Chem 109A In‐Class Exam 3 Sample Wed., Feb 26, 2010 Name: ________________________ Perm number: _________________ Name: ____________________________________ Perm number: __________________
Question 1) (46 pts) 2) (9 pts) 3) (15 pts) 4) (12 pts 5) (18 pts) Total (100 pts) Your score
1. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question (50 pts). . 1) The carbon-carbon triple bond of an alkyne is composed of __________. 1) _______ A) three π bonds B) three σ bonds C) one σ bond and two π D) two σ bonds and one π bonds bond 2) The reagent needed to convert 2-butyne to trans-2-butene is: 2) _______ A) H
2/Pt B) H
2/Lindlarʹs catalyst C) Li/NH
3 D) Na/NH
3 E) C or D 3) What is the IUPAC name for the following compound? 3) _______ A) 2Z,4Z-2, 4-heptadiene B) trans, trans-2, 4-heptadiene C) 2E,4E-2, 4-heptadiene D) cis, cis-2, 4-heptadiene E) cis, trans-2, 4-heptadiene 4) Which of the following is the best synthesis of 2, 2-dibromopropane A) 4) _______ B) C) CH3CCH D) E) 5) A mixture of 1-heptyne, 2-heptyne, and 3-heptyne was hydrogenated in the presence of a platinum catalyst until hydrogen uptake ceased. If one assumes that the hydrogenation went to completion, how many distinct seven-carbon hydrocarbons were produced? A) 1 B) 3 C) 2 D) 8 E) 6 6) __________ is produced when 1 equivalent of HBr is added to 1-hexyne in the presence of peroxides. A) 2-bromo-1-hexene B) a mixture of E and Z isomers of 1-bromo-1-hexene C) E-1-bromo-1-hexene D) E-2-bromo-2-hexene E) Z-1-bromo-1-hexene 7) Which of the following statements is not true about propyne, HCCCH3? 5) _______ 6) _______ 7) _______ A) The HCH bond angle is about 109.5°. B) The CCC bond angle is 180°. C) The pi bond is weaker than the sigma bond. D) It contains six sigma bonds. E) It contains three pi bonds. 8) How many distinct internal alkynes exist with a molecular formula of C6H10? A) 1 B) 2 C) 3 D) 4 E) 5 9) Which of the following statements correctly describes the general reactivity of alkynes? A) The σ bonds of alkynes are higher in energy than the π bonds and are thus more reactive. B) An alkyne is an electron-rich molecule and therefore reacts as a nucleophile. C) Unlike alkenes, alkynes fail to undergo electrophilic addition reactions. D) Alkynes are generally more reactive than alkenes. E) Alkynes reacts as electrophiles, whereas alkenes reacts as nucleophiles. 10) How many distinct terminal alkynes exist with a molecular formula of C5H8? A) 1 B) 2 C) 3 D) 4 E) 5 8) _______ 9) _______ 10) ______ 11) What are the products of the following reaction, CH3OH + CH3CC-Na+ → ? 11) ______ A) CH
3CCCH3 + NaOH B) CH
3OCCH + NaCH3 C) CH
3CCH + CH3O-Na+
D) CH
3CCOCH3 + NaOH E) no reaction 12) Which of the species below is less basic than acetylide? A) CH
3Li 12) ______ B) NaOH C) CH
3ONa D) both B and C E) all of the above 13) Which is the correct order of decreasing acidity in the following compounds? H2O CH3CH3 NH3 CH2CH2 HCCH A B C D A) A > E > D > B > C B) A > E > C > D > B C) A > C > E > D > B D) E > A > C > B > D E) E > D > B > A > C 14) What is the common name for the following alkyne? A) neohexyne B) trimethylacetylene C) trimethylpropyne D) isopropylacetylene E) tert-butylacetylene 13) ______ E 14) ______ 15) ______ 15) What is the kinetic product for the following reaction? A) I B) II C) III D) IV 16) What is/are the product(s) from the following reaction? E) V 16) ______ A) I only B) II only C) III only D) I and II E) II and III 17) What is the thermodynamic product for the following reaction? A) I B) II C) III D) IV E) V 17) ______ 18) What is the hybridization of the central carbon of allene (1,2-propadiene)? A) sp
2 18) ______ B) p C) sp
3 D) sp E) none of the above 19) What is/are the product(s) from the following reaction? 19) ______ A) I only B) II only C) I is minor, II is major D) equal amounts of I and II E) I is major, II is minor 20) Which of the following is the most stable diene? 20) ______ A) I B) II C) III D) IV 21) What is/are the product(s) from the following reaction? A) I and IV E) V 21) ______ B) I and II C) II and III D) II and IV E) I and III 22) Which of the following conjugated dienes would not react with a dieneophile in a Diels-Alder reaction? 22) ______ A) I B) II C) III D) IV E) I and III 23) Which of the alkyne addition reactions below involves an enol intermediate? A) treatment with HgSO
4 in dilute H2SO4 23) ______ B) hydroboration/oxidation C) hydrogenation D) both A and B E) both A and C 24) What type of organic product results when 1-butyne is treated with 6M aqueous NaOH? A) an enol B) an alcohol C) an aldehyde D) a sodium acetylide E) Not much reaction; most of the alkyne remains unchanged. 25) Which of the following improperly describes the physical properties of an alkyne? A) relatively nonpolar B) nearly insoluble in water C) insoluble in most organic solvents D) less dense than water
24) ______ 25) ______ Answer Key: 1) C 2) E 3) E 4) C 5) A 6) B 7) E 8) C 9) B 10) B 11) C 12) D 13) B 14) E 15) E 16) C 17) D 18) D 19) E 20) C 21) B 22) E 23) D 24) E 25) C 2. Strutures and Nomenclature (12 pts) 1) Draw a structure for each of the following names a) propargyl bromide b) methylacetylene c) allyl bromide d) benzene 2) Name the following compounds b)
OH
a)
a)
b)
Br
3) Indicate how each of the following compounds can be made from an alkyne. Give the structure of the best alkene to use and write the required reagents over and/or under each arrow (15 pts). 1) 2) 3) 4) 5) 4. SHORT ANSWER (18 pts). Write the word or phrase that best completes each statement or answers the question 1) Please list out the four rules for drawing resonance structures 2) Penta‐1,3‐diene is about 6 kcal/mol stable than penta‐1,4,‐diene. Answer the following questions (6 pts): a) Please draw the structures of each of the compounds. b) Draw all the resonance structures of each of the structures c) Explain clearly why the former is more stable than the latter using resonance theory d) Alternatively the stability of penta‐1,3‐diene can be explained using molecular orbital theory. i) draw all the Pi molecular orbitals of both dienes and indicating their relative stability ii) explain why penta‐1‐,3‐diene is more stable using those molecular orbitals. 3) Please explain why acetic acid is more acidic than ethanol using resonance theory 4) For the following reaction, which product is the kinetic product and which one thermodynamic? Use electron‐pushing arrows to outline the reaction mechanism. Under the indicated reaction conditions, which one is the major product? Why? 5) For the following Diels‐Alder reaction, please give the expected product indicating the stereochemistry. Also, please point out which one in the reactants is diene and which one is dienophile. 5. Please provide a reasonable synthetic sequence to achieve the preparation of the desired product using the designated starting material. You can use any reagent and solvent (9 pts).