ochem ch9 – Chemistry – Flashcards
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How many distinct alkynes exist with a molecular formula of C4H6?
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2
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Give the IUPAC name for HC-=CCH2CH2CH3.
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pent-1- yne
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Draw an acceptable structure for acetylene.
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H-C-=C-H
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Give the IUPAC name for Cl3CCH2CH2CH2C≡CH.
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6,6,6-trichlorohex- 1-yne
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Provide the IUPAC name for Cl3C(CH2)3C≡CH.
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6,6,6-trichloro- 1-hexyne or 6,6,6-trichlorohex- 1-yne
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Provide the IUPAC name for (CH3)2CHCH2CH(OH)CH2C≡CCH3.
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2-methyl- 6-octyn- 4-ol or 2-methyloct- 6-yn- 4-ol
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Draw an acceptable structure for hepta-3,6- dien-1-yne
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HC-=CCH=CHCH2CH=CH2
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Give the IUPAC name for CH3CH=CHCH=CHC-=CCH3.
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octa-2,4- dien-6- yne
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Which of the following improperly describes the physical properties of an alkyne?
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insoluble in most organic solvents
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Which of the following alkynes has the lowest boiling point?
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3,3-dimethyl- 1-butyne
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The pi bond of an alkyne is ________ and ________ than the pi bond of an alkene.
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shorter, weaker
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How many moles of oxygen are required in the complete combustion of 1 mole of acetylene?
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2.5
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What products result when calcium carbide is combined with water?
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acetylene and calcium hydroxide
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How many moles of water are produced when one mole of propyne undergoes complete combustion?
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2
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The carbon-carbon triple bond of an alkyne is composed of ________.
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one σ bond and two π bonds
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In trans-hept- 4-en- 2-yne the shortest carbon-carbon bond is between carbons ________.
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2 and 3
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Which of the species below is less basic than acetylide?
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CH3ONa
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Among the compounds water, but-1- yne, but-2- yne, and ethane, which are stronger acids than ammonia?
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water and but-1- yne
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To a solution of propyne in diethyl ether, one molar equivalent of CH3Li was added and the resulting mixture was stirred for 0.5 hour. After this time, an excess of D2O was added. Describe the major organic product(s) of this reaction.
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CH3C-=CD + CH4
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What is the pKa of a terminal alkyne?
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25
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Why are terminal alkynes more acidic then other hydrocarbons?
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The carbanion which results upon deprotonation of a terminal alkyne has the lone pair of electrons in an sp hybrid orbital. The greater % s character of this orbital gives this orbital a significantly lower energy.
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Which of the following bases will favorably deprotonate a terminal alkyne? (More than one answer is possible.)
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A) n-BuLi B) LDA D) PhMgBr (Ph=phenyl)
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Describe a qualitative, nonspectroscopic means for distinguishing terminal alkynes from internal ones.
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Add a solution of Cu+ or Ag+. Terminal alkynes react to form insoluble metal acetylides which precipitate
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Which of the following bases are sufficiently strong to deprotonate a terminal alkyne with an equilibrium constant greater than 1?
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2) lithium diisopropyl amide 3) n-butyl lithium 4) phenylmagnesium bromide
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Describe a sequence of reactions by which hept-3- yne can be straightforwardly prepared from acetylene.
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1. NaNH2 2. CH3CH2Br 3. NaNH2 4. CH3CH2CH2Br
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Describe a sequence of reactions by which butylbenzene can be straightforwardly prepared from phenylacetylene.
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1. NaNH2 2. CH3CH2Br 3. H2, Pt
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2-Methylhex- 3-yne can be prepared by the reaction of an alkynide with an alkyl halide. Does the better synthesis involve alkynide attack on bromoethane or on 2-bromopropane? Explain your reasoning.
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Attack on the primary bromide (bromoethane) is much more favorable. Reaction of an alkynide with the secondary bromide would result mostly in elimination instead of substitution.
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Describe a sequence of reactions by which 1-propylcyclohexan- 1-ol can be straightforwardly prepared from propyne.
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1. NaNH2 2. cyclohexanone 3. H+, H2O 4. H2, Pt
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Why is a terminal alkyne favored when sodium amide (NaNH2) is used in an elimination reaction with 2,3-dichlorohexane?
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The strong base deprotonates the terminal alkyne and removes it from the equilibrium.
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When 2,2-dibromobutane is heated at 200°C in the presence of molten KOH, what is the major organic product?
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but-2- yne
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Describe a sequence of reactions by which hept-1- yne can be straightforwardly prepared from hept-1-ene.
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1. Br2 2. NaNH2, heat
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Treatment of hex-2- yne with mercuric sulfate in dilute sulfuric acid yields a mixture of two ketones. Similar treatment of hex-3- yne produces a single ketone instead of a mixture. Explain.
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The two carbons of the triple bond in hex-3- yne are equivalent, and only 3-hexanone results. In the case of hex-2- yne, the two carbons of the triple bond are not equivalent, and a mixture of 2- and 3-hexanone results.
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Which of the following describes an unsymmetrical addition reaction?
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propyne with 1 mole HBr
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Name the compound which results when pent-2- yne is subjected to catalytic hydrogenation using a platinum catalyst.
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pentane
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Describe a sequence of reactions by which trans-pent- 2-ene can be straightforwardly prepared from propyne.
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1. NaNH2 2. CH3CH2Br 3. Na, NH3
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Which of the following reagents should be used to convert hex-3- yne to (E)-hex- 3-ene?
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Na, NH3
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Which of the following reagents should be used to convert hex-3- yne to (Z)-hex- 3-ene?
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H2, Lindlar's catalyst
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A mixture of hept-1- yne, hept-2- yne, and hept-3- yne was hydrogenated in the presence of a platinum catalyst until hydrogen uptake ceased. If one assumes that the hydrogenation went to completion, how many different seven-carbon hydrocarbons were produced?
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1
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________ is produced when 1 equivalent of HBr is added to hex-1- yne in the presence of peroxides.
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A mixture of E and Z isomers of 1-bromohex- 1-ene
