Download Demonstrate understanding of the properties of organic compounds

Demonstrate understanding of the
properties of organic compounds
A.S. 91391
Chemistry 3.5
5 External credits
Naming Organic Molecules
• Alkane, alkene, alkyne
• Mepbphho?
• label side chains so numbers are as small as possible and
alphabetically
• Label multiple bonds with the lowest number
• More than one side chain di, tri etc
3-ethyl-2-methylpentane 3,3-diethylhexane
cyclopropane
2,3-dimethylbut-2-ene
Chemical reactions of Alkanes
• Combustion – write balanced equations for the complete and
incomplete combustion of propane
• C3H8 + 5O2
3CO2 + 4H2O
• C3H8 + 2O2
3C + 4H2O
• Substitution – write the equation for the reaction of Chlorine
with Ethane in the presence of U.V. light
uv
CH3CH3 + Cl2 → CH3CH2Cl + HCl
light
• This reaction will continue slowly until the Ethane is fully
saturated with Cl atoms
• Name the haloalkane and suggest a test to prove that the gas
produced is acidic
• chloroethane, damp blue litmus turns pink
Chemical reactions of alkenes
• Combustion – same as alkanes
• Addition – the c=c double bond breaks and small molecules
add themselves e.g.
Pt at room
temp or Ni at
• Hydrogenation
150oC
CH2=CH-CH2-CH3 + H-H
CH3-CH2-CH2-CH3
• Halogenation (chlorination or Bromination)
CH3-CH=CH-CH3 + Br-Br
CH3-CHBr-CHBr-CH3
• Distinguishing test for alkenes
• Hydration
330oC Or
CH2=CH-CH2-CH3 + H-OH dil.H2SO4 at CH2OH-CH2-CH2-CH3
60atm
• This is an unsymmetrical alkene so Markovnikoffs rule applies
• name both the major and minor product formed in the above
reaction
Chemical reactions of alkenes (cont)
• Hydrohalogenation – adding hydrogen halides
•
•
•
•
•
CH2=CH-CH2-CH3 + H-Cl
CH3-CHCl-CH2-CH3
This is an unsymmetrical alkene so Markovnikoffs rule applies
name both the major and minor product formed in the above
reaction
Addition polymerisation High temp,
and
CH2=CH2 + CH2=CH2 pressure
-CH2-CH2-CH2-CH2catalyst
Oxidation – forms diols (purple to colourless, without acid it
will go brown)
H+ CH OH-CHOH-CH -CH
CH2=CH-CH2-CH3 + MnO4
2
2
3
Chemical reactions of Alkynes
• Addition reactions occur with halogens and hydrogen to
produce alkenes and then alkanes.
Hydrogenation
Ni/1500C
• H-C=C-H + H2
CH2=CH2
Ni/1500C CH -CH
• CH2=CH2 +H2
3
3
Halogenation
Br2
• H-C=C-H + Br2
CHBr=CHBr
Br2
• CHBr=CHBr +Br2
CHBr2-CHBr2
• Name the products
• 1,2 – dibromoethene and 1,1,2,2 - tetrabromoethane
Physical properties of hydrocarbons
• Both butane and methylpropane are gas at
room temperature but which has the
lower BP and MP and why?
• More weak intermolecular attractions
(temporary dipoles) can occur in straight
chain molecules, so butane will remain as
a liquid for longer.
• MP and BP will both increase with
increasing molecular mass (C5 to 16 are
oils >16 wax)
• As there are no free moving charged
particles they don’t conduct
• As they are non-polar they are insoluble in
water.
Constitutional (structural) isomers
• Compounds with the same molecular
formula but different arrangement of
atoms.
• Draw and name the structural isomers of
C4H10 and C4H8
• But-1-ene, but-2-ene, methylpropene,
cyclobutane
• Alcohols can form structural isomers but
they also form optical isomers
Optical Isomers (enantiomers)
• Have atoms connected in the same order
but with a different 3D arrangement
• Involve molecules with an asymmetric
Carbon atom (bonded to 4 different
groups)
• Identify the asymmetric carbon with an
asterisk
• Chiral molecules exist in 2 forms which are
mirror images (laterally inverted)
• Chemical and physical properties are
similar but each will rotate the plane of
polarised light in different directions.
