ORGANIC CHEMISTRY
Alcohols
ETHANOL
Ethanol is produced from the fermentation of
glucose
 Glucose is often derived from the hydrolysis of
more complex carbohydrates
 (C6H10O5)n + nH2O  nC6H12O6


C12H22O11 + H2O  2C6H12O6

C6H12O6  2C2H5OH + 2CO2
YEAST


Yeast is a micro organism that acts as a catalyst
Optimum conditions for fermentation rely on
three main factors
Optimum temperature is between 20o – 30o
 Optimum pH is mildly acidic (pH 6.1 - 6.8)
 Anaerobic conditions

PRIMARY, SECONDARY AND TERTIARY

A hydroxyl group is defined according to the
number of carbon-carbon bonds on the carbon it
is directly bonded to
(note methanol is considered primary)
OXIDATION OF ALCOHOLS
We can use oxidation to differentiate between
primary, secondary and tertiary alcohols
 Cr2O72- is commonly used in this oxidation
 Primary alcohol oxidises to an aldehyde, which in
turn is oxidised to a carboxylic acid
 Secondary alcohol oxidises to a ketone
 Tertiary alcohol does not oxidise

OXIDATION CONDITIONS
Acidified (potassium) dichromate solution
 Reaction must be heated
 Cr2O72-/H+ written above the arrow, heat written
below
 Change in colour due to reduction of orange
dichromate ions to green chromium ions (Cr3+)
 The aldehyde to carboxylic acid reaction will
continue in the same flask unless distilled off

ORGANIC CHEMISTRY
Aldehydes and Ketones
PREPARATION: ALDEHYDES



Controlled oxidation of primary alcohols
Distillation apparatus is used with a separating
funnel to add the oxidising agent
The aldehyde boils off first due to its lower
boiling point
PREPARATION: KETONES



Oxidation of secondary alcohols
Ketones do not oxidise further and so do not need
to be distilled
Prepared via reflux with oxidising agent
DISTINGUISHING TESTS
Rely on aldehyde oxidising and ketone not
 Heating with acidified potassium dichromate



Orange > green = positive for aldehyde
Ammoniacal silver nitrate (Tollen’s reagent)
Silver mirror = positive for aldehyde
 Weak oxidiser, so does not oxidise alcohols


Carbohydrates able to form straight chains act as
aldehydes / ketones for these tests
DISTINGUISHING TESTS

The dichromate oxidation occurs in acidic
conditions, therefor the product is a carboxylic
acid
RCHO
 Cr2O72

RCOOH
Cr3+
The Tollen’s reagent oxidation occurs in basic
conditions, therefor the product is a carboxylate
ion
RCHO
 Ag(NH3)2+

RCOOAg
ORGANIC CHEMISTRY
Carbohydrates
DEFINITION



Carbohydrates are naturally occurring
substances with a general formula Cx(H2O)y
They are defined as polyhydroxyaldehydes or
polyhydroxyketones or compounds that produce
these when hydrolysed
They are also classified as monosaccharides,
disaccharides or polysaccharides depending on
the number of simple sugar units.
MONOSACCHARIDES
Water soluble
 Sweet taste, often referred to as simple sugars
 Structurally can exist as chain or cyclic forms.

The forms exist in equilibrium
 In aqueous solution the equilibrium lies very much in
favour of the cyclic form


Solids at room temperature
DISACCHARIDES
Water soluble
 Two monosaccharide units per molecule
 Formed by condensation of monosaccharides or
hydrolysis of polysaccharides
 For each pair of monosaccharides there are
numerous disaccharides possible, eg there are
four glucose-glucose disaccharides

POLYSACCHARIDES
Insoluble in water
 Can absorb water
 Formed from many repeating units of
monosaccharide
 Examples include starch, cellulose and glycogen

CHAIN AND RING STRUCTURES
Glucose exists as an equilibrium between its
chain and ring forms
 Glucose can react as an aldehyde (eg Tollens)

