Organic Chemistry

Nathan Watson

Lincoln High School

Portland, OR

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 Characteristics

• Electron configuration 1s2 2s2 2p2

• Four valence electrons• Hybridization• Forms four bonds with other atoms

including other carbon atoms• Able to catenate – form chains and

rings• Able to form multiple bonds

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

Bonding in Ethane

• Sp3 hybridized orbitals

Bonding in ethene

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

CH4 Methane

C2H6 Ethane

C3H8 Propane

C4H10 Butane

C5H12 Pentane

• Each compound in this series differs from the previous compound by a –CH2 –

• The general formula for these compounds could be written as CnH2n+2

Homologous Series: Ex 2

A homologous series of alkenes

C2H4 Ethene

C3H6 Propene

C4H8 1-Butene

C5H10 1-Pentene

• Each compound in this series differs from the previous compound by a –CH2 –

• The general formula for these compounds could be written as CnH2n

Homologous Series: Ex 3

A homologous series of alcohols

CH4OH Methanol

C2H6OH Ethanol

C3H8OH 1-Propanol

C4H10OH 1-Butanol

C5H12OH 1-Pentanol

• Each compound in this series differs from the previous compound by a –CH2 –

• The general formula for these compounds could be written as CnH2n+1OH

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

• The two molecules below both have the same empirical and molecular formulas but they have very different characteristics. They are considered different compounds.

Functional Groups

Alcohol R- OH

Aldehyde

Ketone

Ether

Functional GroupsCarboxylic Acid

Amide

Amine

Amino acid

Functional GroupsEster

Thiol -S-H R- SH CH3CH2-SH

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

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Physical Properties of Organic Compounds

Boiling Point Trends

The melting points and boiling points of most organic compounds increase with increasing molecular mass

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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.

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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.

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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. 23

Alkanes

• Alkanes are hydrocarbons that have only C-C single bonds.

• Examples– Methane CH4

– Ethane CH3-CH3

– Propane CH3-CH2-CH3

– Butane CH3-CH2-CH2-CH3

– Pentane CH3-CH2-CH2-CH2-CH3