• 50:50 mixture of enantiomers shows no
optical activity
Geometric Isomers
• Double bonds cannot rotate
about the C atoms
• Each carbon in the double bond
must have 2 different groups
attached
• Draw the formula for But-2-ene
H
C =C
CH3
CH3
H
Trans but-2-ene
CH3
H
C =C
CH3
H
Cis but-2-ene
•If the Carbon chain is on
different sides of the
multiple bond it is trans
otherwise cis
•What about but-1-ene?
Physical properties of haloalkanes
• The halogen–carbon bond is
polar but not enough to make
the haloalkanes soluble in
water (no H- bonds)
• MP and BP is dependent on
temporary dipoles which
increase with mass
• I > Br > Cl > F
• There are no free moving
charged particles so
haloalkanes are nonconductors
Chemical reactions of haloalkanes
• The carbon-halogen bond is polar so the slight positive charge
on the carbon can attract molecules or ions with a lone pair of
electrons.
• Substitution – the halogen can be replaced by aqueous OH- to
produce alcohol or by NH2 to produce amines
This reaction needs high pressure and conc. ammonia dissolved
in ethanol
Chemical reactions of haloalkanes (cont)
• Elimination reactions involve the removal of a hydrogen and
halogen atom to form a hydrogen halide and an alkene.
Heat and conc. KOH (alc)
• CH3CH2CH2I
CH3CHCH2 + HI
• Consider the elimination reaction of 2-Bromobutane, what
products are formed?
• But-2-ene and HBr and … But-1-ene
• Markovnikov’s rule “The rich get richer, poor get poorer”
• Hydrogen is eliminated from the C with least H’s already
• But-2-ene is the major product and But-1-ene the minor
Alcohols
• Name alcohols with the suffix –ol
• ensure the –OH is part of the parent
chain and that it is given the lowest
number
Propan-1,2,3-triol (glycerol)
Basis of soap and nitroglycerine
• Dihydroxy: two OH groups per molecule.
• Trihydroxy: three OH groups per molecule.
Ethan-1,2 –diol
(ethylene glycol)
antifreeze
Classifying Alcohols
Alcohols are classified as:
primary (1o)
• (C atom with –OH is bonded
to 1 other C)
secondary (2o)
• (C atom with –OH is bonded
to 2 other C)
tertiary (3o)
• (C atom with –OH is bonded
to 3 other C)
Name the alcohols and draw ALL the
isomers of the secondary alcohol
• The same classification is true for haloalkanes and amines,
where the N is attached to 1,2 or 3 C
Physical properties of alcohols
• Alcohol molecules with <4 C are soluble
in water due to the hydrogen bonding
between the hydroxyl group and water
molecules
• When there are >4 Carbons the non-polar
region dominates and the molecule is
soluble in non-polar solvents due to
permanent and temporary dipole
attractions
• Alcohols are used in industry (perfumes)
as they can dissolve polar and non-polar
substances
• MP and BP increase with mass and are
higher than the corresponding alkane
• Alcohols do not conduct as the hydroxyl
group does not readily donate protons,
the molecule has no free moving charged
particles
Chemical reactions of alcohols
• Alcohols burn in air to produce water and carbon dioxide.
• More likely than alkane to undergo complete combustion
• Primary alcohols are oxidised (using Cr2O72-/H+ or
MnO4-/H+) to form aldehydes and then carboxylic acids
• A mixture of all of these is usually formed and can be separated
via fractional distillation
Chemical reactions of alcohols (cont)
• Secondary alcohols are oxidised to form ketones
Ketone bodies are three
water-soluble molecules that
are produced by the liver
from fatty acids during
periods when insulin is low.
“Fruity breath” is often a sign
of diabetes.
• Substitution (chlorination)
Reacting with thionyl chloride (SOCl2) produces a liquid
haloalkane plus HCl and SO2 (both gas)
Tertiary alcohol shaken with conc. HCl
also forms a layer of haloalkane
Chemical reactions of alcohols (cont)
• Elimination (dehydration)
• Water can be removed using heat and a catalyst to
produce an alkene
Conc
H2SO4
or
Al2O3
at
1700C
• The same reaction occurs with unsymmetrical
secondary alcohols but Markovnikov’s rule applies.
