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114 Cards in this Set
- Front
- Back
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characteristic functional group in a carboxylic acid
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carboxy group
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characteristic functional group in a sulfonic acid
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sulfonic acid group
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A carboxylic acid is named by adding the suffix
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ic and the word acid to the prefix for the appropriate group
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dicarboxylic acids
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carboxylic acids w 2 carboxy groups
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Successive dicarboxylic acids "(oh my such good apple pie)"
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oxalic, malonic, succinic, glutaric, adipic, pimelic
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phthalic acid
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aromatic dicarboxylic acid
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a carboxylic acid is named by dropping
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final e from hydrocarbon w same number C atoms & adding suffix oic acid
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Is the final e dropped in naming dicarboxylic acids?
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No
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Name this compound
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octanedioic acid
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When a carboxylic acid is derived from a cyclic hydrocarbon, the suffix
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carboxylic acid are added to name of hydrocarbon
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The principal chain in substituted carboxylic acids is numbered by assigning the number 1 to
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the carbonyl carbon
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In carboxylic acids derived from cyclic hydrocarbons, numbering begins @
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the ring carbon bearing the carboxy group
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Priority for citation as principal group
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HO2C-CH2 substituent
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carboxymethyl group
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Carboxylic acid geometry
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trigonal
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C-O (Carboxylate oxygen) bond is ___ than the C-O bond in an alcohol or ether: why?
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shorter (In an acid it is sp2-sp3 hybridized, in alcohol or ether sp3-sp3 single bond)
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The carboxylic acids of lower mlclr mass are
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high boiling liquids w acrid, piercing odors & higher bp than other organic cmpds of same mlclr mass & shape
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Why do carboxylic acids have high bp?
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polarity & strong hydrogen bonds formed
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In solid state & sometimes in both gas phase & solution, carboxylic acids exist as
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H-bonded dimers w large equilibrium constants
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Many aromatic & dicarboxlyic acids are
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solids
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Simpler carboxylic acids are
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soluble in h2o as expected from H-bonding capabilities (unbranched carb acids below pentanoic acid are miscible w h2o)
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C=O stretching absorption
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1710 cm-1 (benzoic acid: 1680)
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carb acid OH stretch absorption
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broader than OH in alcohol or phenol, covers 2400-3600
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a-protons of carb acids NMR absorption
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2-2.5 ppm
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OH proton resonance
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9-13 ppm region, often broad
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How to distinguish acid proton from aldehydic proton?
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acid proton like alcohol rapidly exchanges w D2O
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diff btwn carb acid & aldehyde/ketone 13C NMR & why
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carbonyl carbon of acid has somewhat smaller chem shift than aldehyde/ketone bc of shielding effects of unshared e pairs on carboxylate O
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Why are carb acids acidic?
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Ionization of the OH group
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carboxylate ions
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conjugate bases of carboxylic acids: replace ic with ate
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What is most acidic, alcohol, phenol or CA?
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ROH < Ph-OH < CA
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Why is CA so acidic?
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polar effect of carbonyl gorup (sp2 hybridized atoms, so partial pos charge on carbonyl C, presence of O more electroneg than phenyl or alkyl) stabilizes charge in carboxylate ion = enhanced acidity + resonance stabilization of carboxylate ion
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halogen substitution within the alkyl group of a carboxylic acid ___ acidity by __
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enhances - polar effect
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Sulfonic acids are much ___ than comparably substituted carboxylic acids
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stronger
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Why is sulfonic acid so acidic?
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Sulfur's high oxidation state: octet structure indicates positive charge on sulfur: stabilizes neg charge on oxygens
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Sulfonic acids are __ soluble than most inorganic acids
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more
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Sulfuric acid is ___ soluble in benzene and toluene
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insoluble
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Many carboxylic acids of moderate mm are ___ in water while alkali metal salts are ___
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insoluble -- more soluble
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Many water-insoluble carboxylic acids dissolve in solutions of alkali metal hydroxides NaOH, KOH because
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the insoluble acids are converted completely into their soluble salts
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Henderson-Hasselbach equation
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A typical CA can be separated from mixtures with other
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water-insoluble, nonacidic substances by extraction w NaOH, Na2CO3, or NaHCO3
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After separating the basic aq. solution, it can be acidified w a strong acid to yield CA, which may be
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isolated by filtration or extraction w organic solvents
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CA can also be separated by extraction w 5% NaHCO3 if the phenol is not unusually
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acidic
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Why does the phenol remain largely unionized and thus insoluble in an aq. solution w a pH of 8.5?
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the pka of a typical phenol is about 10
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The carbonyl oxygens of acids like ald/ket are
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weakly basic
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Why does protonation of an acid on the carbonyl oxygen occur?
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A resonance stabilized cation is formed
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Why is protonation on the carboxylate oxygen much less favorable?
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It does not give a resonance-stabilized cation & positive charge on oxygen destabilized by polar effect of carbonyl group
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Fatty acids
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CA w long, unbranched C chains
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Saponification
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Liberation of fatty acids form fats and oils by a hydrolytic process
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Some fatty acids contain C=C that are
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cis (trans is rare in nature)
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soaps
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sodium & potassium salts of fatty acids
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detergent
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any substance used for cleaning an object by immersing it in a liquid solution
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surfactants
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mlcs w polar head group & hydrocarbon tail not readily solvated by h2o
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In a soap what is polar & hydrocarbon?
