Lab Activity 4: Structures and Properties of Aliphatic Compounds

Transcription

1 Chemistry 2202 Structures and Properties of Aliphatic Compounds Page 1 of 6 Lab Activity 4: Structures and Properties of Aliphatic Compounds Introduction Aliphatic compounds are hydrocarbons that have carbon-carbon bonds that can be either: single, double or triple. In this lab, you will make predictions about the shapes and properties of various aliphatic compounds, and then build models and do research to verify your predictions. Textbook Readings MHR Chemistry Section 9.2: Representing Hydrocarbons pages Section 9.3: Classifying Hydrocarbons pages ; ; Problem How are the properties of aliphatic hydrocarbons related to their structure? Pre-Lab Assignment 1. Complete the table below. Note: every row should result in a different molecule. Draw the type of diagram indicated in brackets while completing column 3.

2 Chemistry 2202 Structures and Properties of Aliphatic Compounds Page 2 of 6 Name(s): School: Name Formula Structural Diagram 1a. pentane (condensed) b. methylbutane (skeleton) c. dimethylpropane (line) 2a. C 4 H 8 (complete) (noncyclic) b. C 4 H 8 (sketeton) (noncyclic) c. C 4 H 8 (condensed) (noncyclic) d. C 4 H 8 (line) (cyclic) 3a. C 4 H 6 (noncyclic) (skeleton) Make a compound you can name! b. C 4 H 6 (line) (cyclic)

3 Chemistry 2202 Structures and Properties of Aliphatic Compounds Page 3 of 6 Materials per pair of students: one molecular model kit or one ACD Chemsketch/3D viewer software on your computer Safety 1. Be careful when inserting springs into the balls. Twist the spring onto and off of the ball to prevent damage to the spring. 2. Wear eye protection because the springs sometimes come loose and become flying projectiles. Procedure: 1. Construct models of the hydrocarbons from your pre-lab table using either a molecular model kit or ACD Chemsketch/3D viewer on your computer. If using a molecular model kit, follow these guidelines: carbon: black balls hydrogen: yellow or white balls (1 hole) single bonds: wooden sticks (Note: you will have to use springs for the single bonds in the cyclic molecules. (2d, 3b)) double (two springs), triple (three springs) or bonds in cyclic compounds If using ACD Chemsketch/3D viewer software, use these guidelines: Generate a condensed diagram in ChemSketch first by clicking in the whiteboard to add the first carbon, then positioning your mouse over the carbon you are adding on to and clicking again. To make a double or triple bond, position your mouse over the bond and click once to make a double bond, twice to make a triple bond. Transfer the condensed diagram into 3D viewer by clicking on ACD/Labs in the menu bar, then selecting 3D viewer. Once you have loaded the viewer, you can switch from ChemSketch to 3D View using the tabs at the bottom left of your screen. To get the correct shape and view of your molecule, select the "Balls and Sticks" view from the toolbar, and select "3D Optimization" from the toolbar. 2. Note the type of bonding around each carbon atom in your molecules (single, double, triple), and note the resulting shape in the Results table below.

4 Chemistry 2202 Structures and Properties of Aliphatic Compounds Page 4 of 6 3. Save the images of the molecules. If using a molecular model kit: Write the name of each molecule on a separate piece of paper or paper towel as a label. Lay the model on the paper. If possible, group the isomers together (ie, 1 a c; 2 a - d, 3 a b). Take a picture of your model or groups of models with a digital camera and up-load these images with your formal lab write-up. If using ACD Chemsketch/3D viewer software: In the 3D Viewer screen, print each molecule to a.pdf file. If the printer is not set up to print to.pdf, change the printer by clicking on File > Printer Setup and selecting Adobe PDF. Save each model by its number on the pre-lab table. Open up 1a.pdf, 1b.pdf, 1c.pdf at the same time. Merge these files by clicking on the page tab on the left, and dragging all of the pages from the three separate files into one file. Save as 1.pdf. Repeat the last step by loading all of the.pdf files from number 2 and 3 of the pre-lab table, merging them into one file, and saving as 2.pdf and 3.pdf respectively. Upload the three.pdf files with your images of your molecules with your formal lab write-up.

5 Chemistry 2202 Structures and Properties of Aliphatic Compounds Page 5 of 6 Name(s): School: Results From the models you built, fill in the below: Shape around Carbon: Type of Bonding around Carbon: (Tetrahedral, v-shaped, trigonal planar, linear, or pyramidal) A carbon making 4 single bonds A carbon making two single and one double bond A carbon making two double bonds A carbon making one triple and one single bond Analysis: 1. The boiling points of the isomers of C 5 H 12 (compounds 1 a - c in the pre-lab table) are, in no particular order: 9.5 C, 27.8 C and 36.1 C. Match each isomer with a boiling point and explain your reasoning. Include an intermolecular force analysis in your answer.. (Internet search may prove helpful here!)

6 Chemistry 2202 Structures and Properties of Aliphatic Compounds Page 6 of 6 Name(s): School: 2. Which of the three non-cyclic isomers of C 4 H 8 would you expect to have the lowest surface tension? Justify your answer with an intermolecular forces analysis. 3. Which of the non-cyclic isomers of C 4 H 8 (compounds 2 a - c in the table above) can form cis and trans isomers? Draw and label each geometric isomer as either cis or trans. 4. Name a solvent that the isomers of C 4 H 6 (molecules 3 a b) would be soluble in, and explain your reasoning. Conclusion In your conclusion, comment on the similarities and differences in properties of substances that have the same molecular formulas, but different structures.