Ochem1 – Chemistry – Flashcards
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Why do you think we put the distillate collection flask in an ice bath?
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because the alkene products are very volatile and the distillate collection flask will be in close proximity to the hot plate -- so the alkenes could evaporate if they are not kept cold
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In this experiment, you are to use 25 mL of a 1 M solution of potassium tert-butoxide. Calculate how many moles this is, and then answer this question: what is the limiting reagent in this experiment?
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2-bromo-2-methylbutane
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Why does the base used in this reaction, potassium t-butoxide, favor the E2 over the E1 mechanism?
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because it is a strong base, and strong bases favor second order reactions
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The name for this general type of reaction is
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dehydrohalogenation
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The mechanism of this reaction involves
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a transition state where the bromine and hydrogen are anti-periplanar
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The favored product in this reaction is
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the Hofmann product
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The difference between experiments 10.2A and 10.2B are the bases. The base in 10.2B is potassium tert-butoxide. The major difference between this base and the one used in 10.2 A is
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the size; i.e. the more sterically demanding organic base, t-butoxide, will favor abstraction of the more accessible proton
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In this experiment, the reaction mixture is refluxed for 1.5 hours and then the product is distilled. Because no materials are being removed from the reaction flask during reflux, it is okay to do the reflux part of the experiment without a magnetic stir bar.
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False
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This experiment calls for using 2.5 mL of 2-bromo-2-methylbutane. The molar mass and density of 2-bromo-2-methylbutane are 151.0 g/mol, and 1.18 g/mL, respectively. How many moles of 2-bromo-2-methylbutane are initially present? You must give your answer in decimal form, not scientific notation! And your answer must contain two significant figures, no more, no less. If your answer is a fraction, you must use a zero before the decimal point, e.g. 0.XX.
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0.020
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This experiment calls for using 25 mL of a 4 M solution of KOH in 1-propanol. How many moles of -OH will be initially present in this reaction? Your answer must contain two numbers and a decimal point -- one of the numbers can be (but does not have to be!) a zero, e.g. 50., or 5.0, or 0.5.
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0.1
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The substitution product of this reaction is
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unlikely because the alkyl halide is too sterically hindered
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In this experiment, the 2-bromo-2-methylbutane serves as the __________, and the potassium hydroxide serves at the __________.
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electrophile, nucleophile
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How is the product(s) isolated in this experiment?
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fractional distillation
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The major product in this reaction would also be known as
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the Zaitsev product
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While it is possible that more than one product will be formed in this reaction, the major organic product should be
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2-methyl-2-butene
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The product(s) in this reaction (experiment 10.2A) is/are formed by the _______ mechanism.
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E2/concerted
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In this experiment, the substrate molecule is 2-bromo-2-methylbutane which is a __________ alkyl halide, and the base is potassium hydroxide which is a ________ base.
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tertiary, strong
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Why is it proposed that the alcohol functional group is protonated by acid before dehydration can occur via EITHER an E1 or E2 mechanism?
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because -OH is a poor leaving group
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Why does the alcohol starting material have a higher boiling point than the alkene product(s)?
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two of these
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Please refer to Figure 10.10 on page 354 of the lab text. This Figure shows the gas chromatography (GLC) analysis of the product mix from the dehydration of 4-methyl-2-pentanol as done in this experiment. Note that there are four different product peaks! The Figure caption identifies what compound is responsible for each peak. The peaks and their respective compounds are listed below. Match the compounds with the mechanism that formed them. Peak 3, the major products, cis- and trans-4-methyl-2-pentene Peak 5, the major byproduct, 2-methyl-2-pentene Peak 2, 4-methyl-1-pentene Peak 4, 2-methyl-1-pentene
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E1, Zaitsev product E1 with hydride shift E1, Hofmann product E1 with two hydride shifts
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If the potassium carbonate were NOT removed from the liquid product prior to the final distillation, the potassium carbonate might relase its bound water molecules back into the liquid once the pot temperature reached 100 degrees. Then one of the purposes of the potassium carbonate would be defeated.
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Agree
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In this experiment, you added several spatula-tips full of anhydrous potassium carbonate to the liquid you had just distilled. The purpose of the potassium carbonate was to
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two of these
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The dehydration of 4-methyl-2-pentanol, and the dehydration of alcohols in general, is an example of an equilibrium reaction. In these kinds of reactions, we usually take certain steps to maximize the formation of the desired product. In the dehydration of 4-methyl-2-pentanol we encouraged the formation of the alkene product by
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removing the alkene product from the reaction vessel by fractional distillation
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The dehydration of 4-methyl-2-pentanol, and the dehydration of alcohols in general, is a reversible reaction.
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True
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Nucleophilic substitution is a general reaction for aliphatic compounds in which the leaving group is attached to an _______- hybridized carbon.
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sp3
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1-Bromobutane is an example of a __________ alkyl halide.
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primary
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In experiment 14.4, the formation of 1-bromobutane, what is the leaving group in the substitution reaction?
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water
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Since the formation of 1-bromobutane is an equilibrium reaction, we use the following technique to drive the reaction to the right:
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both A and B
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The reaction in this experiment is an equilibrium, as shown in equations (14.9) and (14.10) in the textbook. For the reverse reaction, i.e. the formation of 1-butanol from 1-bromobutane, what species would be the electrophile?
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CH3CH2CH2CH2Br
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The rate determining step in the formation of 1-bromobutane is
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attack of the nucleophile with simultaneous elimination of the leaving group
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By definition, nucleophiles are species that have at least one pair of nonbonding electrons and bear a negative charge.
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False
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In the preparation of 1-bromobutane, the electrophile is
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CH3CH2CH2CH2OH
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In the preparation of 1-bromobutane, the nucleophile in this reaction is
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Br-
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The preparation of 1-bromobutane in experiment 14.4 is an example of __________ reaction.
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an SN2
