Ch. 8: Carboxylic Acids Flashcards
defn: carboxylic acid
contains both a carbonyl group and a hydroxyl group, bonded to the same carbon
are carboxylic acids terminal groups?
always!
how are carboxylic acids named?
by adding the suffix -oic acid to the parent root when the carboxylic acid is the highest-priority functional group
the carbonyl C becomes C #1
how are cyclic carboxylic acids named?
by listing the cycloalkane with the suffix carboxylic acid
how are salts of carboxylic acids named?
beginning with the cation, followed by the name of the acid with the ending -oate replacing -oic acid
defn: dicarboxylic acids
have a carboxylic acid group on each end of the molecule
what is the smallest dicarboxylic acid?
oxalic acid (2 carbons)
what are the next 5 straight-chain dicarboxylic acids?
what suffix do their IUPAC names have?
malonic
succinic
glutaric
adipic
pimelic
acids
suffix: -dioic acid
what are the physical properties of carboxylic acids?
- many are similar to those of aldehydes and ketones because they both contain carbonyl groups
- however, the additional hydroxyl group permits carboxylic acids to hydrogen bond and provides another acidic hydrogen that can participate in reactions
why are carboxylic adis polar?
because they contain a carbonyl group
why can carboxylic acids form hydrogen bonds?
because they contain a hydrogen bonded to a very electronegative atom
why do carboxylic acids display particularly strong intermolecular interactions?
because both the hydroxyl oxygen and carbonyl oxygen can participate in hydrogen bonding
what is a result of the fact that carboxylic acids display strong intermolecular interactions?
they tend to form dimers
defn: dimers
pairs of molecules connected by two hydrogen bonds
why do carboxylic acids have elevated boiling points and melting points compared to corresponding alcohols? (2)
multiple hydrogen bonds AND increasing molecular weight
what causes a very stable carboxylate anion? (3)
- the hydroxyl hydrogen of a carboxylic acid is quite acidic
- thus there is a negative charge that remains after the H is removed and resonance stabilization occurs between both of the electronegative O atoms
- delocalization of the negative charge causes a very stable carboxylate anion
what things contribute to the acidity of a carboxylic acid and how?
- the more stable the conjugate base is, the easier it is for the proton to leave, thus the stronger the acid –> carboxylic acids are relatively acidic
- substituents on carbon atoms near a carboxyl group influence anion stability and therefore affect acidity
give 2 examples of electron-withdrawing groups and electron-donating groups. what affect do each of these types of groups have?
electron-withdrawing = -NO2, halides –> increase acidity
electron-donating: -NH2, -OCH3 = destabilize the negative charge, decreasing the acidity
how does the proximity to the carboxyl group of the substituent groups that are electron-withdrawing or electron-donating affect their impact?
the closer they are, the greater the effect
in dicarboxylic acids, does each -COOH group influence each other?
yes
why are carboxylic acids electron-withdrawing?
due to the electronegative oxygen atoms they contain
what is the net result of the fact that the -COOH groups in dicarboxylic acids influence each other and the fact that carboxylic acids are electron-withdrawing?
dicarboxylic acids are more acidic than the analogous monocarboxylic acids
when one proton is removed from a dicarboxylic acid, and the carboxylate anion is formed, how is acidity impacted?
there is an immediate decrease in the acidity of the remaining carboxylic acid
why is the second proton of the carboxylate anion (previously dicarboxylic acid) harder to remove than the analogous proton of a monocarboxylic acid?
harder to remove - less acidic
if the second group were deprotonated on the carboxylate anion, it would create a doubly charged species with two negative charges repellinge ach other
defn + char (1): beta-dicarboxylic acids
dicarboxylic acids in which each carboxylic acid is positioned on the beta-carbon on the other
aka: there are two carboxylic acids separated by a single carbon
they are notable for the high acidity of the alpha-hydrogens located on the carbon between the two carboxyl groups
what results when you lose the acidic H on the C between the two carboxyl groups in beta-dicarboxylic acids?
produces a carbanion, which is stabilized by the electron-withdrawing effect of both carboxyl groups
what other 4 types of alpha-H compounds does this apply to?
+ structure
- beta-diketone
- beta-ketoacids
- beta-dialdehydes
- other molecules that share the 1,3-dicarbonyl structure
how are carboxylic acids prepared?
via oxidation of aldehydes and primary alcohols
what are the three main oxidants/oxidizing agents in the synthesis of carboxylic acids?
- dichromate salt (Na2Cr2O7 or K2Cr2O7)
- chromium trioxide (CrO3)
- potassium permanganate (KMnO4)
can secondary and tertiary alcohols be oxidized to carboxylic acids? why or why not?
