Chem 150 Unit 7 - Organic Molecules II Carboxylic Acids, Phenols & Amines

Chem 150Unit 7 - Organic Molecules IICarboxylic Acids, Phenols & Amines • In this unit and the next we look at the chemical and physical properties of a variety of organic families, all of which play important roles in biochemistry. These include the carboxylic acids, phenols, amines and amides. We also look at a new type of stereoisomer that figures predominantly in biological chemistry; the optical isomer.

Introduction • The organic groups covered in this Unit all have important biological roles • Carboxylic acids • Fatty acids • Amino acids and proteins • Phenols • Colors and flavorings • Amino acids and proteins • Signal molecules • Amines • Amino acids and proteins • Signal molecules • Drugs • Amides • Amino acids and proteins

Carboxylic Acids • Naming carboxylic acids • The IUPAC ending is -oic acid.

Question • Give the IUPAC names for the following carboxylic acids:

Carboxylic Acids • Carboxylic acid have high melting points • Small carboxylic acids are quite soluble in water

Carboxylic Acids • Small (volatile) carboxylic acids have noticeable odors. • Ethanoic acid (acetic acid) vinegar • Butanoic acid (butyric acid) vomit, dirty socks • Hexanoic acid (caproic acid) goats, ripe cheese

Phenols • Simplest phenol is phenol. • A hydroxyl group attached to a benzene ring.

Phenols • All phenols contain hydroxyl groups attached to aromatic rings.

These have 2 hydroxyl groups attached to a benzene ring

Carboxylic Acids & Phenols as Weak Acids • Both carboxylic acids and phenols are weak acids pKa ≈ 5 pKa ≈ 10

Carboxylic Acids & Phenols as Weak Acids • The acidity of hydroxyl groups depend on what they are connected to:

Carboxylic Acids & Phenols as Weak Acids • At pH 7, the carboxylate ion of carboxylic acids predominate • At pH 7, the phenol of phenol predominate pH = 7 pKa ≈ 5 pH = 7 pKa ≈ 10

Carboxylic Acids & Phenols as Weak Acids • Strong bases can be used to convert carboxylic acids and phenols to their corresponding carboxylate and phenoxide ions

Carboxylic Acids & Phenols as Weak Acids • Fatty acids are carboxylate ions at pH 7 • Fatty acids with less that 12 carbons are soluble in water • Fatty acids with greater than 12 carbons are amphipathic, and form micelles when mixed with water.

Carboxylic Acids & Phenols as Weak Acids • IUPAC names for carboxylate ions: • Remove the “-ic acid” from the corresponding conjugate acids name and replace it with “-ate ion”.

Carboxylic Acids & Phenols as Weak Acids • Examples:

Carboxylic Acids & Phenols, Other Reactions • We have already seen how carboxylic acids and carboxylate ions can be made from from the hydrolysis of esters. • Base-catalyzed hydrolysis of esters: • Acid-catalyzed hydrolysis of esters:

Carboxylic Acids & Phenols, Other Reactions • The acid-catalyzed hydrolysis of esters is reversible and can be used to make esters from carboxylic acids and alcohols: • Synthesis of esters from carboxylic acids and alcohols:

Carboxylic Acids & Phenols, Other Reactions • A biologically important reaction involving carboxylic acids is the decarboxylationof α-keto and β-keto acids:

Carboxylic Acids & Phenols, Other Reactions • The decarboxylation of β-keto acids produces ketones • The decarboxylation of α-keto acids produces aldehydes

Carboxylic Acids & Phenols, Other Reactions • The oxidation of hydroquinones is also an important biological reaction. • A chemical oxidation of hydroquinones can be carried out the oxidizing agent K2Cr2O7 (potassium dichromate)

Carboxylic Acids & Phenols, Other Reactions • Example: • Coenzyme Q and the Electron Transport Chain

Amines • Amines are a nitrogen with one or more carbons attached: • Amines are classified based on the number of carbons that are attached to the nitrogen. • Primary amine (1°): 1 carbons • Secondary amine (2°): 2 carbons • Tertiary amine (3°): 3 carbons

