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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*

andF 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.