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polar head is carboxylate anion, hydrocarbon tail is C chain
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anionic surfactants
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surfactants w anionic polar head group
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cationic surfactants
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surfactant with cationic polar head group
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critical micelle conc
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concentration of surfactant at which mlcs spontaneously form micelles: spherical aggregates
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How do detergents work?
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dirt associates w hydrocarbon on interior of micelle & is incorporated into micellar aggregate, thus lifted away from surface of fabric carried into solution
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when a bacterial cell is exposed to a solution w a surfactant, phospholipids of cell membrane tend to
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associate w the surfactant, in some cases can disrupt the membrane enough that the cell can no longer function & dies
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typically run by pouring ether solution of grignard reagent over crushed dry ice
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Mechanism preparation CA
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Addition of grignard reagent to CO2 gives bromomagnesium salt of CA & aq. acid added => free CA
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substitution at the carbonyl carbon: most typical rxn @ carbonyl group
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rxn of carbonyl O w an electrophile (rxn of carbonyl O as a base)
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The reactions of nuc at the carbonyl carbons are catalyzed by
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reactions of acids at the carbonyl oxygen
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rxn @ carboxylate oxygen: ionization of CAs
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reaction of carboxylate oxygen as nuc
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decarboxylation
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loss of carboxy group as CO2
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Esters
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carboxylic acid derivatives
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acid catalyzed esterification/ Fischer esterification
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small equilibrium constant
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Fischer rxn driven to completion by
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using reactant alcohol as solvent (driven toward ester prod)
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Can acid-catalyzed esterification be applied to the synthesis of esters from phenols or tertiary alcohols?
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No: tertiary alcohols undergo dehydration & other rxns under acidic conditions & equil. constants for esterification of phenols much less favorable than those for alcohols
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Mechanism of acid-catalyzed esterification
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Substitution of OH at the carbonyl group of the acid by the oxygen of the alcohol
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Mechanism of acid-catalyzed esterification step 1
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protonation of a carbonyl O makes carbonyl C more
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electrophilic
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formation of tetrahedral addition intermediate
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essentially same as acid-catalyzed rxn of alcohol w protonated aldehyde or ketone to form hemiacetal
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tetrahedral addition intermediate reacts further
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protonated then loses water to give conjugate acid of ester
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Loss of a proton gives
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ester product, regenerates acid catalyst
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general substitution rxns of CAs
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Why don't ald/ket undergo sub @ carbonyl C?
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After nuc reacts @ carbonyl C, neither groups attached can act as LG bc would be expelled as H- or R- either of which is a very strong base
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When a carboxylic acid is treated with diazomethane in ether solution
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it is rapidly converted into its methyl ester
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ester formation mechanism
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protonation of diazomethane by CA gives methyldiazonium ion
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is dinitrogen a good or bad leaving group?
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GREAT
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Sn2 reaction of methyl-diazonium ion with carboxylate oxygen
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results in displacement of N2 & formation of ester
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Are carboxylate ions basic?
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Less nuc than alkoxides or phenoxides but react w reactive alkylating agents
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CA is required for reaction with diazomethane bc
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protonation of diazomethane is first step of reaction
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typically carried out in PA solvents that accelerate SN2 like acetone
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Sn2 rxn in which carboxylate ion reacts as nuc w alkyl halide - best on alkyl halides that are especially reactive in sn2 rxns such as methyl iodide & benzylic /allylic halides
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Acid chlorides
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cyclic anhydride
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P2O5
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inorganic anhydride used to form anhydrides of CAs
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Mechanism CA reduction
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LiALH4 reacts w acidic H of CA to give Li salt of CA + 1 equiv H2
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What species is reduced?
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The lithium salt of the CA
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Mechanism CA reduction 2
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AlH3 reduced carboxylate ion into an aldehyde, which is reduced to give after protonolysis, the primary alcohol
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The aldehyde cannot be isolated because
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it is more reactive than the carboxylate salt
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Net substitution followed by net addition
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Does NaBH4 reduce CA?
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No
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Decarboxylation
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loss of CO2 from a carboxylic acid
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b-keto acids
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CA w keto group in B position: readily decarboxylate @ room temp in acidic solution
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Enol intermediate formed by intermlcr transfer from CA group to carbonyl O atom of ketone
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enol transformed spontaneously into corresponding ketone
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The acid form of the B-keto acid decarboxylates more readily than the conjugate base carboxylate form because
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base has no acidic proton that can be donated to the B-carbonyl oxygen (promotes its own removal)
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Malonic acid: readily decarboxylates upon heating in acidic solution
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requires heating so acids can be isolated @ room temp
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Carbonic acid
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unstable, decarboxylates in acidic solution to co2 + h2o
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any carbonic acid derivative w a free carboxylic acid group will decarboxylate under acidic conditions
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Under basic conditions, carbonic acid & derivatives
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exist as carboxylate salts & do not decarboxylate
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Carbonic acid diesters & diamides are
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stable
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