Download Esters, fats and oils

Higher Chemistry - Traffic Lights
Unit 2 NATURE’S CHEMISTRY
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Esters, fats and oils
Esters
1.
The functional group in esters is - COO- .
2.
Esters can be identified from the –‘yl -oate’ endings.
3.
Esters can be named from the names of the carboxylic acid and alcohol used to
make them e.g. methyl ethanoate is made from ethanoic acid and methanol.
4.
Esters can be named from structural formulae.
5.
Structural formulae for esters can be drawn, if given the names of the parent
alcohol and carboxylic acid or the name of the ester.
6.
Esters have characteristic smells making them useful as flavourings and
fragrances.
7.
Esters are also used as industrial solvents.
Making esters
1.
Esters are formed by a condensation reaction between a carboxylic acid and an
alcohol.
2.
The ester link, -COO-, is formed by the reaction of a hydroxyl group with a
carboxyl group.
3.
In condensation reactions, the molecules join together with the elimination of a
small molecule, in this case water.
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Hydrolysis of esters
1.
Esters can be hydrolysed producing a carboxylic acid and alcohol.
2.
The hydrolysis products can be named and their structural formulae drawn, given
the name of an ester or its structural formula
3.
The parent carboxylic acid and alcohol can be obtained by hydrolysis of an ester.
4.
In a hydrolysis reaction, a molecule reacts with water breaking down into smaller
molecules.
Fats and oils
1.
Fats and oils are a concentrated source of energy.
2.
Fats and oils are essential for the transport and storage of fat-soluble vitamins in
the body.
3.
Fats and oils are tri- esters formed from the condensation of glycerol (propane1,2,3-triol) and three carboxylic acid molecules.
4.
The hydrolysis products of a fat or oil can be identified from the structure of the
fat or oil.
5.
The carboxylic acids in fats and oils are known as ‘fatty acids’.
6.
Fatty acids can be saturated or unsaturated straight-chain carboxylic acids,
usually with long chains of carbon atoms.
7.
The lower melting points of oils, compared to those of fats, is due to a greater
degree of unsaturation of oil molecules.
8.
The low melting points of oils are due to the shapes of the molecules, preventing
close packing.
9.
The lack of close packing in oils means weaker van der Waals’ forces of
attraction compared to those in fats.
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Proteins
1.
Proteins are the major structural materials of animal tissue.
2.
Proteins are also involved in the maintenance and regulation of life processes.
3.
Enzymes are proteins.
4.
Amino acids are the building blocks from which proteins are formed.
5.
Amino acids are relatively small molecules which all contain an amino group
(NH2) and a carboxyl group (COOH).
6.
The body cannot make all amino acids required for body proteins so is dependent
on dietary protein for supply of certain amino acids.
7.
Proteins which must be taken in in the diet are known as essential amino acids.
8.
Proteins are made of many amino acid molecules linked together by
condensation reactions.
9.
In these condensation reactions, the amino group on one amino acid and the
carboxyl group on a neighbouring amino acid join together, eliminating water.
10.
The link which forms between the two amino acids can be recognised as an
amide link (CONH) also known as the peptide link.
11.
The structure of a section of a protein can be drawn from the structural formulae
of given amino acids.
12.
Differing sequences of just 26 amino acids can join together to make proteins
which fulfil different roles in the body.
13.
During digestion, enzyme hydrolysis of dietary proteins can produce amino acids.
14.
These amino acids can be identified by chromatography.
15.
The structural formulae of amino acids obtained from the hydrolysis of proteins
can be identified from the structure of a section of the protein.
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Chemistry of cooking
1.
The solubility of a molecule in water or fat/oil can be predicted from the functional
group present.
2.
The volatility of a molecule can be predicted from its size and the functional
groups present.
Aldehydes and ketones
1.
Many flavour and aroma molecules are aldehydes.
2.
Aldehydes and ketones both contain the carbonyl functional group, -C=O.
3.
Aldehydes can be identified from the ‘-al’ name ending.
4.
Ketones can be identified from the ‘-one’ name ending.
5.
Straight-chain and branched-chain aldehydes and ketones, with up to eight
carbon atoms in their longest chain, can be named from structural formulae.
6.
Given the names of straight-chain or branched-chain aldehydes and ketones,
structural formulae can be drawn and molecular formulae written.
7.
Aldehydes, but not ketones, can be oxidised to carboxylic acids.