SOLUBILITY

Remember, solubility relies on two things:
Functional group – secondary bonds
 Molecular size

Carbohydrates are polyhydroxy and can form
multiple hydrogen bonds
 Only mono and disaccharides are small enough to
mix with water and form aqueous solutions
 Some carbohydrates can instead absorb water

ORGANIC CHEMISTRY
Carboxylic Acids
CARBOXYLIC ACIDS

Common in many molecules





Formic acid – bee and ant stings
Acetyl salicyclic acid – aspirin
Ibuprofen
Acetic acid – vinegar
Citric acid – fruits
SOLUBILITY AND BOILING POINT
Highly polar functional group
 Small carboxylic acids are soluble
 Solubility can be increased by forming a
carboxylate salt
 Higher boiling points than their corresponding
alcohols and aldehydes

ODOR AND TASTE

Carboxylic acids tend to have strong odors
Acetic acid
 Many perfumes


In many foods
Food acid tends to be carboxylic acid
 Vinegar (sour)
 Citric (sharp)

PREPARATION

Prepared from either primary alcohol or aldehyde

Reflux with acidified potassium dichromate

You will need to be able to explain the purpose of
reflux
REACTIONS
Act as weak acids
 Ionize to carboxylate anions in water

Reminders
 Acid + base -> salt + water
 Acid + carbonate -> salt + carbon dioxide + water
 Acid + hydrogen carbonate -> salt + water
+ carbon dioxide

ORGANIC CHEMISTRY
Esters
USES
Esters are the cause of many fruity odours, such
as in fruits and wines
 Esters are good solvents and are used in many
paints and lacquers
 Used in perfumes, cosmetics and artificial
flavours
 Animal fats and vegetable oils are esters of
propan-1,2,3-triol

NAMING
Named for their corresponding carboxylic acids
and alcohols
 Alcohol group is given suffix –yl
 Carboxylic acid group is given suffix –anoate
 To pick which part was the carboxylic acid, look
for the carbonyl group

SOLUBILITY AND BOILING POINT
Esters are less polar than their corresponding
alcohols or carboxylic acids
 Dipole-dipole interactions are weaker than the
hydrogen bonds present in alcohols and
carboxylic acids
 Hence the boiling point and water solubility of
esters is lower than either carboxylic acids or
alcohols

PREPARATION
Reacting an alcohol with a carboxylic acid under
reflux with sulfuric acid catalyst
 Esterfication is an example of a condensation
reaction
 Sulfuric acid acts as both a catalyst and a
dehydrating agent, forcing the equilibrium to the
products
 Esterfication is an equilibrium reaction. Excess of
alcohol can force towards products

REFLUX
Reflux allows extended period of heating without
loss of reactants
 Heating required to increase the rate of slow
reactions

HYDROLYSIS
The reverse of esterfication
 Reflux under either acidic or basic conditions
 Acidic conditions

Form carboxylic acid and alcohol
 Excess water favours formation of carboxylic acid and
alcohol


Basic conditions
Form caboxylate salt and alcohol
 Non reversible and easier to separate products

ORGANIC CHEMISTRY
Triglycerides
TRIGLYCERIDES
Triglycerides are esters of fatty acids and propan1,2,3-triol (glycerol)
 Liquid triglycerides are oils, solid triglycerides
are fats

FATTY ACID

A fatty acid has the following general structure
O
C
Long hydrocarbon chain
Nonpolar tail
OH
Carboxyl end
Polar head
HYDROLYSIS

Like all esters, triglycerides can undergo
hydrolysis
SATURATED FATS

Saturated fats have no double or triple bonds in
their fatty acid tail

ie they are saturated with hydrogen

Generally solids at room temperature

Major source is animal fats
UNSATURATED FATS

Contain one or more double bonds

Generally liquids at room temperature

Vegetable oils are a major source
MELTING POINTS
Melting and boiling points vary according to two
factors
 Molecular weight



Longer chains lead to higher mp, due to the greater
dispersion forces
Saturation
The more unsaturated the fatty acid, the looser the
chains pack together.
 Because distance between the chains is greater,
dispersion forces are reduced

