Chemistry Flashcards
How many elements are in the period table?
118
Who first created the periodic table and when?
Dmitri Mendeleev in 1869
How did Mandeleev arrange the periodic table?
In order of increasing atomic mass and similar properties. He left gaps for the undiscovered elements.
Each horizontal row in the periodic table is called?
A period.
Each vertical column in the period table is called?
A group.
Elements in the same group have?
Similar properties and the same number of valence electrons
Name of group group 1?
Alkali metals
Name of group 2?
Alkaline earth metals
Name of group 7?
Halogens
Name of group 8?
Noble gases
Name of elements in the middle block?
Transition metals
Elements of group 1?
Lithium, Sodium, Potassium, Rubidium, Cesium and Francium
Elements of group 2?
Beryllium, Magnesium, Calcium, Strontium, Barium, Radium
Elements of group 7?
Fluorine, Chlorine, Bromine, Iodine and Astatine
Elements of group 8?
Helium, Neon, Argon, Krypton, Xenon and Radon
Properties of alkali metals?
Soft, shiny metals
Good conductors of heat and electricity
Relatively low melting points
React vigorously with water
Form white products when combined with oxygen
Become more reactive moving down the group
Properties of alkaline earth metals?
Similar properties to alkali metals but slightly less reactive
Properties of the halogens?
Non-metals (apart from astatine a metalloid)
Highly reactive
Become less reactive going down the group
Can displace other less reactive halogens
Chlorine and fluorine are gases
Bromine is a liquid
Iodine is a solid
Properties of noble gases?
Unreactive as they have a full outer shell of electrons
Which side of the periodic table are metals found?
Left
Which side of the period table are non-metals found?
Right
Typical properties of metals?
Shiny solids (Mercury is the only metal that is liquid at room temperature)
They are ductile and malleable
High melting points
Good conductors of heat and electricity
Typical properties of non-metals?
Dull
Brittle
Not malleable or ductile
Poor conductors
Low melting points
What is a metalloid?
Have some properties similar to metals and some similar to non-metals
They are semiconductors as they can be modified to be conductors and insulators
Around how many elements are essential in the human body?
20
Atom definition?
Smallest part of an elements which retains the characteristics of that element.
When did the idea of atoms become a scientific theory?
1808
Dalton’s atomic theory?
1) all matter is made up of atoms
2) all atoms of an element are similar to each other
3) atoms of different elements can combine to form compounds
4) atoms cannot be created or destroyed in chemical reactions
What kind of microscope can be used to see atoms?
Scanning tunnelling microscope
Who discovered the electron and when?
Thomson in 1897
How was the electron discover?
Thomson applied electricity to a glass tube producing cathode rays. The rays were attracted to a positively charged electrode meaning the rays must be negatively charged.
Who proposed the plum pudding model?
Thomson
Explain the plum pudding model?
A random distribution of electrons within a positive cloud.
Who disproved the plum pudding model and when?
Rutherford 1911
How did Rutherford discover the nucleus?
By aiming positively charged particles at a thin sheet of gold. Results showed most carried on straight but occasionally some were deflected meaning atoms must have a small positive centre (nucleus)
Mass and charge of an electron?
1/2000 -1
Mass and charge of a proton
1 +1
Mass and charge of a neutron?
1 0
Atomic mass unit (AMU) definition?
One-twelfth of the mass of carbon 12
What is the atomic number?
The number of protons (also number of electrons in a neutral atom)
What is the mass number?
The number of protons and neutrons
What is an isotope?
An atom of the same element which has a different amount of neutrons
Relative atomic mass (Ar) definition?
The weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of carbon-12 (1 amu)
Definition of relative isotopic mass?
The mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon-12
Definition of relative molecular mass (Mr)?
It is the mean mass of a molecule compared to 1/12th of the mass of an atom of carbon-12
What does a mass spectrometer determine?
Percentage abundance and isotopic mass of each isotope
What is needed to calculate relative atomic mass (Ar)?
Percentage abundance and isotopic mass of each isotope
E.g. Mg-24 at 79% Mg-25 at 10% and Mg-26 at 11%
(24x79)+(25x10)+(26x11)
————————————
100
How to work out Relative molecular mass (Mr)?
Add together all the relative atomic masses of the atoms in the molecule
What is an ion?