8..
Fehling’s solution, Tollens’ reagent and acidified dichromate solution can be used
to differentiate between an aldehyde and a ketone.
Proteins
8.
Within proteins, the long-chain molecules may be twisted to form spirals, folded
into sheets, or wound around to form other complex shapes.
9.
The chains are held in these forms by intermolecular bonding between the side
chains of the constituent amino acids.
10.
When proteins are heated, during cooking, these intermolecular bonds are
broken allowing the proteins to change shape (denature).
11.
These changes in shape alter the texture of foods.
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Oxidation of food
Alcohols
1.
Branched-chain alcohols, with up to 8 carbons in their longest chain, can be
named from structural formulae.
2.
Given names of branched-chain alcohols, structural formulae can be drawn and
molecular formulae written.
3.
Identify primary, secondary and tertiary alcohols from structural formula.
4.
Primary alcohols are oxidised, first to aldehydes and then to carboxylic acids.
5.
Secondary alcohols are oxidised to ketones.
6.
When applied to carbon compounds, oxidation results in an increase in the
oxygen to hydrogen ratio.
7.
In the laboratory, hot copper(II) oxide or acidified dichromate(VI) solutions can be
used to oxidise primary and secondary alcohols.
8.
Tertiary alcohols cannot be oxidised.
9.
Oxygen reacts with edible oils giving the food a rancid flavour.
10.
Antioxidants are molecules which will prevent these oxidation reactions taking
place.
11.
Ion-electron equations can be written for the oxidation of many antioxidants.
Carboxylic acids
12.
Branched-chain carboxylic acids, with no more than eight carbon atoms in their
longest chain, can be named from structural formulae.
13.
Given the names of branched-chain carboxylic acids, structural formulae can be
drawn and molecular formulae written.
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Soaps, detergents and emulsions
1.
The alkaline hydrolysis of fats and oils (esters) forms water-soluble ionic salts
called soaps.
2.
The long covalent tail of soap ions is readily soluble in covalent compounds
(hydrophobic); the negatively charged ionic carboxylate head is water soluble
(hydrophilic).
3.
During cleaning using soaps and detergents, the hydrophobic tails dissolve in a
droplet of oil or grease, whilst the hydrophilic heads face out into the surrounding
water.
4.
Agitation of the mixture results in ball-like structure forming with the hydrophobic
tails on the inside and the negative hydrophilic head on the outside.
5.
Repulsion between these negative charges results in an emulsion being formed
and the dirt released.
6.
Detergents are particularly useful in hard water areas.
7.
An emulsion contains small droplets of one liquid dispersed in another liquid.
8.
Emulsions in food are mixtures of oil and water.
9.
To prevent oil and water components separating into layers, a soap-like molecule
known as an emulsifier is added.
10.
Emulsifiers for use in food are commonly made by reacting edible oils with
glycerol to form molecules in which either one or two fatty acid groups are linked
to a glycerol backbone rather than the three normally found in edible oils.
11.
The one or two hydroxyl groups present in these molecules are hydrophilic whilst
the fatty acid chains are hydrophobic.
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Fragrances
1.
Essential oils are concentrated extracts of the volatile, non-water soluble aroma
compounds from plants.
2.
They are widely used in perfumes, cosmetic products,cleaning products and as
flavourings in foods.
3.
Essential oils are mixtures of organic compounds.
4.
Terpenes are key components in most essential oils.
5.
Terpenes are unsaturated compounds formed by joining together isoprene (2methylbuta-1,3-diene) units.
6.
They are components in a wide variety of fruit and floral flavours and aromas.
7.
Terpenes can be oxidised within plants to produce some of the compounds
responsible for the distinctive aroma of spices.
Skin care
1.
Ultraviolet radiation (UV) is a high-energy form of light, present in sunlight.
2.
Exposure to UV light can result in molecules gaining sufficient energy for bonds
to be broken causing sunburn and aging of the skin.
3.
Sun-block products prevent UV light reaching the skin.
4.
When UV light breaks bonds, free radicals are formed.
5.
Free radicals have unpaired electrons and, as a result, are highly reactive.
6.
Free radical chain reactions include the following steps: initiation, propagation
and termination.
7.
Many cosmetic products contain free radical scavengers; molecules which can
react with free radicals to form stable molecules and prevent chain reactions.
8.
Free radical scavengers are also added to food products and to plastics.
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