CHAPTER 4 HW: ALKANES

Transcription

1 CAPTER 4 W: ALKANES CLASSES OF CARBON 1. assify each carbon atom pointed to below as 1, 2, 3 or Draw an alkane that contains only: 1 and 4 carbon atoms 2 carbon atoms 1 and 2 carbon atoms 1 and 3 carbon atoms EAT OF COMBUSTION DATA 3. The combustion data for propane and cyclohexane is shown in the table below. Explain why it is incorrect to say (based on the data) that cyclohexane is kcal/mol ( ) higher in energy than propane. D comb (kcal/mol) + 5 O 2 à 3 CO O O 2 à 6 CO O Page 1

2 4. Use the heat of combustion data below to determine which organic compound is lower in energy, and by how much. Support your calculation with a diagram. D comb (kcal/mol) + 25/2 O 2 à 8 CO O /2 O 2 à 8 CO O ALKANE AND ALKYL ALIDE NOMENCLATURE 5. (Multiple Choice) Which is the correct IUPAC name for each compound? 2-methylbutane 2,2-methylbutane 2,2-dimethylbutane 2-dimethylbutane 3-bromo-1-chlorobutane 2-bromo-4-chlorobutane 1-chloro-3-bromobutane 1-chloro-4-bromopentane 1,1-dimethyl-2-iodocyclopentane 2-iodo-1,1-dimethylcyclopentane 1-iodo-2,2-dimethylcyclopentane 2,2-dimethyl-1-iodocyclopentane I Page 2

3 6. Give the IUPAC name for each compound. I F I 7. Each compound below is named incorrectly. Give the correct name for each. 2-propyl-5-ethylheptane 3-t-butylhexane Page 3

4 NEWMAN PROJECTIONS 8. Determine which Newman projection in each set is lower in energy. Explain your answers. a. C 3 C 3 b. C 3 C 3 c. C 3 C 3 9. Draw the following Newman projections of: exane, looking down the C 1 -C 2 bond exane, down the C 2 -C 3 bond exane, down the C 3 -C 4 bond 2,2-dimethylheptane, down the C 2 -C 3 bond 10. Draw the line structure of each compound, shown below in a Newman projection. C 3 C 3 C 2 C 3 C 2 C 3 Page 4

5 11. Consider the compounds 1-bromopropane and ethylene glycol (OC 2 C 2 O). a. Draw the anti and gauche conformations of both compounds. Anti 1-bromopropane Gauche 1-bromopropane Anti ethylene glycol Gauche ethylene glycol b. Explain why the anti conformation of 1-bromopropane is lower in energy than the gauche conformation. c. Ethylene glycol is unusual in that the gauche conformation is lower in energy than the anti conformation. Offer an explanation. RING STRAIN 12. It is approximated that each C 2 group in a linear alkane has a D comb of kcal/mol. Cyclooctane has an experimental!d comb of kcal/mol. a. Calculate the amount of ring strain in cyclooctane. b. Compared to other ring systems, would you classify this amount of strain as high, moderate or low? Page 5

6 13. Describe two sources of ring strain in cyclobutane. 14. Explain why 1,1-dimethylcyclopropane has more ring strain than ethylcyclopropane. int: draw Newman projections. 15. Which should release more energy with combustion: cyclopentane or methylcyclobutane? Explain. Include a diagram with your answer. Page 6

7 CAIR CONFORMATIONS 16. Practice drawing chair conformations: Instructions Drawing of chair a. Draw in the equatorial C- bond (using the correct angle) on the carbon atom labeled #1. 1 b. Draw all axial and equatorial C- bonds for the front 3 carbon atoms of both chairs. Draw the equatorial C- bonds using the correct angles. c. Draw all axial and equatorial C- bonds for the back 3 carbon atoms of both chairs. d. Draw 1,2-dibromocyclohexane with both bromine atoms axial. e. Draw 1,3-dimethoxycyclohexane with one group axial and one group equatorial. ( Methoxy is OC 3 ) f. Draw an isopropyl group equatorial on the dot. Then perform a ring flip and draw the second chair conformation beside it. g. Draw a fluoro group axial on the dot. Draw the second chair conformation. h. Draw a tert-butyl group axial on the left dot and a methyl group equatorial on the right dot. Draw the second chair conformation. i. Draw an iodo group equatorial on the dot. Draw the second chair conformation. Page 7

8 AXIAL AND EQUATORIAL POSITIONS 17. Consider ethylcyclohexane. a. Draw the Newman projections of axial-ethylcyclohexane and equatorial-ethylcyclohexane. b. Why is axial-ethylcyclohexane higher in energy than equatorial-ethylcyclohexane? 18. The two chair conformations of Compound M are equal in energy, while the two chair conformations of Compound N are different energy. Explain. M N 3 C C Explain why a tert-butyl group has a larger A value than an ethyl group. Page 8

9 CAIR TO CAIR INTERCONVERSIONS ( RING FLIPS ) 20. For each compound, perform a ring flip and draw the second chair conformation. Then determine which chair is lower in energy. (Use a table from lecture for A values.) C 3 C 3 C 2 C 3 OC 3 I OC 3 O Page 9

10 21. In each set, determine which isomer is lower in energy, and explain your answer. (Remember that cyclohexane rings are not flat!) a. b. C 2 C 3 C 2 C 3 C 2 C 3 C 2 C 3 c. C 2 C 3 C2 C 3 C 3 C 3 C 3 C3 d. C 3 C 3 C 3 C 3 C 3 C3 e. C 3 C 3 Page 10

11 STEREOISOMERS 22. Define and give an example of: a. Constitutional Isomers b. Stereoisomers 23. Convert each chair into a line structure (hexagon), using dashed and wedged bonds. O O C 3 O O 24. Are the following statements concerning the molecules below true or false? iefly explain each answer. a. Both molecules are cis. b. A cis isomer always has the groups axial-axial or equatorial-equatorial. Page 11

12 25. Give the IUPAC name for each compound, including cis/trans designations. C 3 C 3 C 3 C 2 C 3 C 2 C 3 I C 3 F 26. assify the relationship between each pair as constitutional isomers, stereoisomers, identical, or not isomers. Pair O O O O Relationship Pair Relationship O O Pair C 3 C 3 Relationship Page 12