Unit 2

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Unit 2 Natures Chemistry
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Oxidation (of food) Aldehydes and Ketones
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Homologous Series (family)

• There is a gradual change in physical properties
  from one member to the next. The most common
  example of this is the increasing melting and
  boiling points as we go up a series. The reason
  for this is the increasing London forces as the
  molecules get larger.
• Members of the same homologous series have
  similar chemical properties and methods of
  preparation.
• The chemical formula increases by CH2 from one
  member to the next up the series.
• Each series has a general formula.
• All members possess the same functional group. It
  is the functional group that gives the series its
  characteristic reactions.

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Alkanols (Alcohols)

• Important characteristics of the alkanols
  homologous series
• The names of all alkanols end in -ol
• The functional group of the alkanols is OH
  (hydroxyl group)
• The first 3 alkanols are polar and therefore are
  ________ in water.
• All alkanols follow the general formula

soluble
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• Three categories of alkanols
• Primary - The carbon attached to the -OH group
  is directly bonded to only one alkyl group. (i.e.
  1 carbon)

white board example
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• Secondary - The carbon attached to the -OH group
  is directly bonded to two alkyl groups. (i.e. 2
  carbons)
• Tertiary - The carbon attached to the -OH group
  is directly bonded to three alkyl groups. (i.e. 3
  carbons)

white board example
white board examples
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Isomers and Naming

• Isomers can result from both chain branching and
  varying the position of the -OH group.
• In naming, the main chain (longest) must contain
  the -OH group, whose position is indicated by a
  number.
• 2. Number the chain to give any branches the
• lowest possible number.
• 3. Name the branches methyl (-CH3), ethyl (-
• C2H5), propyl (-C3H7) etc.

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white board example
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• Example 2 Draw and name the 4 isomers of C4H9OH

white board examples
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Oxidation

• In carbon chemistry, oxidation can mean either
• adding oxygen or removing hydrogen.
• This is often referred to as increasing the
  oxygen
• to hydrogen ratio.
• Full oxidation occurs during combustion
• Combustion of alcohols (in excess oxygen)
• produces carbon dioxide and water.

white board example
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Partial Oxidation Primary and secondary alcohols
will undergo oxidation but tertiary alcohols do
not.
(aldehyde)
No reaction
(ketone)
No reaction
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Chemicals / Reagents used to oxidise alcohols and
their results

• Acidified potassium permanganate solution
  (KMnO4)
• During the reaction the purple permanganate
  (MnO4-) ion is reduced to colourless Mn2 ions.
• Acidified potassium dichromate solution (K2Cr2O7)
  
• During the reaction the orange dichromate ion
  (Cr2O72 ) is reduced to green Cr3 ions.
• Copper (II) oxide and heat
• The black oxide is reduced to reddish copper
  metal during
• the reaction.

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Alkanals (Aldehydes)

• Alkanals are produced via the oxidation of
  primary alcohols
• The names of all alkanals end in -al
• The functional group of the alkanals is CO
  (carbonyl group)
• The carbonyl group is always attached to the end
  carbon
• for the aldehydes.
• The main industrial use for alkanals is in the
  production of
• thermosetting plastics.

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Alkanones (Ketones)

• Alkanones are produced via the oxidation of
  secondary
• alcohols
• The names of all alkanones end in -one
• The functional group of the alkanones is CO
  (carbonyl group)
• This carbonyl group is never attached to the end
  carbon in the
• ketones (and is usually indicated via number.)
• The main industrial use for alkanones is as
  solvents and
• varnishes (propanone is the solvent used for
  nail varnish
• remover)

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How to distinguish between alkanals and alkanones
(aldehydes and ketones)

• As both homologous series have the _______ group
  (in many reactions) they react in similar ways.
• Alkanals and alkanones with the same number of
  carbons are isomers of one another.
• However as the _________ group is found on
  different carbon positions then we can
  distinguish between them using the following
  chemicals

carbonyl
carbonyl
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• Benedicts or Fehlings solution
• Blue solution Orange-red precipitate
• Cu 2 ions reduced to Cu2O i.e. copper (I) oxide
• Tollens reagent i.e. AgNO3(aq) NH3(aq)
• A silver mirror is formed
• Ag ions reduced to Ag atoms
• Acidified potassium dichromate solution
• Orange solution Green solution
• Cr2O7 2- reduced to Cr 3 ions

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Alkanoic Acid (Carboxylic Acids)

• Alkanoic acids (also known as carboxylic acids)
  are produced
• via the oxidation of aldehydes (alkanals)
• The names of all alkanoic acids end in -oic
  acid
• Alkanoic acids are polar and therefore dissolve
  in H2O
• The functional group of the alkanoic acid is
  -COOH (carboxyl
• group)
• This carboxyl group is always attached to the
  end carbon in
• the carboxylic acids. (no numbering needed)
• The O-H part of the carboxyl group provides
  hydrogen
• bonding (see bonding)

