_________________________ Name: Chemistry 231 Fall 2007 Exam 2 Before beginning: 1. There are a total of 5 pages to this exam containing questions A-K. Check to make sure that you have a complete exam.
2. Clearly print your name on the blank at the top of this page. Clearly print your name (last name, first name) at the top of the page on the back of the exam.
3. Carefully read all instructions for each question and supply the requested information to the best of your ability. Some questions may have more than one part. ** Please, ask for clarification if you do not fully understand a question ** This is a closed book exam. You may only use the material provided within the exam booklet. Keep your books and notes out of sight and your eyes on your own paper. A B C D E F G H I J K 6 2 4 4 4 4 4 4 4 2 12 _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____
Subtotal Adjust Total (50 pts)
_____ _____ _____
Exam 2 Percentage: _______
Current Course Percentage: _______
A. (6 pts) Provide an acceptable IUPAC systematic name for each of the following structures, clearly indicating stereochemistry where appropriate.
Cl CH2CH(CH3)2 4-ethyl-2-methyl-5-propylnonane cis-1-chloro-5-isobutylcyclooctane
Br (R)-6-bromo-2,2-dimethylheptane
B. (2 pts) ) Provide a clear structural representation for the following IUPAC systematic name, clearly showing stereochemistry where necessary. (R)-2-fluoro-2,4-dimethylhexane
F
C. (4 pts) Consider the molecule 1-bromo-2-methylpropane. Draw two different staggered Newman projections on the framework provided below, siting down the C1-C2 bond. Circle the Newman projection that is lower in energy. Briefly explain why the Newman projection that you chose is lower in energy.
Br CH3 H H CH3 H H H
Br CH3 H CH3
Explanation: The second structure has less steric strain with only 1 gauche staggered interaction between the larger groups (CH3's and Br), while the first structure has 2 gauche staggered interactions.
D. (4 pts) Draw the two chair conformations of the structure below on the chair structures shown. Circle the more stable conformation.
CH3
CH3
CH3
Cl
Cl
Cl
CH(CH3)2
E. (4 pts) Below is a potential energy diagram and four Newman projections for the rotational conformations of 2-methylbutane:
a) The Newman projection that corresponds to the position labeled 4.8 on the energy diagram is (circle the letter corresponding to your choice): A B C D
b) The Newman projection corresponding to the position labeled 4.9 on the energy diagram is (circle the letter corresponding to your answer): A B C D
F. (4 pts) Consider the following two set of four substituent groups. For each set, indicate the highest (H) and lowest (L) priority groups for assigning R, S-configurations by placing the appropriate letter below the structure. Each set of four should have only one H and one L indicated
CH2C CH L H
CH(CH3)2 H CH2CH2F CH2C(CH3)3 L CH2CH2OCH3
CH CH2
C(CH3)3
G. (4 pts) Indicate the number of stereocenters contained in each of the following by structures placing the appropriate number on the blank below the structure.
H3C H3C H3C CH3 CH3 O O NO2
HO 7
OH
CH2COCH3 3
H. (4 pts) Assign R or S configurations to the structure below by placing the appropriate letter on the blanks provided for each stereocenter.
OH HO HO H S H3C Br H CH3 S R H HO C C C O O H CH2OH R
I.
(4 pts) Determine whether the following pairs of molecules are constitutional isomers (C), enantiomers (E), diastereomers (D), identical (I) or not isomers (N). Place the appropriate letter on the blank below the structures.
CH3 H H 3C H I Br OH HO H H CH3 Br CH3 OH D OH H H CH3 OH OH CH3
Cl Cl
H H C
Cl H
Cl H HO H
Cl Cl E
H OH
J. (2 pts) Briefly explain the following why cis-1,2-dibromocyclobutane has a larger heat of combustion (i.e. is less stable) than trans-1,2-dibromocyclobutane. Be brief, but specific using appropriate terminology. There is less steric strain with the two methyl groups on opposite faces of the cyclobutane ring (trans) than when they are adjacent to each other (cis).
K. (12 pts) Circle the best response for each of the following items. 1. Which of the following constitutional isomers of formula C 5H10 would produce the most heat per carbon atom on complete combustion with oxygen gas? a. b. c. d. e.
2.
ethylcyclopropane trans-1,2-dimethylcyclopropane methylcyclobutane cyclopentane since they are all constitutional isomers, they all would have the same heat of combustion
Which of the following statements correctly describes the typical bonding of carbon, nitrogen, and oxygen in organic molecules?
Oxygen participates in 2 covalent bonds and has 2 lone pairs of electrons. Nitrogen participates in 2 covalent bonds and has 1 lone pair. Carbon participates in 4 covalent bonds and has no lone pairs. Oxygen participates in 2 covalent bonds and has 2 lone pairs of electrons; nitrogen participates in 2 covalent bonds and has 1 lone pair. e. Oxygen participates in 2 covalent bonds and has 2 lone pairs of electrons; carbon participates in 4 covalent bonds and has no lone pairs. a. b. c. d. 3. Convert the following skeletal formula to a condensed formula. a. b. c. d. e. CH3CH2CH(CH3)2CH(CH2CH3)CH(CH3)2 CH3CH2CH(CH3)CH(CH2CH3)CH(CH3)2 CH3CH(CH3)CH(CH2CH3)CH(CH3)2 a and b a and c
4. Which statement best describes the orbitals that are used to form bonds in the cation below? a. The bond between the two carbon atoms is formed between two sp2 hybridized atoms. b. The bond between the C and N is formed between an sp2 hybridized C and an sp hybridized N. c. The bond between the two carbons is formed between one sp3 hybridized C and one sp hybridized C. d. The lone pair of electrons on N is in an sp hybridized orbital. e. None of the statements are correct. 5. Which of the following species is the strongest base? a. CH3b. NH2c. Cld. OHe. I-
6. Which functional groups are present in the molecule given below? a. b. c. d. e. Aldehyde, amine, ketone Aldehyde, amine, carboxylic acid Aldehyde and amide Aldehyde, amine, ester Amide and ketone