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SCH4U - Introduction to

Organic Chemistry*S*T*A*R*R*I*N*G*

The ALKANESThe ALKENES

The ALKYL GroupsThe Aromatic Compounds

And all Their Little ISOMERS !

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And Co-Starring

*S T R U C T U R E S*and

F o r m u l a s

With special mention toThe International Union of Pure

and Applied Chemistry

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Structural Features of Carbon Compounds

• The compound may be open-chained or cyclic.• Chains may be straight or branched.• May be saturated or unsaturated.• Rings can be carbocyclic or heterocyclic.

• You will be dealing with ALL these cases at one time or another in this class!

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Structures and Chemical Formulas • Molecular formulas are only useful for the very

simplest compounds such as CH4 or C2H6, since they give no information on how atoms connect.

• There is usually more than one way to arrange the atoms listed in the molecular formula

• Expanded molecular formulas show atoms in the order that they appear, with brackets to indicate groups attached to chains.

– ie) CH3C(CH3)2CH2CH3

More ways to represent...

Organic compounds can be very complex! • A system is needed that shows structure.

Skeleton structuresExpanded structures (full structural formulas)Condensed structural formulasLine representations

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Skeleton Structures• Skeleton structure or skeleton formula

• Leaves out the hydrogen atoms.• For hydrocarbons, only the carbon skeleton and connecting bonds are

shown.• Bonds are represented as lines. .

• C – Example: Isobutane C-C-C

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Expanded Structural Formulas

• Expanded structural formula• Shows all atoms with bonds.• Bonds are represented as lines

– Example Isobutane

• Also called a full structural formula.

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Condensed Formulas

• Condensed formula• Shorthand way of writing formula.• Lists all atoms in order and tells how they are bound together.• C-H bonds are assumed, not shown– Example: Isobutane

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Line Structural Diagrams

• Line formula or line representation• The end of each line or meeting point represents a carbon atom• Hydrogen not shown, assumed• Zig zag pattern for single and double bonds, triple bonds are in

straight line• Example: Isobutane

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Isomers• Structural Isomers: Compounds with the same

number of atoms and bonds but with different arrangements.– CH3CH2CH2CH2CH3 CH3CH(CH3)CH2CH3 (CH3)4C

Geometric IsomersCompounds which have the SAME molecular formula, but different arrangements of atoms around a double carbon-carbon bond

• These exist when two or more arrangements are possible due to the type of bond.

• Alkanes - can rotate about all bonds– no geometric isomers

• Alkenes - rigid bond– can have geometric isomers

• Alkynes - rigid bond but linear– no geometric isomers

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Geometric Isomers (continued)

There are two possible arrangements

Example 2-butene

C=CH

CH3

H3C

HC=C

CH3

HH

H3C

cis Two methyl groups areon the same side (and

so are the two H’s.

transTwo methyl groups

are on opposite sides.