CHM 251 Organic Chemistry 1

Transcription

1 CM 251 rganic Chemistry 1 NAME Fall 2008 omework #2 Due: Tuesday, ctober 7, 2008 at 7 am Print out this assignment and complete all of your work on these pages. Question #1 Rank the following alkenes in order of MST to LEAST exothermic upon catalytic hydrogenation of each to its corresponding alkane (this reaction is described in Section 10.2). Alkene 2 Pd-C Alkane + EAT Provide a brief explanation that describes why the reactions are ordered as observed. What is the major stabilizing effect that determines the stability order in this series? INT: you ll likely want to draw the structure of each before you proceed. (a) cis-2-hexene (b) 1-hexene (c) 2,3-dimethyl-2-butene (d) 2-methyl-2-pentene (e) trans-2-hexene energy relative enegy of product (a) (b) (c) (d) (e)

2 Question #2 The following sets of question pertain to intermolecular forces: (a) Provide a valid structure for each of the following molecules and then, arrange the compounds in order of increasing boiling point (you may want to consult the Aldrich catalog, an MSDS, or go to chemfinder.com to find the bps). iefly explain your ordering being sure to indicate the type and relative magnitude of intermolecular interactions (e.g. VDW interactions, dipole-dipole, and hydrogen bonding) that exist in each case. 1. dichloroethanoic acid (dichloroacetic acid) 2. 2-methoxybutane 3. ethyl 3-oxobutanoate (ethylacetoacetate) 4. n-heptane 5. 3,3-dimethyl-2-pentanol 6. 3-amino-1,2-propanediol 7. ethane (ethylene) (b) Predict which of the following salts is likely to have unusually high solubility in a (nonaqueous) hydrocarbon solvent. iefly explain your choice. C 4 9 N 4 Cl vs. C 4 9 N (C 2 ) 15 C 3 C 4 9 (c) Normally, the drug shown below is much more soluble in lipid-like solvents (e.g. benzene) than it is in water. owever, its water solubility INCREASES considerably when the aqueous solution contains moderate amounts of strong acid (e.g. in the stomach) as shown by the reaction below. Explain the solubility differences. + soluble in benzene + 2

3 Question #3 The following compound was recently reported in the Journal of Medicinal Chemistry as a key synthetic intermediate in the synthesis of a potent plant-derived natural product used in the treatment of cancer. Ph C 3 C 3 Conformational Interaction Δ (kcal/mol) 1,3-diaxial ( and ) 1.3 1,3-diaxial (C 3 and ) 1.7 1,3-diaxial (C 3 and t-butyl) 3.8 1,3-diaxial (C 3 and C 3 ) 2.3 1,3-diaxial (C 3 and ) 2.4 1,3-diaxial (Ph and ) 1.9 1,3-diaxial (Ph and t-butyl) 4.1 1,3-diaxial (Ph and C 3 ) 3.2 1,3-diaxial (Ph and ) 3.5 1,3-diaxial ( and C(C 3 ) 3 ) 2.7 1,3-diaxial ( and C 3 ) 0.9 Gauche (t-butyl and ) 2.7 Gauche (t-butyl and C 3 ) 2.3 Gauche ( and C 3 ) 1.8 (a) Name the structure shown above WIT assignment of R/S configuration for each stereogenic atom. (b) Draw the two chair conformations (using the templates provided) of the structure above. Be sure to LIST all destabilizing interactions and provide a value for total potential energy (E) for each conformation (more stable and less stable). more stable less stable E = E =

4 (c) Find the potential energy difference (Δ) between the two possible conformations and use this value to determine the equilibrium constant (Keq) for the chair flip from the MRE stable to the LESS stable conformation. Do your values for Δ and Keq make sense? Question #4 For the following pairs of molecules, assign the absolute configuration (R or S) to each stereogenic carbon and indicate the stereochemical relationship (identical, enantiomers, diastereomers, constitutional isomers, or meso compound) between the two molecules in each pair. Pair #1 C 3 Pair #2 Cl 3 C 3 C Cl Pair #3 C 3 C 3 Pair #4 3 C 3 C 3 C Pair #5 C 3 C 3

5 Question #5 Mirror Images Pharmaceutical Corporation has designed a novel neuromuscular blocking agent and wants to submit the molecule shown below for patent approval. You are the lead organic chemist on the legal team and have been asked to investigate certain aspects of stereochemistry in order to submit a report along with the patent application. Your report requires the following information: C 3 C 3 C 3 C 3 (a) Identify all stereocenters that are not asymmetric carbons in the molecule on the RIGT--- label with an SC (b) Identify all asymmetric carbons in the molecule on the LEFT--- label with an AC (c) Assign the configuration about all stereocenters and asymmetric carbons on BT molecules --- use E/Z or R/S assignments (d) Provide the complete IUPAC name for the compound on the LEFT --- identify the longest chain and any priority groups (e) Show all polar covalent bonds by writing in the dipole arrow for the molecule on the RIGT (f) Identify the stereochemical relationship between the two molecules (identical, enantiomers, diastereomers, constitutional isomers, or meso)