• Write equations for the reaction of butan-2-ol and
name the major and minor products
• But-2-ene (major), but-1-ene (minor)
Chemical reactions of alcohol (cont)
• Ethanol can be produced via fermentation of
glucose by Yeast
• Ethanol can also be made by reacting haloalkanes
with aqueous NaOH or KOH
• Alcohols also react with carboxylic acids to form
esters – more later.
Amines
•
•
•
•
Amines are derived from ammonia
If the N is attached to one carbon chain it is a primary amine
Secondary amines have 2 alkyl groups and tertiary have 3
Name the parent chain, position of the amino group and if
there are other groups attached to the N then prefix with ‘N’
rather than the number eg. N-ethyl, N-methylpropylamine
Physical properties of Amines
• Higher mp and bp than
similar molecular mass
alkane due to…
• Hydrogen bonding and
permanent and temporary
dipoles.
• Methanamine and
ethanamine are gases,
propanamine is liquid
• Low mass amines are
soluble in water due to the
hydrogen bonding between
the amine group and water
Chemical reactions of Amines
Methylammonium ion
•
•
•
•
•
•
•
Amines are weak bases because of the non-bonding electrons
CH3NH2 (aq) + H2O
CH3NH3+ + OHIndicator colours?
Name?
Neutralisation reaction with acids to form salts
CH3CH2NH2 (aq) + HCl (aq)
CH3CH2NH3+ + ClName?
CH3CH2NH3+ + ClCH3CH2NH3+ClWhat is the name of the product formed when propylamine
reacts with methanoic acid?
• Propylammonium methanoate
• Why does lemon juice reduce the fishy smell?
Chemical reactions of Amines
• Substitution reactions occur between primary amines
and haloalkanes to form secondary amines.
• CH3CH2NH2 (aq) + CH3F
CH3CH2NHCH3 + HF
• HF will react with the ethanamine to form a salt
called…. Ethylammonium fluoride
• Overall reaction
• 2CH3CH2NH2 + CH3F CH3CH2NHCH3 + CH3CH2NH3+F-
Aldehydes
• Alcohol dehydrogenated
• The C=O (carbonyl group)
is at the end of the
carbon chain
• Name the parent chain
from the aldehyde group
with the suffix –al
Methanal
(formaldehyde)
2-ethyl,2-methylpentanal
pentanal
3,3-dimethylbutanal
Ketones
• The C=O (carbonyl group) is
NOT at the end of the
carbon chain
• Name the parent chain
with the suffix –one
• Use a number to identify
the position of the carbonyl
group and side groups
• Why is there no ethanone?
Propanone(acetone)
4-methylpentan-2-one
2,4-dimethylpentan-3-one
Physical properties of aldehydes
• The carbonyl group is polar
so the intermolecular
bonding is fairly strong.
• MP and BP increase with
mass
• Oxygen in the carbonyl
group has lone pairs of
electrons which can form
hydrogen bonds with water,
therefore short chain (<3C)
aldehydes are soluble
• Most aldehydes are
pungent smelling liquids at
room temp
H
Physical properties of ketones
• The carbonyl group is polar
so the intermolecular
bonding is fairly strong.
• MP and BP increase with
mass
• Oxygen in the carbonyl
group has lone pairs of
electrons which can form
hydrogen bonds with water,
therefore short chain (<4C)
ketones are soluble
• Most ketones are sweet
smelling liquids at room
temp
Aldehydes and ketones are soluble
in non-polar solvents. Propanone
(acetone) is an industrial solvent.
Preparation of aldehydes and ketones
• Oxidation of a primary
alcohol produces an
aldehyde and secondary
alcohols produce ketones
• Alcohol and aqueous
oxidant is added, dropwise
to prevent further oxidation
to a carboxylic acid
• Reflux can be used to
ensure all the alcohol is
oxidised, volatile material
condenses back into the
flask
Testing for aldehydes
• Weak oxidants like
– Tollens’ reagent
(colourless to silver/black ppt)
– Fehlings solution
(blue solution to red/orange ppt)
– Benedicts solution
(blue solution to red/orange ppt)
• can oxidise aldehydes but not
alcohols or ketones
Reduction of aldehydes and ketones
• Sodium borohydride
NaBH4 (dissolved in
water, methanol or
ethanol) can be used to
increase the hydrogen
content of both
aldehydes and ketones
producing primary and
secondary alcohols
respectively.
