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Problem Set 6: Stereochemistry-1 Chemistry 260 Organic Chemistry 1-5. Assign absolute stereochemistry (R, S) to the stereogenic centres in each of the following molecules. Use the following answer choices: (1) R (2) S 1. 2. H H 3C Cl H3C Br C 3. Br CH3CH2 C C CH2CH3 CH2CH3 4. CH3 I Br 5. CH3 C HOOCCH2 COOH C H NH2 H NH2 6. Which of the following structures correspond to (R)-lactic acid from milk? (1) (2) HOOC H3C (3) CH3 HOOC OH C H C CH3 H (4) CH3 C H H3C COOH OH C COOH 1 C H (5) H HO COOH OH OH 7. The natural amino acid, cysteine, HSCH2C(NH2)H-COOH is in the R configuration. Which of the following structures correspond to (R)-cysteine? (1) (2) H H2N (3) H2N H CH2SH C COOH (4) C H H2N COOH C CH2SH COOH (5) H 2N H COOH COOH C H2N CH2SH 8. CH2SH C H CH2SH Given the following five structures, indicate for each pair listed below whether the structures are identical or isomers. (a) A and B (b) A and E (c) B and E (d) C and D (you might not get this yet, but give it a try) 9. By correctly assigning priorites, identify whether the following stereocenters are R or S. 2 10. A carboxylic acid with the molecular formula C3H5O2Br is optically active. Draw the structure of the R-isomer. 11. Provide a structure for the following compounds. (a) (R)-3-methylpentanoic acid (b) (S)-5-ethyl-2-methyloctane 12. Assign the absolute stereochemistry (R,S) to the stereogenic (asymmetric) center(s) in each of the following molecules 3 . 13. Draw all of the constitutional isomers and stereoisomers of compounds named tribromocyclobutane (all structures must contain a cyclobutane ring). Do not draw any isomer twice. 4