CHEM 2311 Practice Exam 2 Fall 2014 1. Consider that C-O double bonds are shorter than C-O single bonds. Structural analysis of the molecule below reveals that some of its C-O bonds are of intermediate length (in between C-O single and C-O double bonds). Explain this observation using resonance structures. 2. The molecule shown to the right is called allene. a) How many sigma bonds does C-1 have_______? How many pi bonds_______? b) How many sigma bonds does C-2 have_______? How many pi bonds_______? c) What is the hybridization of C-1________? C-2________? 3. Show the products that form in the equilibrium between acetic acid (CH3CO2H) and sodium ethoxide (CH3CH2ONa). The equilibrium lies towards the (circle one): A. Starting materials B. Products 4. Methane has a pKa of about 50. Nitromethane has a pKa of 17.2 and is easily deprotonated by most strong bases. Show the conjugate base of nitromethane and explain why its pKa is lower than methane using resonance structures. C1C2C3H HHH5. Show the Newman projections of cis-1,3-dimethylcyclohexane in the lowest and highest energy conformations. What type(s) of strain lead(s) to an increase in energy for the highest energy conformation? Type(s) of strain:___________________________________________ 6. Consider the reaction below. Draw the three-dimensional structural formulas for the starting material and product. Boron has a formal charge of zero in the starting material; take this into account when drawing the structure for the product. What is the hybridization state of boron in the starting material? ____________ What is the hybridization state of boron in the product? ____________7. Draw the Newman projections for all of the staggered and eclipsed conformations of 1-bromopropane along the C1-C2 bond. Draw the potential energy diagram and start with the lowest energy conformation at 0o. (Hint: fix one end and then rotate the other end). Newman projections: Potential energy
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