An electricity charged atom
What is a negative ion?
Anion
What is a positive ion?
Cation
Metals form ……… ions?
Positive (cations)
Non-Metals form ……… ions?
Negative (anions)
Metals …… electrons
Lose
Non-metals……electrons
Gain
Sulfate
SO4 (2-)
Sulfite
SO3 (2-)
Thiosulfate
S2O3 (2-)
Hydrogen sulfate
HSO4 (-)
Hydrogen carbonate
HCO3 (-)
Carbonate
CO3 (2-)
Nitrate
NO3 (-)
Nitrite
NO2 (-)
Phosphate
PO4 (3-)
Chlorate
ClO3 (-)
Hydroxide
HO (-)
Dichromate
Cr2O7 (2-)
Chromate
CrO4 (2-)
Permangenate
Mn04 (-)
Ammonium
NH4 (+)
Zinc ion
Zn2 (+)
Silver ion
Ag (+)
Copper (II) ion
Cu2 (+)
Iron (II) ion
Fe2 (+)
Iron (III) ion
Fe3 (+)
Name the diatomic molecules
Iodine, bromine, chlorine, fluorine, oxygen, nitrogen and hydrogen
What is an energy level?
Each electron shell
What is an orbital?
An electron sub-shell
How many electrons can each orbital hold?
2
What are the different types of orbitals?
S- P- D- F-
What shape are s-orbitals?
Sphere
What shape are p-orbitals?
Dumbell shaped
How many s-orbitals does each shell have?
1
How many p-orbitals does each shell have?
3
How many d-orbitals are in each shell?
5 (only from shell 3 onwards)
How many f-orbitals does each shell have?
7 (from shell 4 onwards)
How many electrons can energy levels 1-4 contain?
2,8,18,32
Why do electrons in an orbital spin in opposite directions?
To minimise the repulsion between electrons
Ionisation energy definition?
The energy needed to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
What is ionisation energy measured in?
KJ per mole
How to work out empirical formula?
Divide masses by relative atomic mass (to find moles)
Divide each number by the smallest one
These numbers show the ratio required
What is a mole?
The amount of substance that contains 6.022x10(23) particles
What is Avogadro’s number?
6.022x10(23) (the same as the number of particles in each mole of carbon 12)
One mole of any substance is equal to?
It’s relative atomic mass turned into grams
What are moles measured in?
g/mol
How to work out number of moles?
Mass divide by formula mass
How to work out mass?
Moles multiplied by formula mass
How to work out formula mass?
Mass divided by moles
What is percentage composition?
The percentage by mass of each element present in a compound
How to work out percentage composition?
Multiple relative atomic mass by number of atoms
Divide by molecular mass of compound
Multiple by 100
What is molecular formula?
The actual number of atoms of each element in a molecule.
What is empirical formula?
The simplest whole number ratio of atoms or ions of each element in a compound
How to work out molecular formula?
Find empirical formula
Divide actual mass by empirical formula mass
What is a solution?
A mixture of solute and solvent particles
Concentration definition?
Amount of solute in a given amount of solution
Molarity meaning?
An expression of concentration 1M = 1 mole of substance in 1dm(3) of its solution
How to work out concentration?
Number of moles divided by volume
Molar gas volume definition?
The volume per mole of gas molecules at a stated temperature and pressure
What is the volume of one mole of any gas at room temperature and pressure?
24dm(3)
How to convert cm(3) to dm(3)?
Divide by 1000
How to calculate the volume of gas (dm3)?
Number of moles of gas x 24
How to calculate the number of moles of a gas?
Volume of gas (dm3)
——————————
24
Percentage yield definition?
Shows how much product is obtained compared to the maximum possible mass
Atom economy definition?
The percentage of atoms in reactants that form the desired product
Theoretical yield meaning?
The maximum amount of product that could be formed
Why is it difficult to achieve theoretical yield?
Reaction may not have gone to completion
Other side reactions may have taken place
Purification of the product may result in some loss of product
Some product may be left behind in apparatus
Raw materials may not be pure
How to calculate percentage yield?
1) find moles of product
2) find ratio of moles of product to reactant
Actual yield
—————— x 100
Theoretical yield
Limiting reagent meaning?
Any reactant that is not in excess. Meaning the reacting will stop as soon as this is used up.
