311Exam1Key2014 - CHE 311 EXAM 1(CH 1-4 KEY Answers in BOLD...

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Unformatted text preview: CHE 311 EXAM 1 (CH. 1-­‐4) KEY Answers in BOLD RED Multiple Choice (60%; 2% each) Clearly mark the letter of the BEST answer to each question clearly on your answer sheet. Thanks! 1. A triple bond between atoms will involve ____ shared electrons. A. six B. four C. three 2. Based upon general electronegativity trends, which of these single bonds will be LEAST polar? A. C–Br B. C–F C. C–H D. C–O 3. The species diazomethane (a common name) is a CH2 group attached to N2 this way: H2C=N=N: , with two lone pairs on the right N and none on the middle one. The formal charges on C, N, N (in order) are: A. 0, +1, –1 B. +1, 0, –1 C. 0, 0, 0 D. 0, –1, +1 4. Comparing the four choices to the leftmost structure below, which of them is a constitutional isomer of it? B is D. eight ¨ A.######################################B.#########################C.#######################################################D. 5. Which of these elements will NOT be able to exceed the octet rule? A. S B. P C. Br 6. All of these substances may be classed as Lewis acids; which cannot also be a Brønsted-­‐Lowry acid? A. H2S B. BF3 C. HF D. NH4+ 7. In the typical hydrocarbon molecules’ structure, C has a tetrahedral geometry, indicating _________ hybridization. A. no B. sp C. sp2 D. sp3 8. In hydrocarbons with a DOUBLE bond between two C atoms, which is NOT true? A. the C-­‐to-­‐C bond is longer than C-­‐C single bonds B. the C-­‐to-­‐C bond is stronger than C-­‐C single bonds C. rotation around the C=C bond is restricted D. the angles around the C=C are about 120° 9. Which of the following substances contains an alkyl group that has the common name “isopropyl”? answer D D. O 10. Br A.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%B.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%C.%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%D. Br Br The correct IUPAC name for the alkane whose structure is shown at the right is: A. 2-­‐Ethyl-­‐3-­‐methylpentane B. 3,4-­‐Dimethylhexane C. 1,2,3-­‐Trimethylpentane D. 2-­‐Ethyl-­‐3,4-­‐dimethylpropane 11. Refer to the structures shown in question 9. In which one or ones is the Br at a secondary carbon position? A. A & D B. A only C. B & C D. B only 12. The formula C4H8Cl2 has many isomers. Name the one in which all the carbons are methylene groups: A. 1,2-­‐dichlorocyclobutane B. 2,3-­‐dichlorobutane C. 1,4-­‐dichlorobutane D. 2,2-­‐dichloro-­‐2-­‐methylpropane 13. The process by which the hydrocarbons in petroleum are converted to smaller alkanes and alkenes is called A. division B. cracking C. reforming D. octaning 14. Combustion which completely converts alkanes to CO2 and H2O allows us to determine that the most stable of the C7H16 alkanes is: A. 2,2,3-­‐Trimethylbutane B. Heptane C. Methylcyclohexane D. 2,3-­‐Dimethylpentane 15. Which of these strain types includes the others within it? A. torsional B. angle C. van der Waals 16. In your textbook’s description of the energies related to conformations, the __________ form is called the transition state for the ___________ form. A. staggered; eclipsed B. eclipsed; staggered Br D. steric CHE 311 Exam 1 17. Page 2 The Newman projection of the most stable conformer of 2-­‐methylbutane is: A (all look down the C2-­‐C3 axis) H CH3 CH3 H H H H H H A.##################################################B.###############################################C.####################################################D. H CH3 H3 C CH3 CH3 CH3 H3C H CH3 H3C H CH3 H CH3 H 18. Which type of strain is still significantly present in a chair cyclohexane structure? A. diaxial B. angle C. torsional D. eclipsing 19. The most stable chair conformation of cis-­‐3-­‐Chlorocyclohexan-­‐1-­‐ol has: (note –Cl is a bit larger than –OH) A. both groups axial B. –OH axial, -­‐Cl equatorial C. –Cl axial, -­‐OH equatorial D. both groups equatorial 20. 21. Here are four conformers of trans-­‐1,2-­‐dimethylcyclohexane. Which is the most stable and is correctly drawn? C H H CH3 H H3C H H H H H H H H H H H H H H H H H H CH A.##################################################B.###############################################C.####################################################D. H 3 H H H CH3 H H CH3 H H H H H H H H CH3 CH H H H H 3 CH3 H The bicyclic ring shown at the right would be properly named using the IUPAC rules if it was called: A. Bicyclo[1.1.3]heptane B. Bicyclo[3.3.5]heptane C. Bicyclo[3.1.1]heptane D. Bicyclo[1.1.3]pentane 22. Naturally-­‐occurring heterocyclic molecules include those having all of the following elements except for: A. S B. B C. O D. N 23. Bonds between C and F are not as polar as expected because: A. C is quite electronegative B. F is not that electronegative C. the bond is so long D. the bond is so short 24. F has a mass of 17; so does –OH, but alcohols are much more polar than alkyl fluorides of the same mass. Why? A. alcohols contain water B. C–F bonds are nonpolar C. alcohols hydrogen bond D. alcohols are more dense 25. Which of these is most likely to react with conc. HBr by an SN1 mechanism? A. 2-­‐butanol B. 1-­‐butanol C. 2-­‐Methyl-­‐1-­‐propanol 26. Among the reagents that might be used to convert 1-­‐propanol to 1-­‐chloropropane, the best one to use is A. conc. HCl B. SOCl2 C. NaCl + H2SO4 D. CaCl2 + heat 27. In reacting a primary alcohol with HBr, the slow step of the process will be: A. loss of H2O B. Br– displacing H2O C. Br– attack on a carbocation D. –OH protonation 28. Which is a secondary alcohol? A. 2-­‐Methyl-­‐1-­‐propanol B. 1-­‐butanol 29. All free radical propagation steps A. form as many radicals as they use B. form more radicals that they begin with C. produce less radicals 30. Bromination of 2-­‐Methylbutane by a free radical mechanism will primarily produce: A. 1-­‐Bromo-­‐2-­‐methylbutane B. 1-­‐Bromo-­‐3-­‐methylbutane C. 2-­‐Bromo-­‐3-­‐methylbutane D. 2-­‐Bromo-­‐2-­‐methylbutane C. 2-­‐butanol See the next page for the problems D. 2-­‐Methyl-­‐2-­‐propanol D. 2-­‐Methyl-­‐2-­‐propanol CHE 311 Exam 1 Page 3 Problems (40%; 20% each) I. Draw out both chair conformations of the following disubstituted cyclohexane. CIRCLE one if it is more stable. [note that Br and methyl are about the same size] Br CH3 H H H H Br H H H H H H H H H H H Br H H H H H CH3 CH3 Both)equatorial)00)more)stable Both)axial)00)very)bad II. Draw the steps in the mechanism of the substitution shown below. BE SURE to clearly draw any key intermediates or transition states in this mechanism, and label the slow step (RDS). Br OH HBr –&H2O H Br OH OH2 OH2 – H2O Slow step (RDS) Br Br ...
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