Stereochemistry Terminology for two pure isomeric compounds, both of which are chiral? A pair of stereoisomers

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1 Name Last, irst STEECEMISTY This handout will help you understand stereoisomerism, naming conventions and relationships between stereoisomers. I hope that you will use this to help you study for exam 1. Please answer all parts of all questions

2 Stereochemistry Terminology 1. Mark each of the following statements as true or false.for two pure isomeric compounds, both of which are chiral? B C D E G they must be enantiomers they must be configurational isomers they must be meso isomers they must be diastereomers none of these statements are true they must be constitutional isomers they must be tautomers they must both be optically active 2. pair of stereoisomers might be classified in various ways, depending on their exact nature. Which of the following terms could properly be applied to a pair of stereoisomers, assuming their nature permits. Be careful, some of these terms should never be applied to pairs of stereoisomers. B C D E they might be configurational isomers they might be diastereomers they might be constitutional isomers they might be tautomers they might be conformational isomers they might be enantiomers G they might be meso isomers none of these statements are true 3. Mark each of the following statements as true or false.. Enantiomers have the same boiling point. B. Enantiomers have the same chemical reactivity with chiral chemical reagents. C. Enantiomers have the same optical properties. D. Enantiomers have the same melting point. E. The reason for different biological activity of enantiomers is that only one of them binds to all receptor sites.. Enantiomers have the same chemical reactivity with achiral chemical reagents. G. Enantiomers have the same density. 2

3 4. Mark each of the following statements as true or false.. Compounds composed of two chiral fragments are chiral. B. Compounds which can be reflected through a mirror plane are chiral. C. Compounds with plane of symmetry are achiral. D. Compounds with multiple chiral centers are chiral. E. The dl-prefix specifies configuration.. The DL prefix specifies the direction of rotation of light. G. The d-prefix means the compound has the same configuration as d- glyceraldehyde.. The d-prefix means the compound rotates plane of polarized light to the right. I. Constitution is a composite term including structure, configuration and conformation. J. Tertiary amines with three different substituents are chiral. K. The precedence rules can be used to determine E/Z -configuration of ring compounds. L. The cis/trans-prefix specifies configuration. M. Diastereomers can be distinguished by their melting point or other physical properties. N. Mirror images of a compound are enantiomers. Meso-compounds are achiral. P. The specific rotation of a compound is dependent upon the concentration of the substance. Q. otation by 90 o of any compound is equivalent to mirror reflection.. In-plane rotation of the isher projection by 90 o is equivalent to mirror plane reflection. 5. ll of the naturally occuring amino acids are called L because they have a stereochemistry like L- glyceraldehyde, shown below. ll of the amino acids have the S absolute configuration except glycine and cysteine, explain why they are different. 2 N C C 2 N C C 2 N C C 2 N C C C 2 C 2 S L- glyceraldehyde L- amino acids glycine cysteine 3

4 ssigning & S Configurational Prefixes 6. Using the letter assigned to each group, put the following functional groups in decreasing order of Cahn-Ingold-Prelog priority. C C 2 B C D E N 2 N 2 G I NSWE: 7.ssign the absolute configuration at each stereocenter in the following molecules. N 2 2 N 3 C 2 N N N 2 3 C 3C 3 C 3 C 4

5 8. Use the diagrams below (-EE) to complete the following. C 2 5 C 2 C 2 5 CC 2 5 C 2 5 C C 2 5 C( ) 2 B C D E G I J K L M N P Q S T U V W X Y Z BB CC DD EE a. Label each stereocenter above as or S. b. List the letter associated with the structures that are chiral. c. List the letter associated with the structures that are achiral. d. List the letter associated with the structures that are meso. 5

6 211 LSW 10 Name 9. a. Label each stereocenter below as or S. b. edraw each of the following compounds as a isher projection. c. Circle any molecule that is meso.. C 2 B. 10. or each structure below 1. label each chiral carbon as () or (S) 2. draw in any internal mirror planes of symmetry 3. Circle any meso structures 3 C C 3 C3 C 3 B C C 3 3 C 3 C D E 6

