UNIT 3 – ORGANIC

CHEMISTRY

OBJECTIVES

What does Organic mean?

• Is “organic” always good? (or better?)

• Organic chemistry is defined as the study of compounds in which carbon is the principle element. Organic compounds always contain a combination of carbon and hydrogen. They may also contain oxygen and nitrogen.

MOST…

• Carbon based compounds are organic…• DNA, protein, carbohydrates, fats, hydrocarbons, alcohols,

aromatics…

• EXCEPT:

• Carbonates (CO32-)

• Carbon Monoxide (CO) and Carbon Dioxide (CO2)

The Carbon Atom

• What is so special about carbon that makes it able to form so many different compounds• Can form four covalent bonds

• Can bond to any element on the periodic table

• Forms strong single, double, and triple bonds with other carbon atoms

• Single = 1 shared pair of e-

• Double = 2

• Triple = 3

• Organic compounds are held together by covalent bonds.

• Every carbon atom will have FOUR lines around it but these lines will not always be single lines. This is because carbon atoms don’t always form single covalent bonds. Double or triple bonds can form between the carbon atoms.

• Can also forms rings and chains of various shapes and sizes

• Double and triple bonds change the structure of the geometry around the ‘central carbon’

• Structure dictates the molecule’s properties

Saturated vs. Unsaturated Carbons

• Saturated: molecules with only single bonds, generally stable and unreactive

• Unsaturated: molecules with double or triple bonds, more reactive and less stable

Complete vs. Condensed vs. Line Diagrams

• Complete:

• Condensed:

• Line:

Molecular Shape and Polarity

• Polar covalent bond: covalent bond between two atoms with different electronegativities

• Electronegativity: measure of how strongly an atom attracts electrons in a chemical bond• Every polar bond has a bond dipole

HYDROCARBONS

• Hydrocarbons are a group of organic compounds that contain ONLY carbon and hydrogen.

• Hydrocarbons are classified into three different groups according to whether the molecules contain only single bonds between the carbon atoms, or some double or triple bonds between the carbon atoms.

Types of Hydrocarbons

• Aliphatic: carbon atoms are bonded in chains or rings

• Aromatic: based on the compound benzene

• Classified into three categories: alkanes, alkenes, and alkynes

• Functional groups: reactive group of bonded atoms that are members of the same chemical family and similar chemical properties (i.e. double and triple bonds)

ALKANES

• Alkanes are hydrocarbons that contain only single bonds between the carbon atoms. The general formula for an alkane is CnH2n + 2.

ALKENES

• Alkenes are hydrocarbons that contain at least one carbon to carbon double bond in the molecules. The general formula for an alkene with one double bond in the molecule is CnH2n.

ALKYNES

• Alkynes are hydrocarbons that contain at least one carbon to carbon triple bond in the molecule. The general formula for an alkyne with one triple bond in the molecule is CnH2n-2.

NAMING HYDROCARBONS

• … and you thought you were done with naming compounds

Naming hydrocarbons

• The systematic name of hydrocarbons will have two parts. The first part of the name indicates the number of carbon atoms in the chain. The ending of each name indicates the type of hydrocarbon.

- ane – alkane – all single bonds

- ene – alkene – at least one double bond

- yne – alkyne – at least one triple bond

These prefixes must be memorized.

Prefixes for side chains

• If there are branches present on the chain, then the branches are called alkyl groups• The suffix to these is “-yl” but the root is still the same

• Example: methyl = CH3 (root = 1 carbon)

• Give the prefix the lowest number for double and triple bonds

Naming Hydrocarbons

1. Find the root

2. Find the suffix

3. Give the position numbers

4. Find the prefix

5. Put it all together

Example 1:1. Propane is a fuel that is commonly used in gas barbecues. Draw a structural

formula for propane, and write its formula.

2. Butane, commonly used in lighters, contains a four-carbon chain joined by single bonds.

3. Octane, found in gasoline, contains an eight-carbon chain joined by single bonds.

4. Methane, the natural gas that is used in homes and school science labs, is a single carbon atom with four hydrogen atoms.

Drawing Structural Formulas for Alkenes and Alkynes

• Draw a structural formula and write the molecular formula for 1-hexene.• Step 1: Write Carbon Backbone of Appropriate Length

• Start with the name “hexene.” The hex- tells you that there are six C atoms in a chain.

Draw a structural formula and write the molecular formula for 1-hexene

• Step 2: Establish Location of Double Bond• The -ene tells you that there is a double bond linking two of the C

atoms

• The number at the beginning of the name tells you which C atom starts the double bond.

• Since the alkene is 1-hexene, the double bond starts at the first C atom and ends at the second C atom.

Draw a structural formula and write the molecular formula for 1-hexene

• Step 3: Fill Remaining Bonds with Hydrogen Atoms

• There are 6 C atoms and 12 H atoms in total, so the molecular formula is C6H12

Write the IUPAC name and the molecular formula for each of the followingalkenes:

Draw a structural formula and write the molecular formula for each of the following hydrocarbons:

• (a) ethene

• (b) ethyne

• (c) 2-hexene

Properties of Hydrocarbons

• Non-polar molecules

• Do not dissolve in water

• Low melting/boiling points, BUT increase as you add more carbons

Assignment

• Worksheet