chemistry cast study

Case Study #2

Organic Line-angle Structures, Isomers, and Molecular Models

Skills we are working on in this case study on organic molecules are:

1. Reading, Writing and interpreting skeletal representations of organic molecules.

The skeletal representation shows only the C-C bonds, but none of the C or H atoms. They are understood based on the octet rule (i.e., 4 bonds to every carbon atom).

2. Learning and working with constitutional isomers (i.e., the same empirical formula, but different points of attachment).

3. Building a 3-D tetrahedral model of methane.

4. Building models of methane, ethane, propane, n-butane and isobutane.

Constitutional Isomers

Critical Thinking Questions

1. Draw a line-bond representation of the molecule below shown as a skeletal representation. Also, write its molecular formula.

2. In skeletal representations the hydrogens are not shown. Is it still possible to tell how many hydrogens there are on a particular carbon? Explain how.

3. Complete the table in Model 2 by writing in the molecular formula.

4. What do the molecules in a given column (1 or 2 above) have in common with the other molecules in that column?

5. What do the molecules in a given column NOT have in common with the other molecules in that column?

6. All the structures in a given column are constitutional isomers of one another, but the structures in column 1 are not constitutional isomers of structures in column 2. Based in this information, write a definition for the term constitutional isomers.

7. Below is a 2-D representation of methane, CH4. Its 3-D shape is a

tetrahedron. Using the large marshmallows as carbon atoms, small marshmallows as hydrogen atoms and toothpicks as the covalent C-H bonds, build a model of methane.

8. The homolytic cleavage of a C-H bond results in hydrogen and methyl

______ _________. When two methyl ____________ combine forming a C-C bond,

ethane is formed. Build a model of ethane.

9. Removing a hydrogen atom from ethane and replacing it with a methyl group

results in ______________, C3H8. Build a model of C3H8.

10. Replace a 1o (primary) hydrogen with a methyl group to make ____________.

Replace a 2o (secondary) hydrogen with a methyl group to make ______________.

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