Chemistry 210 Organic Chemistry I Winter Semester 2002 Dr. Rainer Glaser

Transcription

1 Chemistry 210 rganic Chemistry I Winter Semester 2002 Dr. Rainer Glaser Examination #2 Molecular rbitals, Intra- and Intermolecular Bonding, Conformational Theory of Alkanes & Cycloalkanes. Friday, February 22, 2002, 9:00-9:50 ame: Question 1. Geometry & ybridization. (ews, VC #2) 20 Question 2. Molecular rbitals of Ethene. (WD) 20 Question 3. Intermolecular Interactions. (VC #2) 20 Question 4. omenclature of Alkanes. 20 Question 5. Conformations of Cycloalkanes. (VC #3) 20 Total 100 1

2 Question 1. Geometry & ybridization. (20 points) (a) The Molecule of the Week of the American Chemical Society for the week of 2/18/2 is efavirenz. The citations is as follows: The FDA just approved a once-daily tablet of efavirenz for the treatment of IV. This reverse transcriptase inhibitor is typically prescribed in combination with a protease inhibitor. (9 points) F 3 C Length of the C C triple bond (include units)? ybridization of the C-atom that carries the -atom? umber of sp-hybridized C-atoms? umber of lone pairs on -atom? Approximate value of the F C F angle? Is this compound aromatic? (b) ydrogenperoxide,, contains -hybridized -atoms. (6 points) Complete Lewis Structure Provide approximate values Draw ewman Projection angle: dihedral angle: (c) Diimine, =, contains -hybridized -atoms. (5 points) Complete Lewis Structure of trans-diimine Complete Lewis Structure of cis-diimine Provide approximate values angle: dihedral angle in cis-diimine: 2

3 Question 2. Molecular rbitals of Ethene. (20 points) Ethene has σ- and π-bonds. The σ-bonds are conveniently described by valence bond theory using (abbreviated As) at the C-atoms. ence, the C bonds are formed by overlap between a A of and an (sp, sp 2, sp 3 ) A on C and the C C σ-bond is formed by overlap between two (sp, sp 2, sp 3 ) As of the C-atoms. (4 points) The π-ms shown are formed by LCA of the carbon p-as that are perpendicular to the plane of the molecule and the colors indicate different orbital signs. (2 points each item) Lobe Diagram: Lobe Diagram: umber of node planes: If there are any, then draw them in the top picture and also in the lobe diagram. ow many electrons occupy this molecular orbital in the ground state? ow many electrons occupy this molecular orbital in the lowest excited state? umber of node planes: If there are any, then draw them in the top picture and also in the lobe diagram. ow many electrons occupy this molecular orbital in the ground state? ow many electrons occupy this molecular orbital in the lowest excited state? 3

4 Question 3. Intermolecular Interactions. (20 points) (a) What is the primary interaction responsible for hydrogen-bonding? (2 points) (a) permanent dipole / permanent dipole (PP) (b) induced dipole / permanent dipole (IP) (c) temporary dipole / permanent dipole (TP) (d) induced dipole / induced dipole (II) (e) temporary dipole / induced dipole (TI) (b) From the Visualization Center: Draw a hydrogen-bonded cyclic trimer of ammonia. Show all lone pairs. Indicate the hydrogen bonds by dashes. Indicate who is the hydrogen bond donor and who is the hydrogen bond acceptor. Indicate the polarity of the bonds using partial charges δ + and δ -. (8 points) Cyclic Ammonia Trimer (c) Complete the Lewis-Kekule structure of the guanine-cytosine base pair by adding all lone pairs. Then, using dashed lines, indicate the hydrogen bonds that bind these two DA bases. (4 points) (d) Decane (does, does not) mix with water. Decane would (love, hate, be indifferent) to mix with water because its (PP, IP, TP, II, IT) interactions with water are (stronger, weaker, about the same) than/as (PP, IP, TP, II, IT) interactions between decanes. (6 points; 2 p. for the first blank, 1 p. for the others) 4

5 Question 4. omenclature of Alkanes. (20 points) ame for 1 (3 points): ame for 2 (3 points): ame for 3 (3 points): Molecular formula for 3 (1 point): Empirical formula for 3 (1 point): Draw a small circle around every secondary carbon atom in molecule 3. (2 points) Draw a small square around every 4º carbon in molecules 2 and 3. (2 points) Provide a stoichiometric equation for the combustion of compound 3 (2 points): Draw the structure of bicyclo[4.4.0]decane (3 points): 5

6 Question 5. Conformations of Cycloalkanes. (20 points) (a) Basics about Cyclohexane and Cyclopropane. (9 points) ybridization of carbon in cyclohexane? Approximate length of the C-C bonds in cyclohexane in Angstrom? What is the value of the C-C-C bond angles in cyclohexane? What is the value of the total ring strain of cyclohexane in kcal/mol? umber of CC gauche conformations in the chair form of cyclohexane? umber of eclipsed conformations in the boat form of cyclohexane? umber of axial -atoms in the most stable conformation of methylcyclohexane? What is the value of the total ring strain of cyclopropane in kcal/mol? umber of staggered conformations in cyclopropane? (b) Draw the ewman projection of the dibromocyclohexane shown. Look down the C1-C3 and C17- C13 bonds, that is, C1 and C17 are close to you. (4 pts) (c) The schematic energy diagram is shown for the ring-flipping of cyclohexane. Provide the energy values in kcal/mol (at arrows) and indicate which points correspond to which conformations. (7 points) E 6