NO bc they already have at least 2 bonds to other carbons
what are two other methods of generating carboxylic acids that are outside the scope of the MCAT?
- organometallic reagents (Grignard reagents)
- hydrolysis of nitriles (-C—N) –> triple bond
what is the single mechanism that many of the reactions in which carboxylic acids and their derivatives participate?
nucleophilic acyl substitution
what mechanism is nucleophilic acyl substitution similar to? where is the difference?
nucleophilic addition to an aldehyde or ketone
the key difference focuses on the existence of a leaving group in carboxylic acids and their derivatives
process (2): nucleophilic acyl substitution
- nucleophilic addition (open the carbonyl via nucleophilic attack to form) a tetrahedral intermediate
- reformation of the carbonyl, which thereby kicks off the LG
in nucleophilic acyl substitutions, what does the nucleophilic molecule replace?
the nucleophilic molecule replaces the leaving group of an acyl derivative
defn: acyl derivatives
all molecules with a carboxylic acid-derived carbonyl, including carboxylic acids, amides, esters, anhydrides, and others
what conditions (2) favor nucleophilic acyl substitution reaction?
- good leaving groups
- acidic or basic conditions (which can alter the reactivity of the electrophile and nucleophile)
what make good leaving groups?
weak bases
how can carboxylic acids be converted into amides? what type of solution should this be carried out in?
if the incoming nucleophile is ammonia (NH3) or amine
can be carried out in acidic or basic solution to drive the reaction forward
how are amides named?
by replacing the -oic acid suffix with -amide in the name of the parent carboxylic acid
any alkyl groups on the nitrogen are placed at the beginning of the name with the prefix N-
what does it mean that amides exist in a resonance state?
delocalization of electrons occurs between the oxygen and nitrogen
resonance between the carbonyl and lone pair on the nitrogen stabilizes the bond and restricts its mostion
defn: lactam
cyclic amides
how are lactams named?
by replacing -oic acid with -lactam
can also be named by indicating the specific carbon that is bonded during cyclization of the compound
defn: ester
a hybrid between a carboxylic acid and an ether (ROR’)
how can carboxylic acids be converted into esters?
react carboxylic acids with alcohols under acidic conditions
defn + process in acidic solutions: esterification
with what functional group does this reaction occur most rapidly?
a condensation reaction with water as a side product
in acidic solutions: the carbonyl O can be protonated –> enhances the bond’s polarity –> places additional positive charge on the carbonyl C –> increases its susceptibility to nucleophilic attack
occurs most rapidly with primary alcohols
how are esters named?
the same way as salts of carboxylic acids
defn: lactone
cyclic ester
how are lactones named?
replace -oic acid with -lactone
how are anhydrides formed?
by the condensation of two carboxylic acids
how are anhydrides named?
by placing the acid at the end of the name of the parent carboxylic acid with anhydride (cyclic or linear)
how are carboxylic acids reduced? to what? how?
they are reduced to primary alcohols
by the use of lithium aluminum hydride (LiAlH4)
occurs by nucleophilic addition of hydride to the carbonyl group, and proceeds through an aldehyde intermediate
why is LiAlH4 used to reduce carboxylic acids? why not use NaBH4?
it is a strong reducing agent
NaBH4 is not strong enough (sodium borohydride)
defn + func: carboxylation
the complete loss of the carboxyl group as carbon dioxide
a common way of getting rid of a carbon from the parent chain
common in the body’s biochemical pathways
what two kinds of acids may spontaneously decarboxylate when heated? how (3)?
1,2-Dicarboxylic acids
other B-keto acids
- the carboxyl group is lost and replaced with hydrogen
- because both the electrophile and nucleophile are in the same molecule, the reaction proceeds through a 6-membered ring in its transition state
- the enol that is initially formed from the destruction of the ring tautomerizes to the more stable keto form
defn: saponification
when a salt is formed by reacting long-chain carboxylic acids with sodium or potassium hydroxide
occurs by mixing fatty acids with lye (sodium or potassium hydroxide) –> forms a salt known as soap
why can soaps solvate nonpolar organic compounds in aqueous solutions? ex.
because they contain a nonpolar tail and a polar carboxylate head
what happens to soap molecules when placed in aqueous solutions?
they arrange themselves into spherical structures (micelles)
structure: micelle
polar heads face outward (can be solvated by water)
nonpolar hydrocarbon chains oriented inside the sphere (protected from the solvent)
explain how a micelle interacts with a nonpolar molecule, like grease
nonpolar molecules (like grease) dissolve in the hydrocarbon interior of the spherical micelle, the micelle as a whole then dissolves in water due to the exterior’s polarity
