o chem test 2 study – Flashcards
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What is the hybridization of the oxygen atom in dialkyl ethers?
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sp3
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Which of the following corresponds to the COC bond angle in dimethyl ether?
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110
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Which has the higher boiling point, diethyl ether or butan-1-ol? Briefly explain.
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Butan-1-ol has the higher boiling point since intermolecular hydrogen bonding can occur. Molecules of diethyl ether are incapable of hydrogen bonding with each other.
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Which
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They have relatively high boiling points for their molecular weights.
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Give two properties of ethers which allow them to be commonly used as solvents in organic reactions.
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Dissolve a wide variety of both polar and nonpolar compounds. 2. Tend to be unreactive under a large number of reaction conditions. 3. Have low boiling points; easily removed from product mixture.
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What complex results when BF3 is dissolved in dimethyl ether?
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(CH3)2O?BF3
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Anisole is known by two other names. Give either of them.
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Anisole is known by two other names. Give either of them.
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Provide a structural representation of isopropyl tert-butyl ether.
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(CH3)2CHOC(CH3)3
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What is the correct IUPAC name for the following compound?
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A) 3-methyl-3,4-epoxypentan-1-ol
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Which of the following is not a true statement?
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Oxetanes are five-membered ring ethers.
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What is the complete systematic IUPAC name for the following compound?
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D) (E)-4-isopropoxy-4,5-dimethylhex-2-ene
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Provide an acceptable name for the compound shown below. CH3OCH2CH(CH3)2
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isobutyl methyl ether or 1-methoxy-2-methylpropane
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In mass spectrometry, what is the most common fragmentation of ethers?
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Cleavage next to one of the carbon atoms bonded to oxygen
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Propose a structure for the ether of formula C4H10O with the following 1H NMR signals: ? 1.20 (triplet, 6H), ? 3.45 (quartet, 4H) (ppm).
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: CH3CH2OCH2CH3
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Propose a structure for the ether of formula C4H10O with the following 1H NMR signals: ? 0.95 (triplet, 3H), 1.52 (multiplet, 2H), 3.30 (singlet, 3H), 3.40 (triplet, 2H) (ppm).
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CH3CH2CH2OCH3
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Propose a structure for the ether of formula C4H10O with the following 1H NMR signals: ? 1.13 (doublet, 6H), 3.30 (singlet, 3H), 3.65 (septet, 1H) (ppm).
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(CH3)2CHOCH3
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What is the chemical shift of the carbon bound to oxygen in ethers in 13C NMR?
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: ? 65 to ? 90
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The Williamson ether synthesis occurs by the ________ mechanistic pathway.
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SN2
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39) Which pair of reagents would produce the highest yield of (R)-2-ethoxybutane?
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sodium (R)-2-butoxide + iodoethane
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40) Which of the following is an acceptable way to synthesize t-butyl ethyl ether?
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heating a mixture of ethanol and t-butanol in sulfuric acid
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Show the reagents necessary to prepare 1-ethoxy-1-methylcyclopentane from 1-methylcyclopentene.
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Hg(OAc)2, CH3CH2OH 2. NaBH4
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When cyclohexene is subjected to mercuration in methanol and the resulting mixture is reduced with sodium borohydride, the major organic product is:
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methoxycyclohexane.
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When pent-1-ene is treated with mercury(II) acetate in methanol and the resulting product is reacted with NaBH4, what is the primary organic compound which results?
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) 2-methoxypentane
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Show the reagents necessary for the conversion of 1-bromo-1-methylcyclopentane to 1-ethoxy-1-methylcyclopentane.
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CH3CH2OH, heat
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Provide two reasons why it would be difficult to prepare ethoxycyclopentane via an intermolecular dehydration route from ethanol and cyclopentanol.
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1. Secondary alcohols tend to yield alkenes under these conditions. 2. Symmetrical ethers would be produced as well.
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Can one prepare di-sec-butyl ether in good yield by heating butan-2-ol in the presence of sulfuric acid? Explain.
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This would not be an appropriate method of preparing di-sec-butyl ether in good yield. When butan-2-ol, a 2° alcohol, is heated in the presence of strong acid, the major product is 2-butene, the elimination product.