How to work out the limiting reagent?
Used the balanced equation to see which reactant is used up quicker
How to work out atom economy?
The mass of useful product
————————————x 100
Total mass of all products
Why is it useful to maximise percentage yield and atom economy?
Reduce energy use
Reduce costs
Conserve raw materials
Reduce waste
Reduce pollution
What is a titration used for?
To calculate the concentration of an unknown
How to work out concentration from a titration?
1) calculate the volume, concentration and moles of the known substance
2) use the balance equation to work out mole ratio
3) use the mole ratio to work out the moles of the unknown
4) use the moles and volume of the unknown to finally workout the concentration
What is volumetic analysis?
Finding the concentration of a solution by measuring the volume of a solution that will react with a known volume of standard solution
What is the equation to work out a dilution?
Initial conc. x initial vol. = new conc. x new vol
This is then rearranged as required
Saturated solution definition?
A chemical solution containing the maximum concentration of a solute dissolved in the solvent at a particular temperature. No more solute will dissolve.
Supersaturated solution meaning?
A solution that contains a higher that saturation concentration of solute. Any slight disturbance causes crystallisation of excess solute
Solubility definition?
A chemical property referring to the ability for a given substance to dissolve in a solvent
Precipitate meaning?
Insoluble solid that forms during a chemical reaction and separates out in solution
How to test if chloride ions are present?
First silver nitrate: white precipitate
Then dilute ammonia: precipitate disappears
Then concentrated ammonia: N/A
How to test if bromide ions are present?
First silver nitrate: cream precipitate
Then dilute ammonia: precipitate remains
Then concentrated ammonia: precipitate disappears
How to test if iodide ions present?
First silver nitrate: yellow precipitate
Then dilute ammonia: precipitate remains
Then concentrated ammonia: precipitate remains
How to test for carbonate ions?
Add dilute HCl acid to sample
If effervescence observed carbonate is likely
Transfer gas to limewater, if cloudy CO2 is present
How to test for sulfate ions?
Add barium chloride to sample.
If present white barium sulfate precipitate will form
Types of chemical bonds?
Ionic
Covalent
Dative/co-ordinate covalent
Metallic
Types of physical bonds?
Van der Waals’ forces
Dipole-dipole interaction
Hydrogen bonds
What is an ionic bond?
An electrostatic force of attraction between positive and negative ions, usually between a metal and a non-metal
Structure of ionic compounds?
Each ion attracts oppositely charged ions in all directions. Resulting in a giant ionic lattice structure containing billions of atoms
Properties of ionic bonds in regards to melting/boiling?
Most are solids at room temperature as there is insufficient energy to overcome the strong electrostatic forces of attraction so most have high melting and boiling points
the greater the ionic charge the higher the point
The larger the ion the lower the point as weaker bonds due to being spread over a large surface
Properties of ionic bonds in regards to solubility?
Most soluble in polar solvents such as water. Ionic lattice is broken down and solvent molecules surround the ions. The stronger the lattice the less soluble to compound.
Properties of ionic bonds in regards to electrical conductivity?
Can conduct electricity it only if charged ions can move. So solids cannot but molten/ dissolved compounds can.
What is a covalent bond?
Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms. Occurs in non metals elements, non metal compounds and poly atomic ions
What is a simple covalent molecule?
A few atoms held together by covalent bonds
What are giant covalent structures?
Contain many atoms, each joined to adjacent atoms by covalent bonds. Usually arranged into giant regular lattices
Properties of simple covalent structure in regards to temperature?
Low melting and boiling points as less energy needed to break weak intermolecular forces (not strong covalent bond)
Properties of simple covalent structure in regards to solubility?
They can either be polar or non-polar.
Polar molecules dissolve in polar solvents.
Non-polar molecules dissolve in non-polar solvents
Properties of simple covalent structure in regards to electrical conductivity?
Do not conduct electricity as they do not have any free electrons or an overall electric charge
What is an allotrope?
A different form of the same element in the same state. E.g. graphite and diamond
Properties of giant covalent structure in regards to temperature?
High melting and boiling points due to presence of strong covalent bonds in the structures
Properties of giant covalent structure in regards to electrical conductivity?
