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Studocu is not sponsored or endorsed by any college or university Exam 01 key.pdf Organic Chemistry I (University of Minnesota, Twin Cities) Studocu is not sponsored or endorsed by any college or university Exam 01 key.pdf Organic Chemistry I (University of Minnesota, Twin Cities) Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

Problem 1 (10 points). Electronic structure. Answer the questions below as described. a ) Sulforphane (below) is a compound that is released when broccoli is chopped up. In the provided boxes, supply the answers about the atoms and bonds in its molecule: Hybridization of sulfur labeled as S1: Expected C-N-C angle in the molecule : Orbitals that make the C=N bond, from each atom’s side: Bond B1, σ-bond: C - N π-bond: C - N b ) Which of the following molecules will be the most polar (check box)? O 2 CO 2 CS 2 SO 2 c ) Which of the following compounds will have the highest boiling point (check box)? CF 4 NF 3 OF 2 LiF Problem 2 (6 points). Lewis structures. Answer the questions below as described. a ) In the following Lewis structure indicate what formal charges should be on each of the specified atoms. Write “0” for no charge, and “-1”, “-2”, … and “+1”, “+2”, ... for positive and negative charges Charge on O: Charge on N: Charge on C: b ) What should be the overall charge of this molecule? c ) How does the structure in a) relate to the structure below (check box)? isomer resonance form not an isomer or a resonance form N C O O C N B1 S O C N S Sulforaphane S1 sp 3 sp 3 120 sp sp 2 p p -1 +1 -1 -1 LP + 3 bonds N is sp 2 LP + 2 bonds C is sp, N is sp 2 O=O bond non-polar, in CO 2 and CS 2 polarities cancel out. In SO 2 they do not – it’s bent C O O C S S S O O LiF is ionic, so stronges IMF. NF 3 and OF 2 are polar (dipole-dipole), CF 4 is non-polar Different order of connection: OCN vs. OCN: isomer Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

Problem 3 (8 points). Resonance. Answer the questions below as described. a) Draw (as a Lewis structure , showing lone pairs and formal charges) a significantly contributing resonance structure for the following N N C C H H b) Draw (as a Lewis structure , showing lone pairs and formal charges) a significantly contributing resonance structure for the following O C C O H H H c ) How do the following resonance forms compare by relative contribution (check box) A > B > C A > C > B B > A > C B > C > A C > B > A C H H H O H N B C H H H O H N C A H H H O H C N Problem 4 (9 points). IUPAC nomenclature. Answer the questions below as described. a) Draw 2,3-dicyclopropylbutane b) Draw trans -1-ethyl-3- tert -butylcyclopentane c ) Write the IUPAC name for the following structure 3-ethyl-2-methylhexane or :A-B=C ↔A=B-C: pattern C N H H :A-B□ ↔A=B pattern C C H H H O Octets; + on N No octet on C Octets;+ on O Longest chain with most substituents highlighted Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

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Problem 5 (19 points). Acid-base reactions. Answer the questions below as described. a) Which is a stronger acid (check box) b) Which is a stronger base (check box) A B O H O H vs. A B A B O S vs. A B c) Which is a stronger acid (check box)? A B OH HO OH HO vs. A B d) Which is a stronger acid (check box), and briefly explain your choice Briefly explain your choice A B OH O OH O vs. A B e) Show the electron flow and draw the favored acid-base reaction between the following acid and base + O N H + OH N f) Show the electron flow and draw the favored acid-base reaction between the following acid and base + O H + O Conjugate base of B is stabilized by resonance, conjugate base of A is not Note: partial credit for inductive effect reasoning (it is less significant) H-O vs. HO ⊕ Conjugate base of HOR vs. HSR O is farther from OH, closer Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

Problem 6 (8 points): Lewis acid-base reactions. For the following Lewis acid-base reactions show electron flow , and draw the Lewis acid-base adduct resulting from their reaction: a ) Al Cl Cl Cl + С O H H С O H H Al Cl Cl Cl b ) H H H C + H H O H H H C O H H Problem 7 (10 points). Conformations around a single bond. For questions a-c consider the conformation A of 2-methylpentane over C2-C3 bond shown below, along with the energy diagram of its rotation around that bond. C 2 H 5 H H H H 3 C CH 3 A a) What point on the energy diagram corresponds to A (check box)? I or VI II or IV III V b) What is the dihedral angle between H and C 2 H 5 in conformation A? c) Draw (as a Newman projection ) the conformation that corresponds to point III on the diagram: C 2 H 5 H H H 3 C CH 3 H d ) What is the relative position of C 2 H 5 and H in the conformation shown in c) eclipsed gauche anti E dihedral angle I IV III II VI V 60 Staggered: must be a dip. Less repulsion that in another staggered: One of the lower dips The C-H and C-C 2 H 5 bonds forming the angle highlighted: gauche, 60 o III is a dip, must be a staggered conformation. A higher dip – so the staggered with greater repulsion than A: 2x CH 3 – C 2 H 5 gauche repulsions, A only has one. Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

Problem 8 (12 points). Chair conformations. Answer the questions below as described. a) Using the blank chair templates below, draw the two chair conformations of the following compound H 3 C H 3 C CH 3 CH 3 H 3 C CH 3 CH 3 CH 3 H 3 C b) Indicate which is going to be more stable (check box) the one on the left the one on the right both equal in stability c) Briefly explain your choice for b) Two CH 3 s are equatorial, one axial vs. two axial, one equatorial d) Which of the following is the most stable conformation of cis - 1-isopropyl-4-methylcyclohexane (check box) H 3 C CH 3 H 3 C H 3 C A B C D E A B C D E Will depend on the drawing above. For this one: on the right Note: Other versions of it are possible Less stabe: i-Pr axial Not a cis- Not a cis- Not 1,3 Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

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Problem 9 (6 points): Isomers. Answer the questions below as described. a) How would the following compounds relate to each other? (check box) vs. same constitutional isomers stereoisomers not isomers b) How would the following compounds relate to each other? (check box) H CH 3 C 2 H 5 C 2 H 5 H H vs. same constitutional isomers stereoisomers not isomers c) How would the following compounds relate to each other? (check box) vs. same constitutional isomers stereoisomers not isomers Problem 10 (12 points). Miscellaneous. Check the appropriate box for each question. a) How is the following reaction classified? Reduction Oxidation Not a redox reaction OH H H O H H H b) How is the following reaction classified? Reduction Oxidation Not a redox reaction H O Cl H H c) Which of the following alkanes will have the highest boiling point ? A B C D E A B C D E d) What type of strain is di-axial interaction? torsional strain angle strain ring strain steric strain (continued on the next page) C 5 , 1 ring C 5 , no rings Different composition Different composition C 2 H 5 C 2 H 5 H H H H 3 C C 7 C 6 C-H and C-O added C-H, 2x C-Os, C-Cl added B contains most Cs and no branches Di-axial interaction is a repulsion between substituents in two axial positions Repulsion between groups → steric repulsion → steric strain Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760

e) What is a correct electron flow for the following resonance? A B C D OH H H OH H H OH H H OH H H OH H H OH H H ... ... ... ... A B C D f) Which of the following bonds is expected to be the shortest ? C-H C-O C-C H-H The smaller the atoms, the shorter the bond. H is the smallest of atoms, so H-H bond will be the shortest Downloaded by Kyla Fung (always.kylafung@gmail.com) lOMoARcPSD|17650760