11: Intro Organic Structures

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Organic Molecules

Structural Representations and Nomenclature

Many compounds contain at least one carbon-carbon bond (and often many others), usually many hydrogens, and possibly nitrogen, oxygen or a halogen. Because they can be fairly large and complex, a shorthand method for drawing has developed. It is important to be able to interpret such pictures.

Fill in the missing information in the table below:

Constitutional Isomers

These are constitutional isomers, compounds with the same molecular formula but different structures.

Complete the following table by writing in the missing molecular formulas.
What do the molecules have in common?
What don’t the molecules have in common?
Draw 3 constitutional isomers for the molecular formula C6H14 using skeletal representations. (Challenge: there are 5 isomers for C6H14. Can you draw them all?)

Common Functional Groups

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Flowchart for Identification of Common Functional Groups

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Part I. Identify the main functional group in the following structures:

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Part II. Identify each functional group circled in the following structures:

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Nomenclature of Hydrocarbons

Part 1. Straight Chain Alkanes

All alkane names have a prefix telling how many carbons are in the longest chain, and the suffix "ane", meaning alkane.

Prefixes: meth=1carbon; eth=2; prop=3; but=4; pent=5;hex=6; hept=7; oct = 8; non = 9; dec = 10.

Fill in the missing information in the table below:

Part 2. Branched Alkanes

For branched alkanes, the longest chain will get the root name.

Example:

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Find the longest chain for this structure:

Other carbons are treated as substituents with a –yl suffix. The substituent on this structure has one carbon so it will be a methyl. You must also indicate where the substituent is attached to the root structure.

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Fill in the missing information in the table below:
Complete the blanks when there are multiple branches.

Part 3. Cycloalkanes

Rings have the additional prefix, "cyclo".

Fill in the missing information in the table below:

Part 4. Alkenes and Alkynes

Alkene names have a prefix telling how many carbons are in the chain.

The suffix "ene", meaning alkene. Alkynes end in "yne".

A number indicates where in the chain the multiple bond can be found.

Fill in the missing information in the table below:

Part 5. Aromatic Rings

A very common grouping of atoms is the benzene ring, C6H6. The first two structures are equivalent by resonance. The third picture is yet another way to show the same structure and is simply an attempt to merge the first two. One or more of the H’s can be replaced with other atoms to connect the ring to a larger structure.

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The root on these names will be benzene.

Fill in the missing information below:

Name these aromatics: