Note: You must have your answers written in pen if you want a regrade!!!!

Transcription

1 NAME (Print): SIGNATURE: hemistry 310M/318M Dr. Brent Iverson 1st Midterm ctober 4, 2007 Please print the first three letters of your last name in the three boxes Please Note: This test may be a bit long, but there is a reason. I would like to give you a lot of little questions, so you can find ones you can answer and show me what you know, rather than just a few questions that may be testing the one thing you forgot. I recommend you look the exam over and answer the questions you are sure of first, then go back and try to figure out the rest. Also make sure to look at the point totals on the questions as a guide to help budget your time. Note: You must have your answers written in pen if you want a regrade!!!!

2 onor ode The core values of the University of Texas at Austin are learning, discovery, freedom, leadership, individual opportunity, and responsibility. Each member of the University is expected to uphold these values through integrity, honesty, trust, fairness, and respect toward peers and community. (Your signature)

3 Page Points Total (26) (16) (15) (20) (20) (26) (22) (27) (14) (35) (28) (20) (12) (12) (5) (298) W T Score

4 Pg 1 (26) 1. (8 points) What is the most important question in rganic hemistry? 2. (6 pts each) For the following molecular formulas, draw complete Lewis line structures in which all atoms (even atoms) are drawn, lines are used as bonds, and all lone pairs are drawn. A) ( 3 ) B) 2 2 ) N( 3 ) 2

5 Pg 2 (16) 3. (4 pts each) Provide an acceptable IUPA name for the following molecules. You can ignore R and S for this one. A) B) ) D)

6 Pg 3 (15) 5. (5pts each) For the following IUPA names, draw the appropriate line angle drawing (you can ignore R and S for this). A) 4-tert-butyl -5-ethyl-2-methylheptane B) trans-1-methyl-3-(1-methylpropyl)cyclopentane ) trans-1-sec-butyl-3-methylcyclopentane

7 Pg 4 (20) 6. (5pts each) The following molecules are best represented as the hybrid of contributing structures. Draw the second important contributing structure in the space provided, including all lone pairs and formal charges. For the structure on the left, use arrows to indicate the movement of electrons to give the structure you drew. Finally, if one of the two contributing structures makes a dominant (major) contribution to the resonance hybrid, draw a circle around the dominant (major) contributor. You might want to read these directions again to make sure you know what we want. A. B.. N N D.

8 Pg 5 (20) 7. (10 pts each) The following molecules are best represented as the hybrid of three contributing structures. Draw the second and third important contributing structures in the spaces provided, including all lone pairs and formal charges. For the two structures on the left in each problem, use arrows to indicate the movement of electrons to give the structures you drew. There is no need to draw any circles around any of these contributing strucures. You might want to read these directions again to make sure you know what we want. A. B. N Ribbit

9 Pg 6 (26) 8. (2 pts each) Fill in each blank with the word or words that best completes the sentences. For organic chemistry, it is best to think of electrons as. According to the approach, the atomic orbitals on each atom are combined (hybridized) first, and bonds are derived from overlap of hybridized orbitals. It is best to think about all bonding in molecules as being derived from the overlap of hybridized orbitals and all bonding as being derived from overlap of unhybridized 2p orbitals. Alkanes "stick" together due to so-called forces, which are the weakest of the electrostatic interactions (i.e. charge-charge interactions) and are the result of attraction between (induced) dipoles among adjacent molecules. 9. (1 pt each) For the following molecules, write the hybridization state of each atom indicated by the arrow. N N

10 Pg 7 (22) 9. (2 pts each) Describe each bond indicated with an arrow as the overlap of orbitals. For example, an answer might be! sp 3 -sp 3.

11 Pg 8 (27) 10. (3 pts each) For the following molecules, use the dipole moment symbol to show the direction of the molecular dipolemoment in all molecules that have an overall molecular dipole. l l l l l l For the molecule above, give the molecular dipole for the conformation shown. 11. (3 pts each) Put a check mark under all the types of strain that explain(s) the following statements: Angle strain Torsional strain Steric strain A) Eclipsed ethane is less stable than staggered ethane because of: B) Gauche butane is less stable than anti butane because of: ) yclopropane has more strain than cyclopentane due to: D) yclobutane has more strain than cyclohexane due to: E) For cyclohexane, an axial methyl group has more strain than an equatorial methyl group due to:

12 Pg 9 (14) 12. (7 pts each) For the following cyclohexane derivatives, draw the two alternative chair conformations. If there is a difference in stability, draw a circle around the more stable conformation. A) B)

13 Pg 10 (35) 13. (7 pts) For the following molecule of glucose, draw both alternative chair conformations. ircle the one that is more stable. This is called!-d-glucose (2 pts each) For the following molecules, label each chiral center with an asterisk (*) l Br l F Br 2 N3 3 2 N3 3 3 l l l 3

14 Pg 11 (28) 15. (3 pts) Label each chiral center as "R" or "S". Br Br l l 3 l 3 l 3 3 Br Br (5 pts each) For the following conformations, draw the Newman Projection from the perspective indicated by the eye of the observer 3 3 l 3 l 3 3 3

15 Pg 12 (20) 17. (14 pts) The following molecule (2,3-dimethylbutane) can be described by three different Newman projections of staggered conformations as the central bond is rotated. Draw all three different Newman projections, and draw a circle around the one with the lowest energy (least strain). central bond (2 pts each) For the following molecule, write in the box whether the indicated carbon atom is primary, secondary, tertiary or quarternary

16 Pg 13 (12) 19. (12 pts) The following three structures have delocalized pi systems that can best be described by the molecular orbital approach based on the overlap of three 2p orbitals. At the bottom of the page are three different molecular orbital diagrams, labeled as "A", "B",and "". Underneath the structures in the boxes, write the letter ("A", "B", ""or "D, none of the above") that most accurately describes that molecule's delocallized pi system. N A Three 2p orbitals Three pi molecular orbitals B Three 2p orbitals Three pi molecular orbitals Three 2p orbitals Three pi molecular orbitals D None of the above

17 Pg 14 (12) 20. (12 pts) Save this until the end. A series of alkanes are listed along with their boiling points A) From the data listed, draw two different conclusions regarding how boiling point changes with structure. B) From the data listed, predict (within 5 ) the boiling point of heptane. ) From the data above, estimate approximately how much increase in boiling point there is for each additional group in an unbranched alkane.

18 Pg 15 (5) 20 (cont.). (5 pts) Save this until the end. A series of alkanes are listed along with their boiling points. Boiling point 106 Melting Point 104 Boiling point 126 Melting Point -57 D) The boiling point of 2,2,3,3-tetramethylbutane is 106, in line with the other alkanes. owever, 2,2,3,3-tetramethylbutane is a solid at room tempterature, not a liquid like the others, because it has a melting point of 104. It is only a liquid for the span of 2!! For comparison, octane is only a solid below -57. Briefly explain why 2,2,3,3-tetramethylbutane exhibits this unsual behavior.