CHEM 243 ORGANIC CHEMISTRY I Fall 2018 Exam II Information and Study Guide

Transcription

1 CHEM 243 ORGANIC CHEMISTRY I Fall 2018 Exam II Information and Study Guide page 1 CHEM 243 Exam II is scheduled for Monday, November 5 in DMF 477 & 481 (lab rooms). You must take the exam during your normal class time, so do not be late! I will allow 15 minutes of extra time if needed (start a little early or stay a little late). If you need accommodations for this exam you must provide me with the pink sheet from the Academic Achievement Center no later than MONDAY, OCTOBER 29. PLEASE NOTE: I require two weeks notice if you will not be on campus the day of the exam due to a BSU sponsored event! Preparing for the Exam! You are responsible for developing a Study Schedule that will give you 5-7 days to thoroughly review material for this exam. Make a list of questions that can be answered during class meetings or office hours. The following course resources are available to help you study for this exam: (1) Lecture videos (2) Your class notes (3) Class worksheets (4) This Exam Study Guide (5) Review worksheet in Wednesday s class (6) Peer Leader Review Session on Thursday REMINDER: There are two binders of CHEM 243 information in the 4 th floor lounge, and I also have loaner textbooks available! Peer leaders, Prof & Pizza Review Session: Thursday, November 1, 3-6 PM, DMF 4 th Floor Lounge (pizza arrives ~5:30 PM) Miscellaneous Notes: 1. There will be an attendance sheet for you to sign before I give you your exam. 2. Exams may be answered in blue or black ink or black lead pencil. 3. Be neat! If I can t read your writing I can t grade your answer. I provide you with scrap paper to work out your answers. Use it! 4. You will not be allowed to share any materials with another student during the exam. 5. You will be provided scrap paper, a periodic table, appropriate data tables, and molecular models. I DO NOT provide pens or pencils. 6. Cell phones and other electronic devices must be muted and put away during exams. There is a 10-point penalty for any disruption caused by these devices. If you need your cell phone, please let me know. 7. Academic dishonesty on exams will result in dismissal from the class and an F course grade. Policy on Missed Exams. Missing an exam will result in a zero exam grade. Typically, I DO NOT give makeup exams with the exception of unusual personal or family emergencies, or illness that requires the care of a physician. It is up to you to provide acceptable verification for your excuse. If you miss the exam, you must contact me by phone or by 12:00 Noon on the day of the exam. It is up to my discretion to give you a make-up exam, at my convenience, on the day following the scheduled exam date. Please note that every effort will be made to keep the make-up exam at the same level of difficulty as the regularly scheduled exam. Students are allowed one make-up exam per semester, including the final exam. I do not give incompletes. If you simply arrive late and have a reasonable excuse, you can still take the exam!

2 page 2 KEY CONCEPTS FOR REVIEW. Start by reviewing Exam I; all Exam I material is fair game. Exam II will cover all lecture material through video 6-9. Chapter 5: Chirality and chiral centers; stereoisomers; (R,S) configurations at chiral centers and nomenclature; drawing 3D zig-zag structures; comparing structures (constitutional isomers, identical, different, conformers, geometric isomers, enantiomers, diastereomers, meso compounds); Fisher Projections; racemic mixtures. Chapter 6: Substitution and elimination reactions of alkyl halides; characteristics and mechanism of the SN2, E2, SN1, E1 reactions; using energy diagrams and transition states to explain mechanisms; predicting the products of SN1, SN2, E1, E2 reactions; writing SN2, E2, SN1, E1 mechanisms using the curved arrow format SUPPLEMENTAL REVIEW PROBLEMS. These are additional problems to help you review for the exam; I will post an answer key by Monday. These problems should be included with your review of the lecture videos, class notes, worksheets, and the posted resources. 1. Answer the following questions as indicated. (a) Chiral Carbon. How many chiral centers Can you find in the molecule drawn to the right? Place a dot ( ) on each chiral center. This compound has a maximum of stereoisomers. (b) If a molecule has three chiral centers with configurations (1R, 2R, 5S), what would be the configuration of: (i) an enantiomer: (ii) three diastereomers: (c) Circle the most accurate structure(s) for (R)-3-bromo-2,3-dimethyl pentane. (d) Which of the following molecules will have at least one diastereomer? Circle your choice(s). (e) TRUE or FALSE A racemic mixture occurs when a mixture of constitutional isomers are present. If the statement is FALSE, correct the statement.

