounds The solubility of organic compounds in water depends on the polarity of any attached functional groups. Nonpolar organic compounds are hydrophobic, so, they are less soluble in water than in organic solvents. Organic compounds that contain polar groups such as low molecular weight alcohols and others dissolve in water. They are sufficiently polar for hydrogen bonding to occur. 19

Organic Solvents Organic compounds tend to dissolve in a variety of organic solvents. These solvents can be either pure substances like acetone or ethyl alcohol, or mixtures such as petroleum ether. The solubility of organic compounds in these different solvents depends upon the type of solvent and in particular the functional groups if present. As the molar mass of organic compounds increases the compound becomes more hydrophobic. 20