CHE202A - Past Exam 2

CHE202A - Past Exam 2 - 1. Circle the correct answer: (50...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1. Circle the correct answer: (50 pts) (1) A simple allylic bromide can undergo: a. SN1 reaction more easily than SN2 reaction. b. SN2 reaction more easily than SN1 reaction. c. either SN1 or SN2 reaction depending on the reaction condition. d. neither SN1 nor SN2 reaction under any conditions. (2) How many intermediate(s) is (are) involved in a Diels-Alder reaction? a. 0 b. 1 c. 2 d. 3 e. 4 (3) Which provides the greatest stabilization to a conjugated diene? a. Delocalization of its π electrons. b. Hybridization of its carbons. c. Increased dipole moment. d. Coplanarity of all of its hydrogens. e. Polarization of its sigma electrons. (4) In the electrophilic addition of H-X to the π-bonded system of a conjugated diene, 1,2- and 1,4-addition often compete with each other because of: a. Resonance stabilization of the intermediate carbocation. b. Interconversions of bonding and antibonding molecular orbitals. c. Interconversions of sp2 and sp3 hybridized carbons. d. The presence of two or more bonding molecular orbitals in the π system. e. Interconversions of allylic and vinylic structures within the molecule. (5) Which of the following is an INCORRECT description of benzene? a. The CCC bond angles are equal to 120o. b. The molecule is planar. c. The molecule is a 6-membered ring which contains alternating single and double carbon-carbon bonds. d. The molecule is aromatic e. The molecule can be drawn as a resonance hybrid of two Kekule structures. (6) Aromatic molecules contain a. no d. 4n (n = integer) π electrons. c. 4n+2 (n = integer) b. 4n-2 (n = integer) e. unpaired (7) The -NH2 group activates the benzene ring toward electrophilic aromatic substitution. At which ring position(s) is this activation least effective? a. meta b. para c. ortho d. ortho and meta e. ortho and para (8) A resonance-stabilized carbocation structure forms as an intermediate when an aromatic ring undergoes electrophilic aromatic substitution. What chemical term refers specifically to this structure? a. sigma complex c. alkenium carbocation e. electrophilic state (9) What characteristic of the methoxy group causes it to direct electrophiles to the ortho and para positions of anisole? a. inductive stabilization b. removal of ring electrons through resonance c. interaction of the hydrogens of the methyl group d. donation of the oxygen's nonbonding electrons to the ring through resonance e. removal of ring electrons because of oxygen's electronegativity (10) What is the best method for converting benzene to n-propylbenzene? a. benzene, Cl-CH2-CH2-CH3, AlCl3 b. toluene, ethyl chloride, AlCl3 c. benzene, CH3-CH2-CO-Cl, AlCl3, then H2O; then Zn(Hg) and aq. HCl d. benzene, Cl-CO-CH3, AlCl3 toluene, Cl-CO-CH3 b. product precursor d. benzenoid adduct 2. Provide the structure(s) of all possible products in each of the reactions shown below. Show stereochemistry when appropriate. (20 pts) O (a) O + CH3CH2CCl AlCl3 (4 pts) (b) CH3 CH3 HNO3 H2SO4 (4 pts) SO3H SO3H Br (c) HBr 1,4-addition Br + (4 pts) O (d) + (4 pts) OCH3 OCH3 O CO2CH3 CO2CH3 or! CO2CH3 CO2CH3 (4 pts, -1 pt w/o showing cis relatioship) 3. What diene and denophile would react to give the product below? Is this the endo or exo product? (10 pts) H CO2CH3 CO2CH3 (4 pts) This is the endo product (2 pts). (4 pts) 4. Provide a detailed, stepwise mechanism for the reaction below. (20 pts) C(CH3)3 (CH3)2CHCH 2Cl AlCl3 (a) !+ !" (CH3)2C-CH2 H (b" Cl + AlCl3 (CH3)2C-CH2 H C(CH3)3 Cl AlCl3 (CH3)2C-CH3 + AlCl4 + (2 pts for TS) (2 pts) + (CH3)2C-CH3 H + Cl!AlCl3- C(CH3)3 + HCl + AlCl3 (4 pts) (2 pts each of the 6 arrows) 5. Provide the major resonance structures of the ion which results when the most acidic hydrogen of cyclopentadiene is removed as a proton. Is this ion aromatic? (10 pts) H H H -H+ H H H H 0.4 pt for each resonance structure w/ the nagative charge (and/or the lone pair); 0.4 pt for each curved arrow; This ion is arromatic (4 pts) 6. Please draw the major product of the following reaction. (10 pts) O CH3CH2CCl AlCl3 CH3CH2 ! C O O O C O C (5 pts if only the ortho acylated product is shown) 7. Please draw the structures of the two 1,2-addition (kinetic) products for the following reaction. Which one of the two products is the major one? Briefly explain you choice using words and diagram. (20) H3C HBr 1,2-addition Br Br and (4 pts) (4 pts) This is the major product (4 pts) The formation of the major product involves a tertiary (3o) allylic carbocation intermediate (3 pts, either words or showing the structure) 3o that is more stable (2 pts) than the secondary allylic carbocation intermediate (3 pts, either words or showing the structure) responsible for forming the minor product: 2o 8. Assuming a planar shape for the following species, indicate if they are: i) aromatic, ii) not aromatic, or iii) anti-aromatic. (10 pts) (a) O (b) CH2 B H aromatic (5 pts) B H non-aromatic (5 pts) 9. Extra credit. The triene shown below reacts with 2 equivalents of maleic anhydride via two successive [4+2] cycloaddition reactions. Please draw the structures of products A and B. (10 pts. 5 pts/each structure) O O [4+2] addition O + O O maleic anhydride A O B (C17H16O6) O O O O O O O O O A B ...
View Full Document

This note was uploaded on 10/10/2010 for the course CHE 202 taught by Professor Richard during the Spring '05 term at SUNY Buffalo.

Ask a homework question - tutors are online