2009%20203%20mt1-key - KEY student name/id_KEY c Consider...

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Unformatted text preview: KEY student name/id: ______________KEY________________________________ c) Consider the carbocations A-E below: CHEM 203 Midterm 1-Oct. 19, 2009 H CH3 surname given names H A last initial student number 2 3 B H H H C D E CH3 signature • the most stable carbocation of this set is: MOLECULAR MODELS MAY BE USED 1 H H 4 5 raw total E • the leas t s table c arboc ation of this set is: C total • rank (from least s table to mos t s table) the rem aining three ions in the set: 17 26 17 12 8 80 10 1. (17 marks) Answer each of the following parts. D B A least s table mos t stable a) Indicate whether each of the following compounds is aromatic (A), anti-aromatic (AA) or non-aromatic (NA) by circling the appropriate descriptor. CH2 O A AA NA A AA NA A AA A AA NA NA b) Circle all compounds whose 1H NMR spectrum is composed of two singlets: CH3 CH 3 CH3 C O CH3 O OEt O O Page 1 of 10 O nitrogen 1 N d) 1,8-Diazadibicyclo[5.4.0]undecene-7 (DBU) is a frequently used organic base. DBU: N nitrogen 2 • draw the product of the reaction between aqueous hydrochloric acid and nitrogen 1 of DBU: • draw the product of the reaction between aqueous hydrochloric acid and nitrogen 2 of DBU: H N Cl N N N N H Cl N H all of these none of these • using your answers above, which nitrogen atom reacts more readily with aqueous hydrochloric acid (circle your answer): Page 2 of 10 nitrogen 1 nitrogen 2 student name/id: ______________KEY________________________________ student name/id: ______________KEY________________________________ 2. (26 marks) Answer each of the following parts. d) The 1H NMR spectrum for compound X is given below. Circle the structure of X. a) Provide the hybridization of the indicated atoms: sp sp2 H N H H CCC H N H sp3 O sp3 b) Circle any compounds that are produced by the reaction between 1,3,3-trimethylcyclopentene and HBr. Br H3C CH3 Br H3 C Br CH3 CH3 H3C H3C CH3 Br Br CH3 CH3 H3C none are products CH3 c) Using pictures and brief comments, provide an rationale explaining why ethanol is a stronger acid relative to diethylamine (note: pictures=1000 words) OH OH stronge r acid vs, N H we ak er acid N H bas e base relative ratio under signals 2 2 3 CH3 O CH3 N CH3 In ethanol, the negative charge of the conjugate base that is formed on deprotonation is localized on an oxygen atom. CH3O OCH3 O CH3 O O CH3O O CH3 O compare s tability of conjugate bases 3 OCH3 CH3 O CH3 CH3 O e) Indicate whether each of the following molecular species is a Lewis acid (LA) or a Lewis base (LB) by circling the appropriate descriptor. In diethylamine, the negative charge of the conjugate base that is formed on deprotonation is localized on a nitrogen atom. CN Oxygen is more electronegative relative to nitrogen, and can better stabilize a negative charge. Page 3 of 10 LA LB CH3BH2 LA LB MgBr2 LA LB (CH3)2CH+ LA LB Page 4 of 10 student name/id: ______________KEY________________________________ student name/id: ______________KEY________________________________ f) Hydrocarbon 1 (C10H20) is optically active. Treatment of 1 with ozone (O3, solvent, -78 °C) followed by dimethylsulfide (DMS) generates two compounds 2 and 3. Spectroscopic data for compound 2 (C5H10O) is provided below. Compound 3 is an optically active aldehyde with R-configuration. Provide the structures of compounds 1-3. 3. (17 marks) Provide the requested information for each of the following reactions. If two stereoisomers are formed, draw both of them, clearly indicating appropriate stereochemistry. Do not draw the same stereoisomer twice. a) O O R H H R H CH3 H CHO R CH3 CH2 CH3 Br2, H2O (s olvent) H CH3 CH3 OH Br HO CH3 Br organic product(s) compound 1 (C10H20) compound 2 (C5H10O) IR: 1715 cm-1 NMR: ! 2.44 (q, ratio: 2) 1.06 (t, ratio: 3) compound 3 optically active aldehyde R-configuration b) a) Os O4, pyridine OH HO b) NaHSO3, H2O OH HO g) Of the two vitamins A and C shown below, one is water-soluble while the other is fatsoluble. Which is which? organic product(s) H3C CH3 CH3 CH3 water soluble c) OH CH3 Vitamin A (retinol) CH2OH O HO HO fat s oluble DH O OH water soluble OH D2, Pd/C solv ent HD OH DH HO HD fat s oluble Vitamin C (asc orbic acid) organic product(s) Page 5 of 10 Page 6 of 10 student name/id: ______________KEY________________________________ student name/id: ______________KEY________________________________ d) 4. (12 marks) Provide the products for the reactions below, and using arrows to represent electron movement, provide a detailed mechanistic rationale for each. a) H H3 O CH3 solv ent OH O CH3 O C C C H H2SO4 (c at.) CH3 HH CH3 H organic produc t(s) CH3 C C C HH H O H H C CH3 C C CH3 HH H H CH3 HH product H2 O (s olvent) H O H H O H H H O H CH3 O CH3 C H C CH3 HH H OH 1) protonation of the alkene 2) addition of water to a carbocation intermediate 3) removal of H+ to regenerate H3O+ catalyst e) O O NaO H OH solv ent O Na b) because of time constraints, ignore the B-R groups (use the cyclopentyl group)… a) NaOH, H2 O2 solvent organic product(s) B R x) a) BH3•THF CH3 CH3 b) NaOH, H2O 2 H H CH3 OH H (±) B R R product R b) NaOH, H2 O workup now to step b R BR O O O H O B R OH R R OH O OH H H O O H OH B RR O BR HO R 1) addition of peroxide ion to organoboron compound (Lewis acid-Lewis base rxn) 2) m igration of carbon from B to O step b 3) LA-LB reaction; reverse of LA-LB reaction; Bronsted acid-base reaction Page 7 of 10 Page 8 of 10 R OH CH3 organic starting m aterial(s) O B student name/id: ______________KEY________________________________ student name/id: ______________KEY________________________________ 5. (8 marks) The spectral data for unknown A (C5H9BrO2) is given below: This page should be used for ROUGH WORK only. Work on this page will NOT be graded. You can rip this page off if you want. IR: 1743 cm-1 1 H NMR: ! 3.91 (q, 2H) 3.70 (q, 1H) 1.63 (d, 3H) 1.17 (t, 3H) a) From your analysis of the spectral data above, what principal structural subunits are present? Draw these fragments in the space provided. • 1° unsaturation (double bond or ring) H CH3 C H CH3 C H O (for partial credit only; not required for full credit) b) Your final answer: HO H CH3 C C O C CH3 Br H End of questions Page 9 of 10 Page 10 of 10 ...
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This note was uploaded on 12/09/2009 for the course CHEM 203 taught by Professor Unknown during the Spring '98 term at UBC.

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