DEGREE OF UNSATURATION
The degree of unsaturation of a fatty acid can be
found by an addition reaction with a diatomic
molecule (Br2, I2, H2)
 Br2 is the most common way as it has a
distinctive colour (orange)
 A Br2 standard solution (in cyclohexane) can be
used to titrate the fat or oil
 Degree of unsaturation often referred to as iodine
number

HYDROGENATION
Liquid oils can be converted to solid fats through
hydrogenation
 Reaction rate increased by

High temperature
 High pressure
 Ni catalyst

ORGANIC CHEMISTRY
Amines and Amides
AMINES
Amines are derivatives of ammonia
 One or more hydrogens from ammonia can be
replaced with alkyl groups
 They are classified as primary, secondary or
tertiary depending on the number of hydrogens
replaced

AMINES AS BASES
N on amine has unbonded pair of electrons that
can accept a proton
 When an amine molecule accepts a proton a
positively charged ammonium ion is formed

PROTONATED AMINES
Protonated amines form strong ion-dipole
secondary bonds
 This can be used to improve drug solubility
(similar to carboxylate salts)

AMIDE

Amides have the following structure
PREPARATION OF AMIDES


Theoretically produced by condensation reaction
of amine and carboxylic acid
In practice the acid reacts with the amine to form
an ammonium salt
Heat ammonium carboxylate above melting point
 Reflux ester with amine

HYDROLYSIS OF AMIDES
Hydrolysis can occur under both acidic and basic
conditions
 Acidic

Reflux with dilute acid (eg HCl)
 Product is carboxylic acid and ammonium ion


Basic
Reflux with base (eg NaOH)
 Product is carboxylate ion and amine

ORGANIC CHEMISTRY
Proteins
Amino Acids
Proteins are polymers of amino acids
 Most amino acids have four groups bonded to a
central carbon atom: a carboxyl group, an amino
group, an R group and a hydrogen

Amino Acids
The chemical nature of the side chain accounts
for the different chemical properties
 Hundreds are possible, but twenty are found in
the human body
 Essential amino acids are those that cannot be
synthesised in the body (and so must come from
our diet)

Zwitterions
Many physical and chemical properties are not
consistent with the H2N-CHR-COOH structure
 The weakly acidic proton of the carboxyl group
transfers to the amino group
 Forms a dipole ion or zwitterion
 In pure solid state and neutral solutions they
exist almost completely as zwitterions
 They are amphoteric

Peptides
Amino acids react to form peptides, a special
form of polyamide
 The carboxyl group reacts in a polymerisation
(condensation) reaction with the amino group of
another amino acid, forming a peptide or amide
linkage
 Can form dipeptides, tripeptides up to
polypeptides
 Peptides up to 10 000 g mol-1 (80-100 amino acid
units) are known as polypeptides, above that as
proteins

Structure

Primary Structure


Secondary Structure


The order of amino acids in the polypeptide chain
Hydrogen bonding between carboxyl and amine groups
causes the chain to bend into coils, pleats or folds
Tertiary Structure
Bonding between side chains result in complex three
dimensional shapes
 Can involve hydrogen bonding, ionic bonding or disulfide
bridges


Quaternary Structure
The shape determines the proteins properties and function
 Quaternary structure formed when individual protein
molecules link together

Enzymes
Organic catalysts
 Speed up the reaction by offering an alternative
reaction pathway with lowered activation energy
 Each enzyme has a unique 3D structure
 The active site is where the substrate is
converted into a product molecule
 Hold the substrate in place in a variety of ways
including hydrogen bonds and electrostatic forces
and often change throughout the reaction
 These multiple interaction make the enzyme
specific and will often catalyse only one reaction

Enzymes
Enzymes are able to operate only at body
temperatures and have an optimal pH range
 Variance in these ranges can cause them to
denature
 Denaturation is the disruption of inter and intramolecular bonds that maintain the shape and
structure of the enzyme