3 page 3 (f) Are the following terms best associated with SN1, SN2, E1, or E2 reactions? Some terms may have more than one answer. bimolecular transition state stereospecific concerted mechanism carbocation intermediate steric hindrance in the transition state racemic mixture substrate reactivity: methyl << 1 o < 2 o < 3 o substrate reactivity: methyl > 1 o > 2 o >> 3 o crowded transition state solvolysis strong base poor nucleophiles nucleophilicity alkenes formed as products (g) Rank the reactivity of the following alkyl halides in an SN1 reaction (1 = most reactive...4 = least reactive). (h) Rank the following nucleophiles relative to their SN2 reactivity toward 2-bromopropane (1=fast..4=slow). Cl - HO - NH2 - F - (i) Which nucleophile in each pair will react faster in SN2 reactions? Circle one choice in each pair. PH3 or - PH2 CH3O - or (CH3)3CO - H2S or H2Se - NH2 or - F (j) The transition state structure shown below is most consistent with which type of mechanism? Circle your choice. E2 E1 SN1 SN2 (k) Rank the reactivity of the following alkyl halides in an SN2 reaction (1 = most reactive...5 = least reactive).

4 page 4 (l) Rank the following alkenes in order of increasing stability (1 = least stable...4 = most stable): (m) Rank the following substances in order of their ability to produce increasing amounts of E2 elimination product with 2-bromobutane. (1 = least E2 product..3 = most E2 product). NaOH NaNH2 KF 2. Nomenclature. If a name is given draw an accurate structure. If a structure is drawn, give an accurate IUPAC name. You must show the 3-D configuration for all chiral centers. (a) (S)-1,4-dichloro-2,2-dimethyl pentane (c) Draw the correct line structure and Fisher projection for (meso)-4,5-dichloro-4,5-diisopropyl octane (d) Draw a 3D structure and give an IUPAC name for the organic compound represented by the Newman Projection drawn below. You must show the correct 3D configuration for all chiral centers.

5 3. Comparing Organic Structures. How are the following pairs of molecules related? page 5 Identical Constitutional Isomers Enantiomers Diastereomers

6 page 6 5. Reactions. Complete the reactions shown below by drawing the structure of the major, neutral organic products. Draw the proper stereochemistry, if relevant. DO NOT write the mechanism for the reactions. Remember, there may be combinations of SN1/E1 and SN2/E2! Use your flow chart: Is the alkyl halide 1 o, 2 o or 3 o? Is the Nuc poor or good; weak or strong base; small or bulky? Is the mechanism(s): SN1, SN2, E1, E2?

7 6. Mechanisms. page 7 (a) Reaction Theory I. Consider the balanced, net equation for the SN2 reaction shown below. (i) How can you tell that an SN2 substitution reaction actually occurred? Explain your answer. (ii) Based on your answer above, write a complete mechanism (one step) that explains the formation of all products in the balanced net reaction. Your mechanism must consist of a balanced chemical equation, and curved arrows to show electron pair movement. (iii) Draw a completely labeled Energy Diagram for this exothermic reaction, label the axes, and designate the reactant, product, transition state, and activation energy. Also draw the structure for the transition state in this reaction. (iv) Which of the following best describes the role played by the reactant Br - in this reaction? Circle all that apply. Acid Base Nucleophile Leaving group None of these

8 page 8 (v) Explain how both the product and the transition state provide information that this reaction is stereospecific. (vi) Based on your transition state structure, explain whether the rate of reaction would change if the alkyl halide reactant was changed from: (b) Reactions Theory II. Consider the balanced, net equation shown below. (i) Which of the following mechanism steps are part of the overall reaction shown above? Circle all that apply. SN1 acid/base SN2 E1 E2 (ii) Based on your answer above, write a complete mechanism that explains the formation of all products in the balanced net reaction. Your mechanism must consist of a series of individual, balanced chemical equations, and curved arrows to show electron pair movement. HINT: There are 3 steps.

9 page 9 (iii) Draw a completely labeled Energy Diagram for this exothermic reaction, label the axes, and designate the reactant, product, transition state(s), intermediate(s), and activation energy for the Rate Limiting Step (RLS). Also draw the structure for the transition state of the slow or rate-determining step in this reaction. (iv) Which of the following best describes the role played by H2O in this reaction? Circle all that apply. nucleophile spectator acid base leaving group (v) Is this reaction stereospecific? Explain why or why not. (vi) Would the rate of the reaction change if the Br Lg was replaced by I as Lg? Briefly explain. (vii) Would the mechanism change if the nucleophilic reagent was NaCN? Briefly explain. (c) SN2 Mechanism (2 steps). Write a complete mechanism that explains the formation of all products in the balanced net reaction shown below. Your mechanism must consist of a series of individual, balanced chemical equations, and curved arrows to show electron pair movement. I NH + 2 NH3 2 + NH 4 + I

10 page 10 (d) SN1 Mechanism (3 steps). Write a complete mechanism that explains the formation of all products in the balanced net reaction shown below. Your mechanism must consist of a series of individual, balanced chemical equations, and curved arrows to show electron pair movement. (3) E1 Mechanism (2 steps). Write a complete mechanism that explains the formation of all products in the balanced net reaction shown below. Your mechanism must consist of a series of individual, balanced chemical equations, and curved arrows to show electron pair movement.