Carboxylic acids
• Name the parent chain with the suffix –oic acid
• C in the –COOH group is always C1
Propanoic acid
2,3-dichlorobutanoic acid
2-chloropropanoic acid
4-amino, 2,2-dichlorobutanoic acid
Physical properties of carboxylic acids
• Colourless liquids or white solids at room temp
• Methanoic and ethanoic acid are soluble due to hydrogen
bonding attractions
• Solubility decreases with increasing chain length.
• Short chain molecules tend to be “smelly”
• Higher m.p and b.p than equivalent hydrocarbons and
alcohols due to stronger intermolecular bonding and the
formation of dimers
Chemical reactions of Carboxylic Acids
• Behave like weak inorganic acids as they partially ionise in
water
Ethanoate and
hydronium ions
•
•
•
•
•
What would the pH be? How would indicators change?
Why do solutions of carboxylic acid conduct electricity?
Acid + base
salt + water
Acid + metal
salt + hydrogen
Acid + carbonate
salt + water + carbon dioxide
Chemical reactions of carboxylic acids
(cont)
• Acid chlorides (alkanoyl chlorides) are formed
when the –OH group from the carboxylic acid
is replaced by a Cl atom
• Name the parent chain from the –COCl group
with the suffix –oyl chloride
Butanoyl chloride
2-ethyl-3,3-dimethylbutanoyl chloride
Physical properties of acid chlorides
• Pungent fuming liquids at room temp
• Short chain molecules are soluble in water due to
hydrogen bonding attractions
• Solubility decreases with increasing chain length.
• lower m.p and b.p than the equivalent alcohols and
carboxylic acids as there are no hydrogen bonds
• Formed from carboxylic acids via a substitution reaction
using a reagent like thionyl chloride (SOCl2)
Chemical reactivity of acid chlorides
• Due to the highly positive C atom nucleophilic substitution reactions
occur with reactants with a free pair of non bonding electrons.
Ammonia reacts to form a primary amide and
ammonium chloride. Write the reaction for
ethanoyl chloride and ammonia
Amines react to form secondary amides and a
chloride salt
• Ethanoyl chloride + ethanamine
N-ethylethanamide +
ethylammonium chloride
Chemical reactivity of acid chlorides
(cont)
• Violent exothermic reaction with water to
form a carboxylic acid and HCl, therefore
solutions of acid chloride are very acidic
• A steamy gas is seen, this is HCl (g) dissolving
in moist air to form hydrochloric acid
Chemical reactivity of acid chlorides
(cont)
• Acid chlorides react with alcohol to produce esters
and hydrogen chloride
• This is a fast and efficient way to produce esters but
needs to be completed in a fume hood because of
the HCl production
Naming Esters
• Split the molecule at the C-O bond
• Name the alcohol part with –yl ending
• Name the carboxylic acid part with –oate
ending
Methyl propanoate
CH3CH2C
Your turn
Ethyl methanoate
HC
Production of esters (esterification)
• alcohol + carboxylic acid
• Methanol + methanoic acid
Sulfuric
acid
catalyst
ester + water
methyl methanoate + water
• CH3OH + COOH
HCOOCH3 + H2O
• Elimination reaction
• Heat under reflux conditions, neutralise excess acid, add
MgSO4 as a drying agent and separate layers
Acid acts as a catalyst
and dehydrating agent
what effect does it
have on the
equilibrium and rate of
reaction?
