Questions

Name _______________________________________ Instructor ____________________________________ Chem ____________ Section/Color ______________ EXPERIMENT: MOLECULAR MODELING I: CONFORMATIONS ANALYSIS & PROPERTIES Date ________________________________________ Laboratory Questions These questions are to be completed and turned in at the beginning of the pre-lab period. PRE-LAB QUESTIONS 1. Examine the diagram of conformational energies for butane shown in the McMurry textbook (Figure 3.9). Which conformation(s) would represent a local minimum and which would represent a global minimum? 2. McMurry indicates that the gauche conformation (60° dihedral angle) of butane results in steric strain because of repulsion between the two methyl groups (p 96). a. Explain why the magnitude of this steric strain would decrease if the dihedral angle was increased from 60° to 65° b. How would the magnitude of this steric strain between these two gauche methyl groups change (increase or decrease?) if the C 1 -C 2 -C 3 (or C 2 -C 3 -C 4 ) bond angle was increased to more than 109.5°? 3. Consider equation 1 below. (1) E strain = E stretch + E angle + E torsion + E steric a. How would E torsion change when the dihedral angle of gauche butane is increased from 60 o to 65 o ? Hint: Look at Figure 3.7 where the energy changes are a result of only torsional strain. b. How would E angle change if bond angles are increased as discussed in 2b? Name _______________________________________ Instructor ____________________________________ Chem ____________ Section/Color ______________ EXPERIMENT: MOLECULAR MODELING I: CONFORMATIONS ANALYSIS & PROPERTIES Date ________________________________________ Laboratory Questions These questions are to be completed and turned in with the Laboratory Report. POST-LAB QUESTIONS Post lab questions are in your laboratory manual. Microsoft Word - MolecularModelingI.doc