Cn H2n1 COOH
General formula
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oxidation
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oxidation
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Antioxidants

• Antioxidants are molecules that play an important
  role in preventing our food from spoiling too
  quickly by stopping oxidation reactions from
  taking place.
• The antioxidant molecules are reducing agents,
  they cause other substances to be reduced while
  being oxidised themselves.
• One of the simplest antioxidants is vitamin C.
• https//www.youtube.com/watch?vQM3lMKoT6U0

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Making Esters

• Esters are compounds formed by a condensation
  reaction between alcohols and carboxylic acids.
• In a condensation reaction two molecules join and
  a small molecule (often water) is removed.

white board example
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Naming Esters The name of an ester indicates the
alkanol and acid which go into making it. The
first part is derived from the alkanol
-anol becomes -yl. (i.e. ethanol becomes
ethyl) The second part is derived from the
alkanoic acid -oic becomes -oate. (i.e.
ethanoic becomes ethanoate)
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• The main difference between fats and oils is
  that
• fats are normally solid at room temperature
• oils are normally liquid at room temperature

From Plants From Animals
Sunflower Oil Beef fat
Olive Oil Cod liver Oil
Vegetable Oil Pork Fat (lard)
Walnut Oil Butter
Why?
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Hint it something to do with melting point

• Oils have a lower melting point than their fat
  counterparts due to the greater amount of
  unsaturation within the (oil) molecules.

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• The absence of a double bond allows the fat
  molecules to be more regularly tuning fork
  shaped and consequently the fat molecules can fit
  into one another.
• If a double bond is present then the oil (and
  some fats) molecules zigzag and the molecule
  chains become distorted and cannot fit into one
  another.
• Molecules which can pack closely together due to
  their regular structure have stronger London
  forces between the molecules and thus higher
  melting points.
• Therefore fats have higher melting points than
  oils and fats are solid at room temperature.

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Fats in the Body

• The main function of fats and oils is to provide
  energy. Fats and oils release about twice the
  amount of energy of carbohydrates.
• Fats/oils release their energy more slowly than
  carbohydrates (think sugar rush!)
• Fats and oils also help provide the body with
  vitamins as vitamins are soluble in fats/oils.
• Margarine manufacturers are required to add some
  of these vitamins to their products to prevent
  certain vitamin deficiency problems.

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The structure of fats and oils

• Fats and oils are actually special forms of
  esters where the alcohol, glycerol
  (propane-1,2,3-triol) has three hydroxyl groups.
• Glycerol is termed a trihydric alcohol.
• Glycerol can therefore make ___
• ester links when reacting with long
  carboxylic acids (fatty acids.)
• 1 glycerol reacts with ____ acids

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• Since glycerol is constant, it is in the acid
  chain that we potentially find the double bond
  if there is a double bond the acid is called an
  alkenoic acid.
• Fatty acids are saturated or unsaturated straight
  chain carboxylic acids with even numbers of C
  atoms ranging from C4 to C24, but mainly C16 to
  C18.
• Bromine can be used to distinguish between
  saturated and unsaturated molecules. (unsaturated
  fats/oils will decolourise bromine.)

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• The above fat/oil molecule is called a
  triglyceride.
• When a fat or oil is formed, the glycerol
  molecule can react with up to three different
  fatty acid molecules.
• Any particular fat is made of a mixture of
  different triglycerides, so no fat or oil is a
  pure triglyceride.

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Turning oils into fats

• It is possible to convert oils into fats. (eg
  Bertolli olive oil spread)
• This takes place via a process known as
  hardening.
• Hardening is an addition reaction (hydrogenation)
  where the unsaturated carbon double bonds are
  converted to saturated single carbon bonds.
• Margarines are made by partial hydrogenation of
  oils using a nickel catalyst. The amount of
  hydrogenation can produce margarines with
  different properties.

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Soaps

• Soaps are made via alkaline hydrolysis of
  fats/oils.
• The alkali used is usually sodium hydroxide or
  potassium hydroxide.
• The fatty acid forms as the sodium or potassium
• salt.
• These salts are then salted out of the reaction
  mixture by adding a great excess of sodium
  chloride and the soap can then be filtered off.

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• Soaps and detergents are known as emulsifiers (or
  emulsifying reagents.) This simply means that
  they allow oils and water to become permanently
  mixed.
• Sodium (or potassium) salts of long chain fatty
  acids have two separate parts in terms of bonding
  a long hydrocarbon chain tail (which is non
  polar) and an charged ionic head (from the
  alkali.)

hydrophobic ('water hating')
hydrophilic ('water liking')
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• When detergent or soap is added to oil and water,
  the tail goes into the oil while the head stays
  in the water.

Oil
Water and detergent
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Amines

• Important characteristics of amines homologous
  series
• The functional group of the amines is NH2. This
  is called the
• amine or amino group.
• The N-H groups provides hydrogen bonding (see
  bonding)
• Small amines are polar and therefore dissolve in
  H2O

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Proteins

• The element of nitrogen is essential in food
  chains and it is found in the form of proteins.
• Proteins are the molecules which make up our
  muscle fibres, hair, nails, skin, enzymes,
  hormones etc.
• Proteins are generally very large molecules which
  are made up from smaller molecules called amino
  acids.
• Protein are naturally occurring polymers.