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When hexan-1-ol is treated with conc. H2SO4 at moderate temperatures, ________ is formed via a(n) ________ mechanism.
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) di-n-hexyl ether, SN2
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Some ethers can be prepared by heating the appropriate alcohol in the presence of sulfuric acid. Can di-sec-butyl ether be prepared from sec-butanol by this route? Explain your answer.
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No. sec-Butanol is a secondary alcohol. Secondary and tertiary alcohols predominantly undergo elimination when heated in acid.
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67) What are the expected products of the reaction of PhOCH3 with concentrated HI?
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B) phenol and iodomethane
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69) Di-n-pentyl ether can be converted to 1-bromopentane by treatment with HBr through essentially a(n) ________ mechanism.
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A) SN2
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70) Treatment of tetrahydrofuran with excess HBr results in the formation of what major organic product?
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C) 1,4-dibromobutane
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What is the major organic product which results when tetrahydrofuran is reacted with excess HBr?
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1,4-dibromobutane
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The presence of what product of the autooxidation of ethers makes the distillation of ethers dangerous?
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dialkyl peroxides
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When ethers are stored in the presence of oxygen, what explosive materials can result from autoxidation of the ether?
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hydroperoxides or dialkylperoxides
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Which of the following compounds would undergo autoxidation most readily?
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A) dibenzyl ether
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81) What term is given to the sulfur analogues of ethers?
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sulfides or thioethers
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86) Which of the following is produced by the reaction of (CH3CH2)2S with CH3CH2I?
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B) (CH3CH2)3S+ I-
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87) In biological systems, sulfonium salts such as SAM serve what function?
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C) alkylating agents
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90) Provide the structure of the sulfonium salt that results when (CH3CH2)2S reacts with CH3CH2Cl. Through what mechanistic path is this reaction occurring?
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(CH3CH2)3S+ Cl-; SN2
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Why are sulfonium salts good alkylating agents?
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Sulfonium salts are good alkylating agents because the leaving group is an uncharged sulfide.
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) Show the reagents necessary to prepare trans-1,2-cyclopentanediol from cyclopentene.
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PhCO3H 2. H3O+
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95) When trans-hex-3-ene is treated with PhCO3H, the major organic product is:
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a 1:1 mixture of enantiomeric epoxides.
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96) Magnesium monoperoxyphthalate is often used as a reagent in what process?
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D) epoxidation
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Show the reagents necessary to prepare 1,2-epoxy-1-methylcyclopentane from cyclopentanone.
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. CH3MgBr 2. conc. H2SO4 3. PhCO3H
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Identify all of the following reagents that could be used to accomplish the following transformation.
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A) mCPBA B) DMD D) 1) Br2 / H2O, 2) NaH
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102) Through what mechanism can a 1,2-halohydrin be converted into an epoxide?
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B) SN2
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107) What results when but-1-ene is subjected to the following reaction sequence: (1) Cl2, H2O, (2) NaOH, (3) H3O+?
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D) a 1:1 mixture of enantiomeric diols
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109) What results when cyclopentene oxide is treated with aqueous base?
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A) a racemic mixture of trans-1,2-diols
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Show the reagents necessary to prepare trans-2-deuteriocyclohexan-1-ol from cyclohexene.
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PhCO3H 2. LiAlD4
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What is the major difference in the structure of the product formed in a Grignard reaction when an alkyl magnesium halide (Grignard reagent) is reacted with an epoxide rather than an aldehyde or ketone followed by work-up with H3O+?
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The alkyl group from the Grignard reagent will be bonded to the ?-carbon of the alcohol product.
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Show the reagents necessary to prepare 2-phenylethanol from bromobenzene
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Mg, ether 2. oxirane 3. H3O+
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What compound is formed when ethylene oxide is reacted with n-pentyllithium followed by treatment with aqueous acid?
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1-heptanol
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What compound is formed when methyloxirane is reacted with ethylmagnesium bromide followed by treatment with aqueous acid?
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A) 1-pentanol B) 2-pentanol
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125) What compound is formed when 2,2-dimethyloxirane is treated with ethanol containing a trace of HCl?
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A) 2-ethoxy-2-methyl-1-propanol
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Which of the following is an incorrect description of benzene?
