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318N CH Name: Homework # 3 Spring 2008 Due: TUESDAY 02-19-08 Please follow the HW Guidelines as posted on Blackboard. 1. Name each of the following molecules in accord with the IUPAC system of nomenclature. (a) 3-ethylpent-1-ene (b) Cl Cl 1,1-dichlorobut-1-ene (c) O O (Z)-1,2-dimethoxyprop-1-ene (d) 1-ethyl-6-methylcyclohex-1-ene CH 318N Name: Spring 2008 2. Determine the molecular formulas corresponding to each of the following structures. For each structure, calculate the number of degrees of unsaturation from the molecular formula and evaluate whether your calculations agree with the structures shown. (a). C7H14 Hsat=1 (b) C5H6 Hsat=3 (c) O C5H8O Hsat=2 (d). C10H14 Hsat=4 CH 318N Name: Spring 2008 3. Two IR spectra are shown. One is the spectrum of cyclohexane, and the other is the spectrum of cyclohexene. Identify them, and explain your answer. (a) cyclohexane (b) cyclohexene While there are many differences, the peaks at 1650 cm-1 and 3000 cm-1 in spectrum (b) correspond to a C=C and =C-H stretch, respectively. CH 318N Name: 4. The mass spectrum (a) and the infrared spectrum (b) of another unknown hydrocarbon are shown. Propose at least two possible structures. Spring 2008 These are the only two distinct hydrocarbons that fit both spectra. The M+ = 70 requires a formula of C5H10. The peak at m/z = 55 corresponds to the loss of a methyl group. The IR corresponds to an internal alkene due to the presence of 1660 cm-1 and 3000 cm-1 stretches as well as the lack of peaks at 890-990 cm-1. A compound with the above formula, an internal alkene, and a likely methyl group fragmentation could only one be of the two above structures. Note: You cannot distinguish stereoisomers using these spectra, so the cis isomers of the above compounds are also possibilities. (2-methyl-2butene happens to be correct) CH 318N Name: Spring 2008 5. Explain in detail the differences between the mechanisms giving rise to the following two experimental results. CH3 Cl Na OCH2CH3 CH3CH2OH CH(CH3)2 CH(CH3)2 100% CH3 CH3 Na OCH2CH3 Cl CH(CH3)2 CH3CH2OH CH3 + CH(CH3)2 25% CH3 CH(CH3)2 75% When E2 eliminations occur in cyclohexanes, the leaving group and the -H to be removed must have a 1,2-trans diaxial relationship. So, first, draw the two possible chair conformations for each starting compound, and analyze the one in which the Cl leaving group is axial. CH 318N Name: Spring 2008 6. On the following alkenes, fill in the remaining hydrogens and describe the specific name, if there is one, of the NMR coupling relationship each would have with the hydrogen shown in bold. Use the following notation: identical (I), vicinal (V), geminal (G), allylic (A), long-range (LR) or none (N). a) (A) (LR) (A) H H H H H (G) H (LR) (LR) H H (V) b) (LR) (LR) H (A) (LR) H H (LR) H H H H (N) H (V) (N) H (LR) H (LR) H H (N) CH 318N Name: Spring 2008 Recommended problems: Chapter 11 Exercises: 1, 2, 3, 4, 5, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 21, 22 Chapter 11 Problems: 26, 27, 28, 30, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 45, 48 Note: Please also practice the spectroscopy/spectrometry problems available online as discussed in class. Since you will be responsible for recognizing patterns, extensive practice is essential!

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