Massachusetts Institute of Technology Organic Chemistry 5.13 Friday, September 26, 2003 Prof. Timothy F. Jamison Hour Exam #1 Name OTHER ANSWERS POSSIBLE IN SOME SUGGESTED SOLUTIONS CASES PARTIAL CREDIT POSSIBLE IN (please both print and sign your name) MOST CASES, Official Recitation Instructor Directions: Closed book exam, no books, notebooks, notes, etc. allowed. However, calculators, rulers, and molecular model sets are permitted. Please read through the entire exam before beginning, in order to make sure that you have all the pages and in order to gauge the relative difficulty of each question. Budget your time accordingly. Show all of your work if you wish to receive partial credit. You should have 12 pages total: 6 exam pages including this page, 4 pages of reference information, and 2 blank pages for scratchwork. Question: Grader: 1. 36 points 2. 20 points 3. 20 points 4. 24 points Total: 100 points 1 1. (36 points total) Use the information provided below and the IR and NMR spectra on the next page to answer the following questions. a. (10 points) Determine the molecular formula that satisfies the following data (circle your final answer): EA (found): C, 37.02; H, 2.22; N, 18.50; and M = 227 CHN306 b. (6 points) Calculate the Index of Hydrogen Deficiency (IHD) for the molecule in a, above (circle your final answer). 7 c. (5 points) An IR spectrum of the molecule in a appears on the following page. What functional group or groups correspond(s) to the 2 most intense peaks in the spectrum? Draw the structure of this/these group(s), showing all bonds (i.e. single, double, triple). NITRO GROUPS d. (10 points) Using the information in a, b, and c, above, and the 'H NMR and 1C NMR spectra on the next page, determine a structure of this unknown molecule that is consistent with all data. Draw the structure of this molecule below (circle your final answer). H₃C NOL CH3 ON NO 2 Arso SATISFACTORY ONNO NOZ e. (5 points) Provide an explanation for the fact that the singlet at 9.4 ppm in the 'H NMR spectrum appears so far downfield. 2 NO₂ (e-WITHDRAWING) DESHIELD PROTONS ON AROMATIC IRING SIGNIFICANTLY. 1. (EXTRA CREDIT, 5 points): What is this compound, and what is its most notorious physical property? (2,4,6)-TRINITRO TOLWENE (TNT). 2 EXPLOSIVE. 2. (20 points) Using only ¹H NMR spectroscopy, how would you conclusively distinguish between all 3 isomers (ortho, meta, and para) of bromophenol? Be as specific as necessary in order to differentiate ortho from meta, meta from para, and ortho from para. (Suggestion: Use chemical structures as part of your answer.) OH Br OH Br OH Br SPIN-SPIN COUPLING CAN DIFFERENTIATE ALL 3 FROM ONE ANOTHER Para: H OH Br H H each H (or dd) J=7-8, 2 (meta coupling) J=7-8 DEPENDING ON STRENGTH OF MAGNET USED, THIS COUPLING MAY OR MAY NOT BE EVIDENT IN H NMR SPECTRUM. ortho: Ha OH Hb Hd Br or Ha OH Hb Hd Br JHa-Hb: 7-8 Hz JHa-Hc: 7-8 Hz Jhb-Hc: 7-8 Hz Hc: SAME PATTERN AS Hb: dd Hd: dd IF META COUPLINGS DETECTABLE, THEN EACH PROTON HAS 1 ADDITIONAL 2 HZ-COUPLING: JHa-He, Jhb-He, etc. meta: OH Br H H H WILL BE SINGLET (ONLY ONE) J=2, 2 IF MAGNET OF HIGH ENOUGH FIELD) 3. (20 points) An unknown compound X (containing only carbon, hydrogen, and oxygen) has m/z = 172 (M) and 115, and its ¹³C NMR spectrum is below. When treated with lithium aluminum hydride in ether, a single compound Y is produced, and its ¹H NMR spectrum is given below. In the space below the NMR spectra at the bottom of the page, draw the structures of X and Y. Circle your final answers and clearly indicate which is compound X (12 points) and which is compound Y (8 points). ¹³C NMR of compound X RO-R' (ester or carboxylic acid-H) Probably R-O-R', so probably ester ¹H NMR of compound Y 9H (t) 2H 1H (broad) Double-check: MW = 172, C₁₀H₂₀O₂ So: R-O-R' + LiAlH₄ → RCH₂OH + R'OH BUT RCH₂ = R', because both alcohols are "Y" ∴ Y = RCH₂OH = CH₃OH X = CH₃COOCH₃ 4. (24 points) Mass spectrometry was performed on 5-phenyl-2-pentanone (below), and several signals corresponding to fragments (M,) were observed in the spectrum. Write the m/z value observed for M' in the box provided (3 points). In each question below the m/z value for M, is provided. Draw the structure of My in the corresponding box (3 points each). Also, write the molecular weight of the neutral species (Mura) formed in each fragmentation in the boxes on the right (1 point each). Finally, draw the structure of each (Mute) in the boxes on the right (3 points each). BE SURE TO INDICATE WHETHER EACH M and EACH Mreusar is a radical (i.e. has an unpaired electron). a ct HC M = 162 CH40 mw = 162 M+ = 162 (Write the structure of Mrt here.) (Write the structure of Mneutral here.) a. ACYLIUM •CH3 OSC Ph ION) m/zfor M/ 147 mass of Mneutral = 15 (Write the structure of Mt here.) b. (tropylium ion) m/z for M = 91 (Write the structure of Mneutral here.) HCH₂ mass of Mneutral= 71 (Write the structure of My here.) C. MCLAFFEIZTY REARRANGEMAT +(radical cation) m/z for M, 58 (Write the structure of Mneutral here.) mass of Mneutral= 104