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• Amino acids (monomers) contain two functional
  groups the amine group (-NH2) and the carboxyl
  group (-COOH)
• As amino acids contain (-COOH) and (-NH2) groups
  then they can react as both an acid or as an
  alkali.
• The number of possible amino acid structures is
  very great, but nature only uses 26 different
  structures.
• Essential amino acids cannot be made by the body
  and must be obtained from our diet.
• Protein molecules normally consist of several
  thousand amino acids condensed together so the
  permutations are endless! (Hence the huge variety
  of protein structures.)

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• Proteins are made via condensation polymerisation
  of amino acids.
• The link formed between the amino acids is called
  a peptide link (also known as an amide link)
• Proteins are also referred to as poly(peptides)
  or poly(amides)

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Type of Proteins

• Proteins in the body perform a vast range of
  jobs. As a result, they exist in a range of sizes
  and shapes.
• These polar peptide links can hydrogen bond with
  each other in the same molecule or with different
  molecules (as shown in above example.)

white board example
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• Fibrous
• Fibrous proteins form the structural materials in
  animal tissues e.g. skin, muscle, hair, nails.
• Globular
• Globular proteins tend to have spiral chains
  folded and twisted round into more compact units.
  E.g. Enzymes, hormones and haemoglobin.

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Enzymes

• Enzymes are biological catalysts.
• Enzymes are said to be specific i.e. each
  enzyme has a particular job/function.
• Enzymes work via the lock and key principle

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• The shapes of the molecules are influenced by the
  presence of hydrogen bonds between the chains.
• Enzymes are most active within certain narrow
  temperature and pH ranges. (optimum)
• The protein structure of the enzyme is
  permanently altered at high temperature or low pH
  conditions as the hydrogen bonds are broken. This
  is called denaturing the protein.
• During denaturing, the enzyme changes shape but
  covalent bonds are not broken.

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Hydrolysis of Protein

• Like all condensation polymers, proteins can be
  hydrolysed back into their amino acid building
  blocks.
• In the lab this can be achieved through refluxing
  the protein with concentrated acid however this
  happens more efficiently in the stomach during
  digestion via enzymes.
• The amino acids produced by the breakdown of
  proteins can be identified by using the technique
  of chromatography.

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known amino acids
Protein Sample being hydrolysed
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Fragrances and Flavours
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Terpenes
Terpenes are key components of the essential
oils of many types of plants and flowers.
Essential oils are a mixture of organic
molecules and are used widely as natural flavour
additives for food, as fragrances in perfumery,
and in medicine and alternative medicines such
as aromatherapy. Essential oils are
concentrated extracts of the volatile, insoluble
(in water) aroma compounds from
plants. Synthetic terpenes have greatly expanded
the variety of aromas used in perfumery and
flavours used in food additives including
creating the distinctive smell of many spices.
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Structure of Terpenes

• Terpenes are unsaturated compounds formed by
  joining together 2 methylbuta-1,3-diene
  (isoprene) units.

white board example
https//www.youtube.com/watch?vsA34OoZBQOE https
//www.youtube.com/watch?vIGCagIgV85g
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Oxidation of Terpenes

• Chemists have found that terpenes can be oxidised
  to
• form new compounds which have different
  properties
• from the original terpene.
• Similarly the reverse (reduction) can occur.
• (just like alcohols, aldehydes and carboxylic
  acids etc)

white board examples
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The Volatility of Molecules

• In chemistry and physics, volatility is the
  tendency of a substance to vaporize.
• Vaporize means to change directly from a solid
  into a vapour without first melting.
• The volatility of a molecule can be predicted
  from its size and the functional groups present.
  (think bonding)
• In general the lower the boiling point, the
  higher the volatility.

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Skin Care ( free radicals)
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UV light

• Ultraviolet (UV) light is a high energy form of
  light and is present in sunlight.
• When molecules become exposed to UV light they
  vibrate and their bonds break. These are known as
  photochemical reactions.
• Sunburn and skin aging are caused by broken
  bonds. Suntan lotion prevents the UV light
  reaching the skin.
• When UV light breaks bonds free radicals are
  produced.

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Free Radicals

• Stable molecules have paired electrons.
• Free radicals are unpaired electrons and are
  therefore very reactive.
• Free radical chain reactions have the following
  steps
• Initiation
• Propagation
• Termination.

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Free Radical Scavengers

• Due to the detrimental effect of free radicals on
  the skin and body, cosmetic companies have
  started adding free radical scavengers to their
  products.
• A free radical scavenger is a molecule which can
  react with free radicals to form stable molecules
  and prevent chain reactions
• Food also contains free radical scavengers in the
  form of ___________.

antioxidants