Chapter 8: Carboxylic Acids Flashcards
(47 cards)
What are three ways that carboxylic acids react?
Are they important for amino acids?
What is the mean ingredient in vinegar?
What gives Swiss cheese it smell?
What is found in rancid butter and body odor?
Carboxylic acids can react as acids
Nucleophiles
Electrophiles
Amino acids have an amine group and a carboxylic acid group.
Acetic acid (ethanoic acid) is the main ingredient in vinegar
Propionic acid (propanoic acid) give Swiss cheese it smell
Butyric acid (butanoic acid) is founded rancid butter and body odor
What makes carboxylic acid so interesting and versatile?
What is the general pKa of carboxylic acids (and alcohols for comparison)
They are acids. They like to give away protons, particularly because when they do so, the remaining negative charge resonates between two oxygen atoms, making the anion very stable. This makes carbonic acid some of the most acidic compounds encountered in organic chemistry
pKa of carboxylic acid is between three and six
pKa of alcohol are around 17
Excellent at hydrogen bonding, resulting in large intermolecular forces in high boiling points
Ubiquitous in nature and are synthesized by all living organisms
Are carboxylic acids always terminal groups?
How many bonds to oxygen does a carboxylic acid functional group have?
Carboxylic acids are always terminal groups
Carboxylic acid functional groups have three bonds to oxygen atoms, making it one of the most oxidized functional groups encountered in organic chemistry
How do we name carboxylic acids?
Suffix -oic acid to the parent root when the carboxylic acid is the highest priority functional group
When this is true, the carbonyl carbon becomes carbon number one
Cyclic carboxylic acids are named by listing the cycloalkane with the suffix carboxylic acid
Salts of carboxylic acids are named beginning with the cation, followed by the name of the acid with an ending -oate replacing -oic acid
How do we name dicarboxylic acids?
Draw ethanedioic acid (oxalic acid), propanedioic acid (malonic acid), butanedioic acid (succinic acid), glutaric acid (pentane dioic acid), adipic acid (hexanedioic acid), pimelic acid (heptane dioic acid)
Dicarboxylic acids, which have a carboxylic acid group on each end of the molecule, are common in biological systems.
The smallest dicarboxylic acid is oxalic acid, then malonic, succinic, glutaric, adipic, pimelic acids.
Have the suffix -dioic acid
What are the physical properties of carboxylic acids?
Similar to aldehydes and ketones because they both contain carbonyl groups.
However, the additional hydroxyl group permit carboxylic acid to hydrogen bond and provides another acidic hydrogen that can participate in reactions.
Display particularly strong in intermolecular attractions because both the hydroxyl oxygen and the carbonyl oxygen can participate in hydrogen bonding
Carboxylic acids have elevated boiling point and elevated melting point passed those of corresponding alcohols
Boiling point increases with increasing molecular weight
Throwback. Can aldehydes and ketones participate in hydrogen bonding?
They cannot participate in hydrogen bonding with themselves, can form weak hydrogen bonds with water
Aldehydes and ketones lack the necessary hydrogen bonded to an electronegative species
Do carboxylic acids form dimers?
Why?
Carboxylic acids display particularly strong, intermolecular retractions because both the hydroxyl oxygen and carbonyl oxygen can participate in hydrogen bonding
As a result, carboxylic acids tend to form dimers: pairs of molecules connected by two hydrogen bonds
Multiple hydrogen bonds elevate the boiling and melting point of carboxylic acids past those of corresponding alcohols
One has a higher boiling point: oxalic acid or succinic acid?
Due to succinic acid being larger (4C) than oxalic acid (2C), succinic acid has the higher boiling point
Carboxylic acids are polar and can form hydrogen bonds
What is there acidity due to?
Carboxylic acid acidity is due to resonance stabilization and can be enhanced by the addition of electronegative groups or a greater ability to delocalize charge
Are carboxylate anions stable?
Yes
They are conjugate base of a strong acid and therefore stable (weak)
The localization of the negative charge results in a very stable carboxylate ion
Resonance stabilization occurs between both of the electronegative oxygen atoms
What is the tend for acidity of carboxylic acids?
The more stable the conjugate base is the easier it is for the proton to leave, thus a stronger acid
The smaller the carboxylic acid, the more acidic it is (acetic acid: pKa=4.8 ; propionic acid: pKa=4.9)
Electron withdrawing groups (halides, -NO2) increase acidity
Electron donating groups (-NH2, -OCH3) the destabilize the negative charge decrease the acidity of the carboxylic acid compound
The closer the substituent groups are to the carboxyl group, the greater the effect will be
What is the trend for acidity of dicarboxylic acids and monocarboxylic acids?
In dicarboxykic acids, each -COOH Group influences the other -COOH Group
Carboxylic acids are electron with withdrawing due to the electronegative oxygen atoms they contain
The net result is that dicarboxylic acids are more acidic than the analogous monocarboxylic acid
However, the second proton of a dicarboxylic acid is less acidic (harder to remove) then the analogous proton of a monocarboxylic acid
What are beta dicarboxylic acids?
General pKa?
Two carboxylic acids positioned on the same molecule, separated by only one carbon
Diarboxylic acids in which each carboxylic acid is positioned on the beta carbon of the other
General pKa of 9 to 14
Loss of acidic hydrogen produces a carbanion which is stabilized by the electron withdrawing effect of both carboxyl groups
Concept check 8.1
How do we synthesize carboxylic acid?
By oxidizing a primary alcohol
Remember the secondary tertiary alcohols cannot be oxidized to carboxylic acids because they already have at least two bonds to other carbons
Draw generic nucleophilic acyl substitution
What is it?
Nucleophilic acyl substitution: nucleophile attacks carbonyl carbon, forming tetrahedral intermediate, kicking off a leaving group
What is an acyl derivative?
Acyl derivatives, encompass all molecules with a carboxylic acid derived carbonyl: carboxylic acids, amides, esters, anhydrides, etc.
Favored by a good leaving group
Remember that weak bases (which are conjugate bases of strong acids) make good leaving groups
What is an acyl group?
An acyl group is any R attached to a carbonyl group.
Acyl halides, for example, are an RCO-Cl (note that Cl is placed for generic halide)
Draw formation of an amide by nucleophilic acyl substitution
Carboxylic acids can be converted into amides if the incoming nucleophile is ammonia (NH3) or an amine
What is an amides? Amine? Ammonia?
Amide: RCO-N group
Amine: N containing organic compound
Ammonia: NH3
How do we name amides?
Replace -oic acid 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-
Amides exist in a resident state or the localization of electrons occurs between the oxygen and nitrogen atoms
What is a lactam?
How do we name amides that are cyclic?
Amides that are cyclic are called lactams.
Named by replacing -oic acid with -lactam
What is an ester?
Esters or a hybrid between a carboxylic acid and an ether (ROR’)
Made by reacting carboxylic acids with alcohols under acidic conditions
Esterification is a condensation reaction with water as a side product
