info_241_lab_reports - Lab#1 Molecular Models The purpose...

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1 Lab #1: Molecular Models The purpose of this lab is to help you visualize the three-dimensional structure of organic molecules using molecular models. You will study conformational analysis and stereochemistry of acyclic alkanes and cyclohexane. Before the lab you should review the sections in your organic textbook and answer the pre- lab questions in your notebook. The molecular model kit contains plastic balls and sticks to represent atoms and bonds. The black balls with 4 holes represent carbons, the white balls represent hydrogen, and the colored balls represent other atoms, such as nitrogen, oxygen or the halogens. Joining the balls together with gray sticks depicts a bond between two atoms. (The longer gray sticks are used in the formation of double and triple bonds.) Pre-lab Questions (0.5 pts. Each) Give a clear, concise definition for each of the following terms. Be specific. Photocopy the page from your notebook and hand in to the TA before beginning the exercises. (Put your name and the date at the top of the page.) 1. Isomers: 2. Conformations: 3. Chiral: 4. Stereoisomers: 5. Enantiomers: 6. Diastereomers: Equipment Each pair of students will check out one model kit from the organic chemistry stockroom (Bagley 271). Of course, you can use your own if you have one. Procedures Partners should take turns building the models so that each student gets hands-on practice. Answer the questions about each model on the worksheet and hand it in to your TA at the end of the lab period. Each part is worth 0.5 points . There is no additional report for this lab.
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2 Exercise 1: Conformational Analysis of Alkanes 1. Construct a model of ethane (CH 3 CH 3 ) by joining two carbon atoms with a single bond and then attaching three hydrogens to each of the carbon atoms. Sight down the carbon-carbon bond and rotate one carbon until all the hydrogens of one carbon atom are directly behind the hydrogens of the other carbon. This is referred to as the eclipsed conformation. a) Draw both the Newman projection and the sawhorse (using wedges and dashes) for the eclipsed conformation. b) Rotate one of the carbon atoms about the single bond by 60° with respect to the other carbon. This is referred to as the staggered conformation. Draw both the Newman projection and the sawhorse (using wedges and dashes) for the staggered conformation. c) Which conformation is higher energy? Explain why in one sentence. 2. Construct a model of butane (CH 3 CH 2 CH 2 CH 3 ) and arrange it in a fully staggered conformation (such that the two methyl groups are 180° from each other). This is called the anti conformation. a) Draw the Newman projection for the anti conformation, sighting down the C2- C3 bond. b)
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info_241_lab_reports - Lab#1 Molecular Models The purpose...

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