Organic Chemistry 315 Exam I Fall 2024 PDF

FALL 2024 – Organic Chemistry 315 Exam I Oct 7, 2024 Instructions: 1. Fill out all the required fields below NEATLY and LEGIBLY within the boxes. 2. PRINT your first and last name on the top o...

FALL 2024 – Organic Chemistry 315 Exam I Oct 7, 2024 Instructions: 1. Fill out all the required fields below NEATLY and LEGIBLY within the boxes. 2. PRINT your first and last name on the top of all pages. 3. Read the pledge and sign your name BEFORE handing in your exam. PRINT your first and last names: First name Last name Enter your NetID Enter your RUID, one digit per box: Enter your Section number, one digit per box: “On my honor, I have neither received nor given any unauthorized assistance on this examination.” Signature: Do NOT remove this page from your exam. First Name _____________________ Last Name ______________________ Section_______ Multiple Choice: Please clearly circle the one correct answer for each question. 1. What is the correct formula of the molecule below? OH H 2N OH Br Cl A. C15H23BrClNO2 B. C15H25BrClNO2 C. C16H23ClBrNO2 D. C16H23BrClNO E. C15H22ClBrN2O 2. What is the double bond equivalent (DBE) of the molecule below: Cl NH2 A. 5 B. 6 C. 7 D. 8 E. 9 3. Which one of the following molecules is not aromatic? (hint: consider the factors that can affect the relative importance of resonance structures) O N S N A B C D E F24 315 EXAM I A1 2 First Name _____________________ Last Name ______________________ Section_______ 4. Which one of the following statements is true? A. The chemical shift of the protons in 1H NMR is dependent on the field strength of the main magnet of the instrument. B. Carbon NMR captures the signal from 12C nuclei. C. High-resolution mass-spectrometry can differentiate ortho-, meta- and para-dichlorobenzene (structures are shown below). D. Mass-spectrometry is a technique that measures the mass-to-charge ratio of either positive ions or negative ions. E. The IR signal of O-H bond stretching shows at high wavenumbers because lighter atoms vibrate slower than heavier atoms. Cl m-dichlorobenzene Cl Cl Cl Cl Cl o-dichlorobenzene p-dichlorobenzene p-dichlorobenzene o-dichlorobenzene 5. Which one of the following structures has the correct formal charge assigned? O HN H N HO O H Cl A B C D E F24 315 EXAM I A1 3 First Name _____________________ Last Name ______________________ Section_______ 6. Acetylsalicylic acid is a widely used OTC drug with brand names such as Aspirin. Which one of the following is the correct 13C NMR spectrum of the molecule? O O A. O OH acetylsalicylic acid 180 160 140 120 100 80 60 40 20 0 PPM B. 220 200 180 160 140 120 100 80 60 40 20 0 PPM C. 200 180 160 140 120 100 80 60 40 20 0 PPM D. 140 120 100 80 60 40 20 0 PPM E. 180 160 140 120 100 80 60 40 20 0 PPM F24 315 EXAM I A1 4 First Name _____________________ Last Name ______________________ Section_______ 7. Rank the following (I-IV) in the order of decreasing pKaH O NH2 H H2C CH N I II III IV A. pKaH I > III > IV > II B. pKaH II > I > IV> III C. pKaH II > I > III > IV D. pKaH I > II > IV > III E. pKaH IV > III > II > I 8. When an aldehyde reacts with an alcohol to form hemiacetal, which molecular orbital of the aldehyde is filled by the electron pair from the alcohol? A. σ B. σ* C. π D. π* E. HOMO 9. Which description of structures I and II is correct? I II A. I and II are two isomers. B. I and II can interconvert with each other very fast. C. I and II have the same geometry. D They both have 2 sp2 hybridized carbon atoms. E. I and II are resonance structures with different electron cloud distribution. F24 315 EXAM I A1 5 First Name _____________________ Last Name ______________________ Section_______ 10. Which one of the following compounds has the lowest activation energy in the rate determining step of its cyclization? O A. H OH O B. H OH Cl O F C. OH O F D. H OH O E. OH Cl F24 315 EXAM I A1 6 First Name _____________________ Last Name ______________________ Section_______ For open-ended questions, only answers in the designated space (lines, parentheses, boxes) are graded. Feel free to use extra space as scratch paper but the content will not be considered for grading. 11. Listed a-g are the π molecular orbitals of 1,3,5,7-octatetraene. Please fill in the blanks. (1 pt each, 4 pts total) a d g b e h c f Orbital ____ has the highest energy. Orbital ____ has the second lowest energy. Orbital “h” has ____ node(s). Orbital ___ is the LUMO. 12. For each group below, circle the one with lower pKa (i.e., more acidic). (2 pts each, 16 pts total) 1) 2) OH NH2 3) 4) O Cl OH OH 5) 6) OH OH H N H 7) N 8) H 2O OH F24 315 EXAM I A1 7 First Name _____________________ Last Name ______________________ Section_______ 13. Draw a resonance structure of the following molecules, with proper curved arrows. For b), you only need to draw one of the more important resonance structures. (4 pts total) O a) N H O b) 14. Write the major organic product containing the aromatic ring in the following reactions. (2 pts each, 6 pts total, no partial credits) O excess NaBH4 O O aqueous EtOH 1. BuLi, THF Br 2. CO2 + 3. H3O OH PCC, CH2Cl2 OH 15. Write the number of signals in the 13C NMR spectrum below each molecule. (2 pts each, 6 pts total) O O N O O Number of 13C NMR signals F24 315 EXAM I A1 8 First Name _____________________ Last Name ______________________ Section_______ 16. Use curved arrows to show the mechanism of the following transformation: (4 pts total, may have partial credits) OH O H 3O + O HO F24 315 EXAM I A1 9 First Name _____________________ Last Name ______________________ Section_______ 17. The pKa of methane is approximately 56 in DMSO, which is what is expected for a proton from C-H on a “normal” sp3 hybridized carbon atom. However, the following compounds show much lower pKa. O O O 9,10-dihydroanthracene fluorene acetone Acetylacetone = 30.1 pK = 22.6 = 24.4 pK = 14.2 pKa a pKa a 1) Why the pKa of these compounds are much lower than a typical alkane (pKa>50)? Use proper resonance structure to explain the stabilization of each conjugate base (Short text can be used to aid the justification, but may not be necessary (4 pts). arrows can help write the resonance structures, but are not required). 2) Why fluorene has a significantly lower pKa than 9,10-dihydroanthracene? (2 pts) Overly long explanations containing excessive irrelevant information will not get any credits, even if they contain the right answer within. F24 315 EXAM I A1 10 First Name _____________________ Last Name ______________________ Section_______ 18. Propose the molecular structure based on the information provided, and draw the structure in the rectangular box below (4 pts). 1) high-resolution mass-spec suggests a formula of C10H10O2. The DBE is. (1 pt) 2) The IR spectrum is shown below: Circle the functional group suggested by IR: Hydroxyl group; carbonyl group; C≡C triple bond; amino group (1 pt) 3) The 13C NMR spectrum is shown below: 220 200 180 160 140 120 100 80 60 40 20 0 PPM (2 pts, no partial credit) F24 315 EXAM I A1 11 First Name _____________________ Last Name ______________________ Section_______ Scratch Paper F24 315 EXAM I A1 12