7 11. ssign the absolute configuration (,S,E and Z) in the compounds shown below. C 2 C C 3 3 C 3 C N 3 C 3 C 3 C 3 C 3 C C 3 C 3 3 C C 3 Ph Ph 7

8 12. Indicate the structures that satisfy the specified condition. If there is no structure that fits the description use X. (1) Which hydroxybutanal structures have a configuration? (2) Which hydroxybutanal structures have a S configuration? (3) Which dibromo structures have a 2-(), 3-(S) configuration? (4) Which dibromo structures have a 2-(), 3-() configuration? (5) Which dibromo structures have a 2-(S), 3-() configuration? (6) Which dibromo structures have a 2-(S), 3-(S) configuration? 13. Draw wedge hash models for all of the isomers that have a molecular formula C 3 7 I 8

9 14. Give complete names for the following compounds, include or S designation. C 3 3 C 9

10 211 LSW 10 Name 15. Determine whether the pairs of compounds shown below are positional, optical, geometric or conformational isomers. Identify all stereocenterss as or S and all geometric isomers as E or Z. 3 C 3 C C 3 C 3 C 3 3 C 3 C C C 2 N 2 N C C 3 C 3 C 3 C 3 C 10

11 16. Indicate whether the pairs of structures below are (a) identical compounds, (b) structural isomers, (c) enantiomers or (d) diastereomers. Label each pair with an a, b, c, or d. Ignore any differences in conformation. 3 C 3 C 3 C 2N C 2 ) B) C) 3 C C 3 3 C ) 3 C G) D) E) ) I) 3 C K) J) C C L) 2 C M) C 2 11

12 17. Use the molecules below to complete the following statements. a) Identify each stereocenter as the () or (S) configuration. b) Write the letters of the molecules that are meso isomers. c) Write the pairs of letters of the molecules that are enantiomers. D) Write the pairs of letters of the molecules that are diastereomers. ) B) C) D) I I I I E) ) G) ) I) J) K) L) M) N) ) P) 12

13 18. Indicate the relationship between pairs of the following compounds drawn below: ) Constitutional isomers B) Enantiomers C) Diastereomers D) Identical compounds Examples: nswer nswer D B C D E G I J K L M N 13

14 P Q S W Y V Z 19.ow many stereoisomers will exist for each of the following molecules? Draw the stereoisomers. Which would be expected to potentially exhibit optical activity? (a) 1,4-dimethylcyclohexane (b) 1,3-cyclopentanediol 14

15 211 LSW 10 Name 20. Given the isher projection X shown below 3 C ) 3 C X Determine the relationship each of the following structures to X. B) 3 C D) C 3 3 C ) G) 3 C 3 C 21. n optically pure compound gave [ ] D mixture of and its enantiomer B gave [ ] D What is the ratio of to B in the mixture? (Show work) 15

16 22. Tartaric acid is an important compound in the history of stereochemistry. Two naturally occurring forms are optically inactive. ne form has a melting point of 206 C while the other melts at 140 C. The inactive tartaric acid which melts at 206 C can be separated z into two optically active forms with [ ] D + 12 and [ ] D , respectively. Both optically active forms melt at 170 C. Tartaric acid which melts at 140 C cannot be separated into optically active forms. a) Draw wedge hash diagrams of each structure on the drawing below. b) Identify the relationship between the various isomers. c) Can you be sure which tartaric acid in part b is dextrorotatory and which is levorotatory? C C C C C C elation to i elation to ii elation to iii 140 C 170 C 170 C i. ii iii 23. Muscarine is the poisonous component in poison mushrooms. (-)-Menthol is a common ingredient in commercial compounds due to its fragrance. a) Indicate the number of possible stereoisomers for each structure. b) The configuration of biologically active muscarine is 2S,3,5S. Using wedge hash diagram on the structure below draw muscarine, showing the absolute stereochemistry. c) or (-)-menthol assign each stereocenter /S configuration. Name Muscarine (-)-Menthol Structure 3 C 3 C 3 C N + - Number of stereoisomers possible 3 C C3 16