Chemistry 250 Stereochemistry Workshop

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Chemistry 250 Stereochemistry Workshop Name Lab Day TA Name Febraury 2013 Student # Lab Time Question 1 (5 min) A. Construct a model of t-butylcyclohexane in the chair form in which the methyl group is axial. Note that in this conformation there are unfavorable diaxial interactions. Ensure that you can identify these. B. Make a line-angle drawing for the above chair conformation to clearly depict that the t-butyl group is axial. C. Show the above model to your TA and the TA will show you how to flip the ring. Now you would note that when the t-butyl group is in the equatorial position there are no unfavorable diaxial interactions. D. Draw the above (from C) chair conformation in which the methyl group is shown as equatorial. 1 Chemistry 250 Stereochemistry Workshop Question 2 ( 6 min) Febraury 2013 Two cis-trans isomers exist for 1-bromo-3-methylcyclohexane; they are cis-1-bromo-3-methylcyclohexane and trans-1bromo-3-methylcyclohexane: Two different chair conformations (Conformation 1 and Conformation 2) of cyclohexane with carbon atoms numbered 1 – 6 are given below. For the cis-1,3-dimethylcyclohexane draw methyl groups at carbons 1 and 3 in each of its two possible conformations. (2 marks) In each conformation, indicate whether the methyl groups are axial or equatorial. Which of the two conformations is more stable? Conformation ___2___ is the more stable (1 mark) In a similar fashion, draw the two conformations for trans-1-bromo-3-methylcyclohexane. (2 marks) 2 Chemistry 250 Stereochemistry Workshop Febraury 2013 Question 3 (10 min) Build the model for 1,2-dimethoxyethane (CH3OCH2CH2OCH3). There are two staggered and two eclipsed conformation around the bond formed between C-1 and C-2. All four of these conformations have different stabilities. (HINT: Learn to simplify when building the models. For example, do not

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