1. Use appropriate curved arrows to indicate the complete mechanism of each of these reactions. KH (1 equiv.) + KCl THF. + HBr.

Transcription

1 1. Use appropriate curved arrows to indicate the complete mechanism of each of these reactions. K (1 equiv.) TF K enantiomer While writing the mechanism, justify both the regiochemistry the relative stereochemistry shown here. Make sure that you underst these terms. 2. A pure chiral compound has a specific rotation of 100. Determine the % composition of an enantiomeric mixture of this compound that has a specific rotation of Draw the appropriate structure in each empty box based on the compound(s) type of arrow provided. - S - S Na - : 3 ether NaTs

2 4. Draw the mirror image of this molecule in the box to the right. Is the above molecule chiral or is it a meso compound? 5. Assign the stereochemistry in each of the following molecules, using the ahn-ingold-prelog priority rules. In each blank, indicate either, 'R', 'S', 'E', 'Z', or 'N/A' (for 'not-applicable', when a particular atom is nonstereogeni i) ii) iii) i) ii) iii) e) N 2 N 2 6. In the blanks below the molecules label each molecule as 'chiral' or 'achiral' Which of the following pairs of carbon atoms in this molecule are not chemically equivalent to one another? A & D F & A & E e) none of the above (i.e., all are equivalent) B & F A G B E 3 D 8. Which of the following carbocations is not resonance stabilized? 2 3 e)

3 9. Which of the following pairs of molecules are not constitutional isomers of one another? 10. Which of the following pairs of molecules are cis/trans stereoisomers of one another (i.e., not a pair that are simply drawn differently nor constitutionally isomeri? none of the above f) all of the above e) 11. Draw the full mechanism for the formation of the product shown here. 3 (cat.) ow does the difference in stereochemistry between these two starting materials affect the type of products formed from this reaction. Draw the major elimination product expected in each case explain why it is the major one. ( ) 2 K DMS ( ) 2 K DMS

4 13. The following reaction occurs via an E2 mechanism, in which an alkene (II) is formed via a β- elimination reaction of the bromine in I. The stereochemistry of the product is not shown, but one alkene stereoisomer does predominate in this reaction. Ph KtBu DMF 2 Ph 2 I II Draw a Newman projection (or a comparable drawing which clearly indicates conformation) of the reactive conformation of I. Using the information from (, determine the stereoisomer of the alkene (II) that results from this reaction draw it in the box below. 14. Provide the IUPA name for each of the following molecules, designating stereochemistry where appropriate using the R/S E/Z conventions. F Draw the following molecules: (Z)-6-ethyl-2-decen-4-yne (2R,4R)-4-methyl-2-octanol trans-2-methoxycyclohexanol (Note that this molecule is chiral, but only the relative stereochemistry is specified; thus, you may draw either enantiomer). 16. Draw each of the following stereoisomers in its most stable chair conformation. Then indicate whether the cis or trans isomer is lower in energy? Explain why. cis-1,3-diethylcyclohexane trans-1,3-diethylcyclohexane 17. Shown below are three contributing resonance structures for the conjugate acid of N-methylguanidine. N 2 N 2 3 N 3 N 3 N N 2 N 2 (A) (B) () i) Draw curved arrows, above, to indicate how you would "push" electrons in structures (A) (B) thus convert each to the structure on its right. ii) alculate the formal charges on all of the nitrogen atoms within each of the resonance structures (A, B, ). Write your answers beside the appropriate atoms, above. N 2 N 2

5 18. ircle the molecule with the lowest pk a (i.e., strongest aci in each of the following horizontal rows N N2 I F S N Show how you would synthesize each product from the starting material provided. Each synthesis takes at least two steps. Draw all isolable intermediates. ( ( 20. early explain why it would be impossible to prepare this compound via a Williamson ether synthesis. Then suggest a way that you could synthesize it (from phenol what else?) 21. When this reaction is performed in aqueous solution at 25, Δ = TΔS = propanoic acid acetate anion propanoate anion acetic acid Baed on the above information, what can you infer to be true? This reaction favors the formation of the products (propanoate anion acetic aci at 25. This reaction is endothermic. Raising the termperature of this reaction will favor the formation of more propanoate anion acetic acid. The starting materials disrupt the order of hydrogen bonding in the solvent (i.e., water) more than the products do. 22. Estimate Δ for the following reaction (bond dissociation energy values are provide Bond Dissociation Energies 100 kcal/mol kcal/mol 362 kcal./mol 46.0 kcal/mol -22 kcal/mol -30 kcal/mol e) -362 kcal./mol R 92 kcal/mol 2 2 (π-bond only) 66 kcal/mol

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