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1 hem 0 Midterm Winter, 08 Beauchamp ame Key Problems Points redit. Functional Group omenclature ( large structure) 0. Resonance, Formal harge, Arrows 8. Properties of Atoms, Logic Arguments of rganic hemistry (ionization potential, Z eff, radii, electronegativity, etc.) 0. Types of Isomers, Degrees of Unsaturation. Forces of Interaction and ysical Properties. yclohexane onformations, ewman Projections 0 7. ewman Projections, onformational Energies 8. D Structure, Resonance, ybridization, Angles, Shapes () 0 9. Stereochemical Analysis 0. D Lewis Structures () 0. Functional Groups, ames, Degrees of Unsaturation or Special Types of arbons and Substituents Total 9 This is a long exam. It has been designed so that no one question will make or break you. The best strategy is to work steadily, starting with those problems you understand best. Make sure you show all of your work. Draw in any lone pairs of electrons, formal charge and curved arrows to show electron movement where appropriate. Do your best to show me what you know in the time available. Excuses will always be there for you, opportunity won t.

2 . Provide an acceptable name for the following molecule. nly specify R and S where shown as D. (0 pts) 9 8 7E 7 S highest priority = ester S l S-mercapto--oxo--phenyl--benzyl--(-methylpentyl)-8-cyano-9-hydroxynon-7E-enyl chloro--methoxycarbonyl- -(,-dimethylbutoxy)-s-amino-r-bromo-7-(,-dimethyl--formyl--pentylcyclohex--enyl)-8-(-amido- -octylcyclonona-z,9z-dienyl)--nitro--oxododec-z-en-9-ynoate Z S R 9Z Z. Indicate all formal charges present in the following structures. Assume all electrons are shown as lines or dots. If other reasonable resonance structures are possible, draw the best other resonance structure using the proper arrow conventions. Indicate which resonance structure is better or if they are equivalent. (8 pts) Similar in stability, negative is on nitrogen in both resonance structures. The first resonance structure is better because it has more bonds and full octets. The second resonance structure is better because it has the positive charge on nitrogen rather than oxygen. Both resonance structures have an extra bond and full octets. There is an acceptable rd resonance structure with + on carbon, but it has fewer bonds and an incomplete octet.

3 . a. Which atom has the higher first ionization potential and why? (a or l) (0 pts) a and l are in the same row. a has a Z eff of + and l has a Z eff of +7, so l will hold on to its electrons much tighter than a and require more energy to strip an electron away. IP (a) = 8 kcal/mole and IP (l) = 00 kcal/mole b. Which neutral atom has the larger atomic radius and why? (Si or Ar) Silicon and argon are in the same row. Si has a Z eff of + and Ar has a Z eff of +8, so Ar will hold on to its electrons much tighter than Si. This should contract the electron cloud making the radius of argon (r Ar = 70 pm) smaller than silicon (r Si = 0 pm). c. Which anion has the larger radius and why? ( - or - ) Both - and - are in the same row and have a full n= shell (full octets). xygen has Z eff of + and has a Z eff of +, so will hold on to its electrons tighter than. The radius of oxide (r - = pm) is smaller than nitride (r - = pm) d. Which cation has the larger radius and why? (Mg + or Al + ) Both Mg + and Al + have lost all of their n= valence electrons and have a full n= shell (core electrons). Mg has Z eff of + and Al has a Z eff of +, so Al will hold on to its electrons tighter than Mg. The radius of Al + (r Al+ = 9 pm) should be smaller than Mg + (r Mg+ = 8 pm).. Use the formula to draw examples for each type of isomerism indicated. This will require that you draw at least two structures in each box to show these differences. What is the degree of unsaturation? ( pts) degree of unsaturation = () + + = one pi bond or one ring - = degree These conformers are cis/trans diasteromers, but achiral. skeletal isomers positional isomers conformational isomers amide R S S R amine ketone R R R S functional isomers diasteromers enantiomers

4 . a. aldol is a potent orally active central nervous system tranquilizer used in the treatment of psychoses. Peak plasma levels, when taken orally, are - hours (in the aqueous blood). ell membranes, on the other hand, are composed largely of alkane-like fatty acid chains. A decanoate ester prodrug was prepared to increase aldol s lifetime in the body. When injected intramuscularly its anti-psychotic activity lasted about month. Provide an explanation for its longer lifetime. ( pts) F F aldol l aldol decanoate l Typical membrane fat Answer: The alcohol of aldol makes it too water (blood) soluble and it is degraded as the blood passes through the liver by oxidizing enzymes, so it is excreted in the urine and/or feces. When the alcohol is esterified it is much less water (blood) soluble and gets stored in fatty tissue (membranes), where it is slowly released to the blood over a much longer time. Probably the ester is slowly hydrolyzed making it become more water soluble again, as the alcohol. b. Match the compounds with their boiling points with a brief explanation. ( pts) boiling points: o, o, 8 o, 80 o, 9 o, 0 o A B D E F MW = 88 g/mol Li MW = 8 g/mol MW = 88 g/mol MW = 87 g/mol MW = 88 g/mol MW = 8 g/mol Answer: Li is ionic with very strong forces of interaction, so its boiling point is extremely high (+ o ). arboxylic acid,, is next with both hydrogen bonding () and strong polarity (=) and has boiling point of + o. ext is the alcohol, A, which has hydrogen bonding () with boiling point of 8 o, followed by the ester, E, with polarity (=) and a boiling point of 80 o. Last are the two alkanes, having only dispersion forces. The linear hexane, F, has greater dispersion forces because more surface area of contact with its neighbors, boiling point = 9 o and the branched,-dimethylbutane, B, has the lowest boiling point of 0 o, due to less contact surface area with its neighbor molecules because of the branches.