Amines • It is possible for a fourth carbon to attach to the nitrogen • The nitrogen will take on a positive charge to become an ion. • Quaternary (4°) ammonium ions: 4 carbon atoms

Amines

Amines • The IUPAC names for 1°, 2°, and 3° amines. • Create the parent name by picking the longest chain of carbons that is attached to the nitrogen. • Replace the “-e” in the parent with the ending “-amine”. • Number the longest chain from the end that gets you to the the carbon to which the nitrogen is attached in the fewest number of carbons. • Use a numbered prefix to indicate which the carbon in the longest chain the nitrogen is bonded to. • If other substituents are attached to the nitrogen, list them and use the prefix “N-” to indicate that they are attached to the nitrogen.

Questions • Give the IUPAC names for the following amines:

Questions • Give the IUPAC names for the following amines: 2-butanamine 2-butanamine N-ethyl- N-propyl N-ethyl-N-propyl-2-butanamine

Amines • For heterocyclic amines the nitrogen is part of a ring. • The ring can be either aromatic or not. • The nucleic acid nucleotide bases are good examples of hetoercyclic amines

Amines • Hydrogen Bonding • 1° and 2° amines can serve as both a hydrogen bond donor and acceptor. • 3° amines can server as a hydrogen bond acceptors, but not donors.

Amines • Hydrogen Bonding • 4° ammonium ion cannot form hydrogen bonds, but because they are charged, form ionic bonds:

Amines • The ability to hydrogen bond give amines moderately high boiling points and high solubilities in water.

Amines • Another notable property of amines is their odor. • Like carboxylic acids, they can also produce foul odor. • The produce a “fishy” smell. • Examples of amines, whose names imply their odoriferous properties, include

Amines as Weak Bases • In Unit 6, while discussing the definitions of acids and bases, we saw that ammonia, NH3, is operationally a base • That is, when added to water ammonia causes the pH to rise above pH 7. • Ammonia was the example we used to demonstrate the need for the Brønsted-Lowry definition of acids and bases. See the Unit 6 Elaboration -Definitions of Acids and Bases - Part III:Brønsted-Lowry Definition

Amines as Weak Bases • Like ammonia, 1°, 2° and 3°, act as Brønsted-Lowry bases.

Amines as Weak Bases • The conjugate acids are called ammonium ions • When placed in water, these ammonium ions will behave like acids.

Amines as Weak Bases • Because it is charged, the conjugate acid is even more soluble that the amine. • Many drugs are amines and are sold the ammonium salts, which are more readily absorbed, due to their increased solubility. • Ephedrine is used as a decongestant.

Amines as Weak Bases • Ephedrine is an example of an alkaloid. • Alkaloids are alkaline molecules that are derived from plants. • “alkaline” and another name for basic. • Ephedrine is isolated from the Chinese ma huang plant(Ephedra sinica)hyperlink

Amides • When a carboxylic acid reacts with an amine it also produces and ammonium salt • If the ammonium salt is then heated, an amide is produced.

Amides • Amides are important in biochemistry. • For example, amino acids are connected together to form proteins using amide groups. amino acid

Amides • Amides can be hydrolyzed back to carboxylic acids and amines by heating them in the presence of an acid

Stereoisomers • So far we have encountered two different types of isomers. • Constitutional Isomers • Stereoisomers • cis/trans isomers with alkenes and cycloalkanes, that arise from restricted rotation about bonds. • There is one more type of stereoisomer, which is important in biochemistry. • optical isomers

Stereoisomers • Optical isomers arise when a carbon atom has four different things attached to it. • These carbons are called chiral carbons. • The a molecule containing a chiral carbon is non superimposable on its mirror image. • The molecule and its mirror image are referred to as enantiomers

Stereoisomers

Chem 150 Unit 7 - Organic Molecules II Carboxylic Acids, Phenols & Amines