CEM 251 Exam 3A Spring 2018

Transcription

1 A Α NAME Section CEM 251 Exam 3A Spring 2018 READ TIS! Bubble in your PID in the space above. Write your answer for each question in the space provided. Score The absence of any of the above identifiers will result in the deduction of 2 pts from your score LEAVE TIS CVER SEET ATTACED T TE QUIZ! 1. /13 2. /21 CIRCLE TE BELW If you are in the onors College and Registered for the CEM251 onors ption 3. /20 4. /28 5. /18 TTAL: / 100 NRS PTIN /10

2 1) Identify the indicated sets of protons as (U)nrelated, ()omotopic, (E)nantiotopic or (D)iastereotopic (4 pts) 2) ow many kinds of nonequivalent protons () are present in the following? That is how many different proton signals will you observe in a 1 -NMR. int: remember topicity and to draw out each new molecule with a "replacement atom" for 's on wedge and dash bonds (2 pts) of 3) Arrange each set from 1 (slowest) to 3 (fastest) reactant in an S N2 reaction. (3 pts) N C 3 Ts Ts = S 4) Indicate whether the following molecules are (C)hiral and (A)chiral with the appropriate letter. int: redraw these out as line bond structures with wedge and dash bonds in the space at right. (4 pts) C 3 C 3 1A

3 5) Draw the Fischer projection onto the zigzag line bond structure scaffold at the right using wedge and dash bonds. The dot is a reference guide. (5 pts) 6) CLEARLY Draw the compound below with wedged ( ) and/or dashed ( ) lines to show the 3-D aspect of the chirality centers. (6 pts) S N 2 C 3 R R 7) Draw. (5 pts) Answer in box. Use workspace below box to workout stereochemistry. (E)-3-(1,1-dimethylethyl)-2,4-dimethyl-3-hexene 8) Name. Use stereochemical descriptors with their numerical location(s) in the name. (5 pts) 2A

4 9) Identify whether the following molecules are (E)nantiomers, (I)dentical, (D)iastereoisomers, (C)onstitutional Isomers, or (N)ot isomers. Place appropriate letter in the box. (4 pts) 10) (8 pts total) Using the conditions shown, draw ALL the product(s) for the MST LIKELY reaction mechanism below (Include stereochemistry, if necessary). (7 pts) Circle the reaction mechanism below the arrow (E2, S N2, E1 or S N1 below). (1 pt) Take your time. 3 C C 3 DMS Na E2 E1 S N 2 S N 1 If fewer than 3 products place an X in the box(es) not used Draw DMS (1 pt Bonus) 11) (8 pts total) Using the conditions shown, draw ALL the product(s) for the MST LIKELY reaction mechanism below (Include stereochemistry, if necessary). (7 pts) Circle the reaction mechanism below the arrow (Circle E2, S N2, E1 or S N1 below). (1 pt) Note the reactant above arrow; remember what it can NLY function as. Take your time. Ts C 3 C 2 S E2 S N 2 E1 S N 1 If fewer than 3 products place an X in the box(es) not used 3A

5 12) (10 pts total) Assign E or Z configuration (1 pt each). CIRCLE the highest priority groups used to assign the configuration. (2 pt for each circle) 3 C C C REM: CIRCLE the highest priority groups 13) Arrange the following in order of increasing stability (1 is LEAST stable; 4 is MST stable). (4 pts) 14) Draw a dot ( ) (this size) on the chirality center(s) in the compound. Write the total number of center(s) found in the box. If there are no chirality centers in the molecule, then write 0 in the box. (6 pts) here 15) Identify the products of the following Elimination reactions. (4 pts) 1) If only a one product is made, draw an X in the MINR box. 2) If no reaction draw X in both boxes 3) Disregard trans/cis stereochemistry as MAJR/MINR products for this problem. DBU MAJR MINR 16) If the following compounds are (M)eso write the letter 'M' in the box; otherwise write an 'X' in the box. (4 pts) 3 C C 3 4A

6 17) Fill in the missing products. (6 pts) Note: pyridine is a base used with Ts and is NT used to make a Substitution or an Elimination product in the first box. Ts Na Et pyridine acetone pyridine = N Major E product 18) Rotate the molecule so that the and as anti in the plane-of-the-paper (like this elimination reaction below (8 pts) ) for the C 3 = n the wedges and dashes of template below, draw the remaining substituents to show the conformation need for an E2 reaction. REMEMBER: are hidden in LINE BND structure. YU WILL NEED T SW TEM IN YUR DRAWING 19) Now, draw the E2 product from the starting material (above) (like this as shown in class) with substituents in appropriate positions. (4 pts) C 3 DMS D NT REMVE TE LAST PAGE 5A

7 onors Question (FR NRS STUDENTS NLY; NT EXTRA CREDIT FR NN-NRS STUDENTS) The following 1,2,3,4,5-pentamethylcyclohexanes contain chiral centers. Label the R/S stereoisomerism boxes next to arrows and number () the carbons 1 through 5 correctly. (1 pt per correct and R/S pair). onors 1: 3 C C 3 C 3 C 3 C 3 onors 2: Identify the pseudo chiral center in this molecule with a lowercase "r or s" AND CIRCLE IT!. 3 C C 3 C 3 C 3 C 3 6A