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The molecule is a 6-membered ring which contains alternating single and double carbon-carbon bonds.
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Cyclic hydrocarbons which can be represented as structures containing alternating single and double bonds are called ________.
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annulenes
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What is the bond order of the carbon-carbon bonds in benzene?
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1.5
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When cyclohexene is treated with KMnO4, H2O, the syn-1,2-diol is produced. What reaction occurs when benzene is similarly treated?
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No reaction takes place.
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Why does benzene undergo a substitution reaction with Br2 while cyclohexene undergoes an addition reaction.
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Addition of Br2 to benzene is highly unfavorable because it would result in a nonaromatic product (aromatic stabilization would be lost).
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What is suggested by the fact that benzene's molar heat of hydrogenation is 36 kcal less than three times the molar heat of hydrogenation of cyclohexene?
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This suggests that the type of ? bonding in benzene lends special stability to the molecule.
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In the molecular orbital representation of benzene, how many ? molecular orbitals are present?
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6
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Which of the following undergoes SN2 reaction with sodium methoxide most rapidly?
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A) PhCH2Br
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9) Which of the following undergoes solvolysis in methanol most rapidly?
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B) Ph3CBr
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How many distinct nodal planes which are perpendicular to the molecular plane are present in the ?4* orbital of benzene?
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2
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How many pairs of degenerate ? molecular orbitals are found in benzene?
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2
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Show how the participating p orbitals interact to form the highest energy ? molecular orbital of benzene.
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All adjacent interactions are antibonding.
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) Describe the occupied p molecular orbitals in the ground state of cyclobutadiene.
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Two electrons are paired in a bonding p molecular orbital, while the other two electrons are unpaired and singly occupy two nonbonding p molecular orbitals.
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16) What is the major difference between an antiaromatic and aromatic compound?
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Only aromatic compounds follow Huckle's rule.
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22) Aromatic molecules contain ________ ? electrons.
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C) 4n + 2 (with n an integer)
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23) Which of the following is another name for cyclobutadiene?
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B) [4]annulene
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Classify 1,3,5-heptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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nonaromatic
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List the criteria which compounds must meet in order to be considered aromatic.
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The structure must be cyclic. 2. Each atom in the ring must have an unhybridized p orbital. 3. The structure must be planar or nearly planar so that overlap of these p orbitals is effective. 4. The ? network must contain 4n + 2 electrons (where n is a whole number), so that delocalization of the ? electrons results in a lowering of the molecule's electronic energy.
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Which is more stable, cyclobutadiene or 1,3-butadiene? Explain.
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1,3-Butadiene is more stable. Cyclobutadiene is antiaromatic since it contains 4 (i.e., 4n) ? electrons. Antiaromatic systems are less stable than their open-chain counterparts. Diff: 2
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) Is cyclooctatetraene a planar molecule? Explain.
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No. In addition to increasing other forms of strain, a planar conformation would make this molecule antiaromatic.
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) Classify cycloheptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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nonaromatic
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Classify cyclopentadiene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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nonaromatic
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Is the all-cis form of [10]annulene aromatic? Explain.
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No. Planarity, which is required for aromaticity, is precluded due to excessive angle strain.
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Is the [10]annulene shown below aromatic? Explain.
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No. The ring cannot achieve a planar conformation since such a conformation would result in severe and unfavorable steric interactions between the two H's oriented inside the ring.
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35) Which of the following is the same as the tropylium ion?
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A) cycloheptatrienyl cation
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Explain the relative acidities of cyclohexene (pKa of 46) and cyclopentadiene (pKa of 16).
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The conjugate base of cyclopentadiene is aromatic.
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Why would the reaction below proceed at an extremely slow rate if at all?
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The carbocation intermediate involved in this reaction is antiaromatic. Based on Hammond's Postulate, one can surmise that the activation energy required to produce this intermediate would be very high.
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When cycloheptatriene is deprotonated, an anion with seven resonance forms of equal energy can be drawn. Given this fact, explain why cycloheptatriene is only slightly more acidic than propene.
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Each resonance form of the cyclopehtatrienyl anion is antiaromatic.
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) 3-Chlorocyclopropene is solvolyzed in methanol at a much higher rate than is chlorocyclopropane. Offer an explanation.
