Practice Exam #1 Chemistry 5.12 Organic Chemistry • Midterm exam #1 will be held on Friday, February 21, from 12-1pm. • Notes and calculators will not be allowed in the exam. • You will be free to use molecular models during the exam. • You will be given a periodic table. • The exam will cover reading (Ch. 1, 2, 3.1-3.9) and lecture material through Tuesday, February 18. • Dr. Tabacco will give a review session at 7pm on Tuesday, February 18 • Additional suggested problems from the book (some of these were already suggested during lecture): 1-23,25,27,34,36,37,39-43, 45-47, 2-27- 31,33, 3-34,35,38,39,41a,b,42. • For best results, take this test as if it were your exam. That way, you'll know which areas need extra work before you get to the real exam. ANSWER KEY 1. Circle the correct answer. a) What is the approximate H-C-H bond angle in methane? 109° 120° 180° b) What is the IUPAC name for isobutane? isopropylmethane 3-methylbutane 2-methylpropane c) How much is a gauche butane interaction worth? 1.3 kcal/mol 0.9 kcal/mol 4.0 kcal/mol d) What is the barrier to rotation of ethane? 1.0 kcal/mol 1.3 kcal/mol 3.0 kcal/mol e) What is the PK, of ethane? 4.5 50 15.7 2. a) Provide line drawings for the following compounds. b) How many degrees of unsaturation does each compound have? methylcyclopentane phenol OH d.o.u. I d.0.4.4 5-tert-butyl-4-ethyl-2,3,4,7-tetramethyloctane Name Key 2 3. Below is a line drawing of beryllium chloride (BeCl2). a) Draw in all of the lone pairs. b) Label the atoms with their appropriate hybridization. c) What is the bond angle in BeCl₂? sp sp ↓ sp 3 Ci-Be-CI: 180° (linear) d) Draw an orbital picture of BeCl, Label all orbitals (bonding and non- bonding). Py 3 P e) Would you expect BeCl₂ to be nucleophilic or electrophilic? Explain briefly. Electrophilic. and two electrons. Be has four valence electrons. empty orbitals. It can accept Name Kery 3 4. For each pair, circle the molecule with the lowest pK_a, and provide a brief explanation for your choice. H-C-Cl (more EWGs → lower pK_a) vs H-C-H (inductive effects) vs (resonance)