5 . Draw all possible chair conformations of cis-- isopropyl--bromocyclohexane. Make the left most ring carbon and number towards the front. Show all axial and equatorial s in the first chair. Which conformation is more stable? Provide a reason for your answer. Draw a ewman projections of the least stable conformation using the and bonds to sight along. Point out any gauche interactions shown in your ewman projection. If the axial energy of an isopropyl is. kcal/mole and the axial energy of a bromo atom is 0. kcal/mole and a bromo/isopropyl gauche interaction is 0. kcal/mole, what is the ratio of the two conformations? Show your work. Sketch an energy diagram that shows how the energy changes with the conformational changes and estimate the ratio of the two conformations at equilibrium. (0 pts) a. one gauche = +0. K = 0.RT R = cal/mol-k T = 00 K one gauche = +0. axial = +0. (the longer - bond makes for a smaller axial energy) chair (more stable) one gauche = +0. cis--isopropyl--bromocyclohexane isopropyl = +. (larger has larger axial energy) chair (less stable) total = =. kcal/mole total = =.7 kcal/mole ) =.7 -. =. kcal/mole larger (higher axial energy) is axial in right structure so is positive and K eq <. b. ewman projection draw the least stable conformation, point out any gauche interactions with the substituent(s) one gauche in side chain = 0. i-pr Two gauche of i-pr with ring but we can only see one in the ewman projection. chair is less stable c. Energy diagram and relative percents (K =?) =. kcal/mole 9% 7% ) = +. kcal/mole =.7 kcal/mole K = 0.RT K = K = 0 -. K = 0.09 K = ()/() d. alculate an approximate difference between the two conformations. Use that value to estimate a K eq. (Assume R = cal/mol-k and T = 00 K.) Use energy values provided in the box. Show your work.

6 7. Use a ewman projection of the bond of -ethyl--phenylpentane to show the most stable conformation first. Rotate through all of the eclipsed and staggered conformations. Using the energy values provided in the table below, calculate the relative energies of the different conformations. Plot the changes in energy in the graph diagram provided. alculate a ratio of least stable to most stable based on values. int: Draw a D structure first and bold the bond viewed in your ewman projection, then decide your line of sight. ( pts) D structure - -ethyl--phenylpentane = = = = Me Approximate Eclipsing Energy Values (kcal/mole) Some were estimated by me. Me i-pr t-bu Me i-pr G K eq = 0 -.RT Approximate Gauche Energy Values (kcal/mole) Some were estimated by me. Me i-pr t-bu Me i-pr t-bu t-bu ethyl--phenylhexane ewman projections: 8 7 lowest PE Me gauche / = 0. gauche /Me = 0.0 gauche Me/ = 0.9 gauche / = 0. gauche / = 0. gauche / =. Total = Me. eclipsing Me/ =.7 eclipsing / =. eclipsing / =.7 Total =.9 highest PE / Me Me Me.0.7 Me Total = Total = Total =. Total = kcal/mole.9 kcal/mole. kcal/mole 7. kcal/mole.0 kcal/mole.7 kcal/mole 0 most stable least stable = =.7 ) = =.7 kcal/mole -700 K eq = 0 80 K eq = = = / 00 = (least) / (most)

7 8. Assume that all non-hydrogen atoms have a full octet, unless there is a positive charge on carbon. Draw a D Lewis structure for all reasonable resonance structures (include lone pairs and formal charge). Draw a D structure for the best resonance structure. Show bonds in front of the page as wedges, bonds in back of the page as dashed lines and bonds in the page as simple lines. Show orbitals and electrons for pi bonds and lone pairs with a circle around their electrons. Identify the hybridization, bond angles and descriptive shape for all numbered atoms. (0 pts) best resonance, negative on oxygen atom, draw this one in D D structure - Use the best resonance structure for the D structure and to fill in the following table. The best resonance has negative charge on the oxygen atom with the same number of pi bonds () in each of the resonance structures. Atom Shape ybridization Bond Angles # sigma bonds # pi bonds # lone pairs trigonal planar sp 0 0 linear sp 80 0 trigonal planar sp 0 0 trigonal planar sp 0 0 tetrahedral sp Explain the different - bond energies. Use structures in your explanation. Include any necessary lone pairs, formal charge, curved arrows, etc. What is the hybridization of oxygen in A and B? A 07 kcal/mole - resonance shows some double bond character between and The B - of B is sp, but A - of A is sp due to resonance with = functionality. Look at the second resonance structure B 9 kcal/mole normal single - bond

8 9. For the following set of Fischer projections answer each of the questions below by circling the appropriate letter(s) or letter combination(s). int: Redraw the Fischer projections with the longest carbon chain in the vertical direction and having similar atoms in the top and bottom portion. lassify all chiral centers in the first structure as R or S absolute configuration. ( pts)

9 0. Draw an acceptable Lewis structure (D) for the following formula. Show all single, double and triple bonds with one, two or three lines. Include all lone pairs of electrons as two dots. Include formal charge, if present at the atoms where present. (0 pts) has formal charge ring ( ) ( ) (l)( ) () l. Match the arrows with the terms. Some arrows may be associated with more than one term. ( pts). methyl. methylene. methine. primary. secondary. tertiary g a d g a d 7. quarternary 8. isopropyl 9. isobutyl 0. sec-butyl. t-butyl. neopentyl j e m b n k. vinyl f. allyl c. propargyl h. phenyl i 7. benzyl p 8. primary amine o q 9. secondary amine r 0. tertiary amine. quaternary ammonium ion l only the atom a only the atom b c d e f only the atom g h i r q p o n m l k j only the atom Do more than just exist.