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Cyclopropenyl cation, the carbocationic intermediate in the case of 3-chlorocycloprene, is aromatic and via Hammond's Postulate we can say that the activation energy required to form it is lower. Diff: 2
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Classify cyclopentadienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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antiaromatic
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Classify cyclopropenyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network
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aromatic
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Classify cycloheptatrienyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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aromatic
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51) Which sequence ranks the indicated protons in order of increasing acidity?
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D) 3 < 2 < 1
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What compound results when cyclooctatetraene is treated with excess potassium metal?
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dipotassium cyclooctatetraene dianion
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Which sequence ranks the indicated protons in order of increasing acidity?
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D) 3 < 2 < 1
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Which sequence correctly ranks the following substrates in order of increasing reactivity in an SN1 reaction?
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1 < 3 < 2
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56) Rank the following in order of increasing pKa (from lowest to highest pKa)
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C) 2 < 1 < 3
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Nitrogen's lone pair electrons occupy what type of orbital in pyridine?
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C) sp2
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Classify pyrrole as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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aromatic
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) ________ is similar to furan, with a sulfur atom in place of the oxygen.
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Thiophene
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Classify pyridine as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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aromatic
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Which is more basic, pyridine or pyrrole? Explain.
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Pyrrole is a much weaker base than pyridine. When pyrrole is protonated, the system's aromaticity is destroyed
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Which sequence correctly ranks the following dienes in order of increasing reactivity in the D-A reaction?
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A) 1 < 2 < 3
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73) Classify naphthalene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the ? network.
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aromatic
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76) Why are researchers interested in the properties of large polynuclear aromatic hydrocarbons?
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These compounds are formed to some extent in nearly all combustion reactions of organic compounds and are known to be potent carcinogens.
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78) Name two of the three common allotropes of carbon.
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diamond; graphite; fullerenes (like buckminsterfullerene)
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79) Which of the following is not a fused-ring heterocycle?
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B) pyrimidine
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86) How many distinct trichlorobenzene isomers are possible?
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B) 3
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87) Which of the following is another accepted name for methyl phenyl ketone?
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C) acetophenone
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88) Which of the following is also an acceptable name for 3-nitrophenol?
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B) m-nitrophenol
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92) Which of the following is also an acceptable name for 1,3,5-trimethylbenzene?
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B) mesityleneB) mesitylene
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Provide an acceptable name for PhSO3H.
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benzenesulfonic acid
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113) Which of the following compounds has the lowest boiling point?
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C) p-dichlorobenzene
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114) Which of the following compound has the highest melting point?
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E) p-dichlorobenzene
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In the UV-visible spectra of the following compounds, in which does lambda max appear at the highest wavelength?
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1-phenylpropene
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) In the proton NMR, in what region of the spectrum does one typically observe hydrogens bound to the aromatic ring?
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D) 7.0-8.0 ppm
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117) In the carbon NMR, in what region of the spectrum does one typically observe carbons which are part of the aromatic ring?
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D) 120-150 ppm
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118) Which of the following compounds has the most signals in the proton-decoupled 13C NMR spectrum?
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B) m-dibromobenzene
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19) In the mass spectrum of isobutylbenzene, the base peak occurs at m/z ________.
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91
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120) How many peaks are in the proton spin decoupled 13C NMR spectrum of p-dichlorobenzene?
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2
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122) How many peaks are in the proton spin decoupled 13C NMR spectrum of 1,2,3-trichlorobenzene?
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4
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The IR spectrum of m-xylene contains stretches which are characteristic of most aromatic hydrocarbons. List the peaks (in cm-1) associated with the aromatic CC stretch and the aromatic CH stretch.
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CC: around 1600 cm-1 CH: just above 3000 cm-1 (usually around 3030 cm-1)
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How might one distinguish the isomers of trimethylbenzene by noise-decoupled 13C NMR?
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1,3,5-trimethylbenzene: 3 signals 1,2,4-trimethylbenzene: 9 signals 1,2,3-trimethylbenzene: 6 signals
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Describe the benzenoid band which appears in the UV-visible spectrum of most aromatic hydrocarbons.
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Band centered at 254 nm; 3-6 small, sharp peaks; weak molar absorptivity.
