Orgo Lab Final Discussion set – Flashcards
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What is a bronsted lowry acid? what is a bl base?
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acid - proton donor base - proton acceptor (h ions)
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what happens when an acid is treated with base? and vice versa
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base steals H ion from acid - increases concentration of OH molecules - makes it more basic. pH raised acid donates H to base. increases H3O concentration - makes it more acidic. lowers pH
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How does an acid base rxn influence solubility of each component in soln to allow seperation?
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benzioc acid treated with OH base - makes a salt - soluble in water - now can seperate aqueous and organic layer
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why does a neutral compound fail to react when treated with acid/base in extraction
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triphenylmethane (neutral) never exits organic phase pka = 30 no affinity for basic or acidic media because weak acids/bases are already stable enough (note: reactivity favors weak acid/base formation)
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Why is it important to have dry glassware/atm for grignard rxn?
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because in the presence of water grignards will react with water and produce alkanes
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describe rxn to prepare methyl magnesium iodide. how many equivalents of memgi relative to benzoin? Why is this necessary?
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mg is oxidized and a polarized metal cation bond is formed complete when all mg turning consumed and mix is cloudy white 5 equiv necessary because acid base rxns are faster than electorphile nucleophile rxns so that will occur first so need more equivalents to ensure rxn carries out
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why do we need 10% h2so4 at end of grignard rxn?
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bc an alkoxide ion intermediate is formed when grignard reacts with ketone but the acid will transform it to a tertiary alcohol. ensures no excess magnesium in rxn. (quench)
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why two recrystallizations needed in grignard rxn?
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maximized purity of product helps to obtain more accurate melting point
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how do you use TLC to identify products obtained from dihydroxylation rxns? Can you get yield from TLC?
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comparison between cis, trans, and 50/50 known compounds regarding distance traveled. used anisaldehyde to stain. compared spots. No. qualitative, not quantitative.
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why use silver acetate in woodward dihydroxylation rather than sodium acetate?
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silver is bigger. holds its electrons less strong. more easily donated. faster attack.
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explain results of oxidation of 4-bromoethylbenzene. how do you test it? what will happen if another alkyl group attached to benzene?
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it oxidized to a carboxylic acid bc of kmno4. test - melting point compared to lit val. (could go farther and use NMR for exact structure) if another alkyl group attached - also oxideized to carboxylic acid.
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what if 4-methoxytoluene used instead of 4-cholortoluene?
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rxn would be faster because resonance stabilized bc of oxygen so transition more stable so faster rxn overall
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why destroy excess kmno4 at end of rxn?
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it would not precipitate out of soln so you wouldnt be able to filter it out when obtaining product
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what is purpose of celite pad? why rinse it with water after filtration of product?
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celite is used to capture suspended particles that would otherwise slip through regular filter paper. filter aid produces microscopic channels that let liquid through - not particles. water rinse needed so that anything that should have passed through actually does.
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what if you dont add enough acid HCl after the celite filtration?
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need excess H ions to form carboxylic acid
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discuss rxn of sodium iodide with hypochlorite
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produces iodine anion. is electrophilic and neutrophilic. turns reddish brown because of appearance of iodine. when it gets consumed, goes to yellow. all gone when soln light blue.
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why add sodium thiosulfate after rxn takes place?
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to act as base to extract H on ring to restore aromaticity.
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would you expect ionization of benzamide under same conditions to be faster/slower than salicylamide?
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benzamide will react slower due to superior stability. resonance stabilizes it. has deactivating group. salicylamide has activating and deactivating group. has tertiary carbocation intermediate - will react quicker.
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what is favored conformation of 1,3 butadiene
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trans (more thermodynamically stable)
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what conformation 1,3 butadiene needed for diels alder rxn?
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cis (although steric repulsion of H's) - required for dieonophile to attack the 1,4 positions simultaneously.
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if you use 2,5 dihydofuran instead of maleic acid, faster/slower/same?
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slower because absence of pi bonds to oxygen. these bonds are moderate deactivators. pull e density away from c-c bonds making them more positive and thus stronger dienophile.
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why add petroleum ether?
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to esnure product will dissolved in toluene. pet eth is nonpolar. will precipitate product out of toluene so it can be captured in filter.
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why aldol addition product favored at low temp and condensation favored at high temp?
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less investment E needed to produce addition product. Condensation product --> heat - base catalyzed elimination occurs - expels water - more thermodynamic product - conjugated/stable
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which product has higher melting point in aldol rxn? why?
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condensation has nonrotatable double bond harder to break. higher mp bc tighter packed conformation.
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advantages of using water as solvent in chem
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versatile solvent safe nontoxic green
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what role does steric hindrance play in oxidation of hydroxyl groups in oxidation race rxn?
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no role. only factor was formation of carbocation - how stable it was. secondary favored. primary impossible to form.
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what is reason for green yellow color in oxidation rxn?
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cl2 gas formed after functioning as a leaving group that originated the sodium hypochlorite
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why pour rxn into ice brine instead of plain ice?
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ice brine reduces solubility of product in water so that it can enter organic layer
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why wash ether layer with sodium carbonate followed by sodium hydroxide
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carbonate is weaker base and neutralizes with less violence that sodium hydroxide
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fischer esterfication: what drove the reaction forward?
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excess acid and heating rxn to reflux
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fischer esterfication: why extract the sodium carbonate soln?
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to react with excess acid, form salts and be removed through the aqueous layer.
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fischer esterfication: Why do you use a stir bar in the distillation pot instead of boiling chips:
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Since the distillation is under vaccuum boiling chips become ineffective. they need the presence of oxygen
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fischer esterfication: why isnt it necessary to have a thermometer:
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this distillation is under vaccuum therefore it must be a closed system and only open to the vaccuum. With the thermometer in place and under vaccuum we could risk breaking the thermometer and it would not be an effectively closed system. The other part of that question would be this distillation is simply being done to perform purification of a single product. We are not separating a mixture as we did last semester so we do not need to measure the bp. Also, since the reaction is under vaccuum the reduced pressure reduces the actual boiling point!
