Review 1 Weekly Review Lecture Chem S‐20ab Welcome to the first weekly review lecture. This handout is split into two parts. First, there’s a list of stuff you need to be able to do for the exam. Following that, there is a bunch of problems. We will not be able to get through all the problems, but we’ll do our best. Answers for ALL of these problems (whether we get to them or not) will be posted to the website after the review. Let’s see how much ground we can cover . . . Fundamentals: You should be able to . . . 1) Draw Lewis structures. 2) Draw and evaluate resonance structures. 3) Identify the hybridization and geometry of all atoms in a molecule. 4) Convert between Lewis structures and skeletal structures. 5) Name alkanes and alkenes, including the E/Z convention. 6) Draw Newman projections and compare stability of conformations. 7) Identify the functional groups on p. 14 of the purple book. 8) Draw a complete MO diagram for a given molecule. 9) Identify the HOMO and LUMO of a given molecule. 10) Use the HOMO and LUMO to predict the single‐step reaction between two molecules. 11) Draw curved arrows to go from reactants to products in a single reaction step. 12) Draw the products that would result from a given set of curved arrows. 13) Explain the relative acidity of protons using: electronegativity, hybridization, resonance, and charge. 14) Know the pKa values for the functional groups on p. 28 of the purple book. 15) Find the Keq of an acid/base reaction using pKa values. Alkenes: You should be able to . . . 1) Explain the differences in stability among carbocations. 2) Predict alkyl shifts of carbocations that can become more stable a. Primary  secondary or secondary  tertiary b. Relieving ring strain of 3‐ or 4‐membered ring 3) Draw the mechanism that results in a given product. This may be a product you could not have predicted, but you should use your knowledge of mechanisms to figure it out. 4) Know all 4 pieces of the “reaction chart” for the following reactions. That means being able to predict the starting materials, products, or reagents. You need to know the mechanisms for all reactions EXCEPT those marked with an *. a. Alkene + HCl or HBr b. Alkene + H2O, H+ c. Alkene + ROH, H+ d. Alkene + X2 e. Alkene + X2 + H2O f. Alkene + X2 + ROH g. *Alkene + H2, Pt/C h. Alkene + HBr, peroxides i. Hydroboration/oxidation of an alkene *(no need to know mech. for H2O2 step) j. Oxymercuration/reduction of an alkene with water *(no need to know mech. for NaBH4 step) k. Alkoxymercuration/reduction of an alkene with ROH *(no need to know mech. for NaBH4 step) l. *Ozonolysis of alkene with Me2S workup m. *Ozonolysis of alkene with H2O2 workup Review 1 Weekly Review Lecture Chem S‐20ab Problems: 1) Draw a complete Lewis structure for each molecule below, including all lone pairs. Then draw the best alternate resonance structure for the molecule, and decide which structure is more stable. a. OCN‐ b. NNO c.
2) Identify the functional groups in the molecule below, and give hybridizations for the circled atoms. How do you think one would go about naming this monstrosity? N
H
H
H
N
H
O
CN
O
3) Provide the best systematic name for the following molecule: 4) Draw the structure of (Z)‐6‐tert‐butyl‐4‐isopropyl‐3‐methyl‐3‐nonene. 5) Consider the conformations obtained for the following molecule by rotation around the C‐C bond: Interaction
Energy (kcal/mol)
Eclipsed Cl / Cl
2.8
Eclipsed Cl/ H
1.4
Eclipsed H / H
1.0
Gauche Cl / Cl
1.0
a) This molecule is expected to have a single lowest‐energy conformation. Using a Newman projection, show the lowest‐energy conformation of this molecule. Be sure to view the molecule along the C—C bond. b) This molecule is also expected to have a single highest‐energy conformation. Using a Newman projection, show the highest‐energy conformation of this molecule. c) Using the table of interaction energies given on the right, calculate the energy difference between the highest‐ and lowest‐energy conformers of this molecule. Review 1 Weekly Review Lecture Chem S‐20ab 6) Consider the following two molecules: Molecule A: Molecule B: a. For each molecule, provide a complete Molecular Orbital diagram showing the energies of the valence orbitals in the molecule. Label each orbital with an appropriate label (, , , , or nonbonding), and fill each orbital with the appropriate number of electrons. b. Using curved arrows, show the result of a single‐step reaction between these two molecules. Draw in the product that would result from this single step. 7) For each of the molecules shown below, consider 8) Each of the following shows one step in a reaction mechanism. Draw the product(s) that would result from the indicated curved arrows. 9) Each of the following shows a single reaction step. Show the curved arrows required to get from the reactants to the products. O
O
+ Br
Br
10) In each of the following molecules, determine which of the shown protons is more acidic. Justify your choice. Review 1 Weekly Review Lecture Chem S‐20ab 11) The following compound, called a sulfonamide, undergoes an acid‐base reaction as shown below. Draw the structures of the conjugate acid and base for the reaction, and calculate the value of the equilibrium constant for the acid‐base reaction. O O
S
NH 2
Keq = ?
NH2
+
pKa ~16
12) Provide a complete curved‐arrow mechanism for the following transformation. For each step, identify the frontier molecular orbitals involved. EtOH, H+
O
13) The alkene below can form 4 different products with an alcohol group, depending on the reagents used. Predict the product when this alkene is subjected to the conditions shown. Explain the differences. 14) Synthesize the following molecules starting from any hydrocarbons with 4 or fewer carbons. 15) Alkenes are known to react with CH3SH by a radical mechanism in the presence of peroxides (ROOR). a. Propose a mechanism for the following reaction. b. Why is the other isomer, shown below, not formed in the reaction? CH3
CH3
S