Physical properties of esters
• Esters are colourless
liquids
• Sweet/ fruity smelling
• Not soluble (except
methyl methanoate)
• Lower b.p. and m.p. than
constituent alcohol or
carboxylic acid because
esters cannot form
hydrogen bonds
Hydrolysis of esters
• Under acidic conditions the ester reacts with
water and is split into the carboxylic acid and
alcohol again (reverse of esterification)
• methyl methanoate + water
HCOOCH3 + H2O
methanol + methanoic acid
CH3OH +
COOH
• Under basic conditions the products are
alcohol and carboxylate ion
Triglycerides
CH2
OH
CH
OH
CH2
OH
Glycerol
+ 3 Fatty Acids = Triglyceride
O
C
Long hydrocarbon chain
Nonpolar tail
OH
Carboxyl end
Polar head
Triglycerides
Triglycerides are esters
O
CH2
O
C
CH2(CH2)13CH3
O
Glycerol
backbone
CH
O
C
CH2(CH2)13CH3
O
CH2
O
C
Fatty acids
( palmitic acid)
CH2(CH2)13CH3
Ester bonds
Saponification
Soap is made by heating fats with NaOH (Hydrolysis reaction).
The sodium salt of the carboxylic acid is called soap, the other
product is glycerol.
Reactions of esters (cont)
• Hydrolysis of esters using ammonia is slow
and produces an alcohol and amide
• The unbonded electron pair on ammonia is
attracted to the positive C in the ester bond
Amides
• Name the parent chain with the suffix –amide
• If there are other groups attached to the N then prefix with
‘N’ rather than the number
• If the N is attached to one carbon chain it is a primary amide
• Secondary amides have 2 alkyl groups
Physical properties of amides
• White, odourless solids with high m.p. and
b.p. due to hydrogen bonding between free
electrons on the O and the amide group.
(dimer formation)
• Low molecular mass amides are soluble in
water others are soluble in non-polar solvents
Preparation of amides
1. Ammonia reacts with carboxylic acids to form an ammonium salt
which can be heated to form a primary amide and water. Write
the reaction for ethanoic acid and ammonia
heat
• Ethanoic acid + ammonia
ammonium ethanoate
ethanamide + water
2. Esters react with conc. ammonia to form an alcohol and an amide
3. Acid chlorides react with ammonia to form an amide and
hydrogen chloride
Remember: secondary amides can be made by reacting acid
chlorides with primary amines
Chemical reactivity of amides
• Remember: Amines were basic and soluble in
acid
• Amides are neutral and insoluble in HCl
• Hydrolysis in acid
• Hydrolysis in base
Addition polymerisation
H
H
C
C
H
H
H
High
C
temp and
H pressure
C
H
H
Ethene
Ethene
H
H
H
H
C
C
C
C
H
H
H
H
Poly(e)thene
General formula for addition polymerisation:
n
C
C
C
C
e.g.
teflon
coating
or PVC
n
• n = the number of monomer units.
• n ranges from 2,500 to 25,000
e.g. Polypropylene
15000
H
CH3
C
C
H
H
H
CH3
C
C
H
H
15000
Condensation polymerisation
• Polyesters, polyamides and proteins are all forms of
condensation polymer
• Formed via repeating esterification reactions which involve
monomers with 2 functional groups per molecule.
• Water is removed as the ester bond is formed between
molecules
Polyamides and polypeptides
• A peptide link is the same
as an amide link
• Polyamides are molecules
with repeating amide links
• Polypeptides are based on
repeating amino acid units
• Nylon is strong, elastic
and resistant to abrasion
(tights, ropes)
Amino acids
• Molecules with an amino and
carboxylic acid group
• Carboxylic acid C is always C1 and
glycine
the amino group is attached to C2
• C2 in amino acids (except Alanine) Amino ethanoic acid
have 4 different groups bonded
(asymmetric) therefore they are
chiral molecules
• Living things can only use 1 form
of the optical isomer
Alanine
2-aminopropanoic acid
Properties of amino acids
• The proton donated by the carboxyl group is gained by the
amine group so amino acids exist as zwitterions
• This means amino acids are very soluble in water
• The strong ionic bonding between zwitterions makes them
solids with high m.p. and b.p. at room temperature
proteins
• 2 amino acids can be joined
via a condensation reaction
to form a dipeptide.
• Many amino acids form a
polypeptide (primary
structure)
• Hydrogen bonding occurs so
the polypeptide chain forms
a 3D secondary structure
• Further folding creates a
tertiary structure