Depends if there are any delocalised electrons. E.g. graphite will conduct but diamond will not
Properties of giant covalent structure in regards to solubility?
They are not soluble as covalent bonds in the lattices are too strong to be broken
What is metallic bonding?
Electrostatic interaction between positive metal ions and delocalised electrons. The atoms are ionised and these ions occupy fixed positions in the lattice. Outer shell electrons are delocalised and shared between all atoms within the structure
Properties of metallic bonds in regards to electrical conductivity?
Most conduct electricity in solid and liquid state. The delocalised electrons can move through the structure carrying a charge
Properties of metallic bonding in regards to temperature?
Most metals have high melting and boiling points. Depends upon the strength of metallic bonds within the structure. High temperatures are needed to overcome strong electrostatic attraction between the cations and electrons. The higher the ionic charge of the metal the higher the melting point
Properties of metallic bonds in regards to solubility?
Metals do not dissolve. Any interaction between polar solvents and changed in metallic lattice would lead to reaction rather than dissolving
Properties of metallic bonds in regards to malleability/ductile?
Metals can be hammered and pressed into shape as atoms can roll over each other into new positions without the bonds breaking
Metals can be drawn out into a wire again due to atoms rolling over each other
What is an alloy?
Mixtures containing metals. Not a compound as there can be different ratios of metals. They can modify a metals properties e.g. ions may be different sizes to stop layers moving past each other making it harder
What is a dative/coordinate bond?
Very similar to a covalent bond apart from both electrons involved in the bond are from the same atom.
Intramolecular forces definition?
The forces that hold atoms together within a molecule
Intermolecular forces definition?
Forces that exist between molecules
Three categories of of intermolecular bonding?
Induced dipole-dipole interactions (London/ Van der Waals)
Permanent dipole/dipole interactions
Hydrogen bonding
Which type of force is weaker?
Intermolecular
What is electronegativity?
A measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond. The greater the electronegativity the greater the attraction.
What did Linus Pauling invent in 1932?
The Pauling scale to measure electronegativity of atoms
Electronegativity…….. across a period
Increases
How does atomic radius affect electronegativity?
As the radius increases the bonding pair of electrons becomes further from the nucleus. They are therefore less attracted to the nucleus. So the greater the radius the lower the electronegativity.
How does the number of unshielded protons affect electronegativity?
Full energy levels of electrons shield the electrons in the bond from the increased attraction of the greater nuclear charge, reducing electronegativity
Electronegativity …… down a group?
Decreases
What a non-polar bonds?
The electronegativity in both atoms of the covalent bond is identical so the electrons are equally attracted to them both. This cause symmetrical distribution of electron density around the two atoms.
What is a polar bond?
When a covalent bond is formed by atoms with different electronegativities.
Dipoles meaning?
When there is asymmetrical distribution of electron density because one atom attracts the electrons more strongly this created an imbalance in the charges in the bond.
What symbol is used to show charges between bonds?
Delta positive and delta negative
Polar bonds have a more …….. character?
Ionic
Non-polar bonds have a more ……… character?
Covalent
What is a non-polar molecule?
If the polar bonds are arranged symmetrically, the partial charges cancel each other
What is a polar molecule?
If polar bond are asymmetrically arranged, the partial charges do not cancel each other out
What are van der Waals forces?
Resulting weak forces of attraction between the small charges (temporary dipoles)
How does atomic radius affect van der Waals forces?
As the radius increases the electrons are less attracted to the nucleus so temporary dipoles are easier to induce
How do the points of contact between molecules affect van der Waals forces?
The more points of contact between the molecules the stronger the van der Waals forces
What a permanent dipole-dipole forces?
If molecules contain bonds with a permanent dipole the molecules may align so there is electrostatic attraction between the opposite charges on neighbouring molecules
What is a hydrogen bond?
A special type of permanent dipole-dipole bond interaction found between molecules containing:
An electronegative atom with a lone pair of electrons e.g. oxygen, nitrogen, fluorine
A hydrogen atom attached to the electronegative atom.
The hydrogen bond acts between the hydrogen atom in one molecule and the lone pair of electrons in an electronegative atom of another molecule
Strength of intermolecular forces from highest to lowest?
Hydrogen
Permanent dipole/dipole
Van der Waals
Why is solid water less dense that liquid water?
Hydrogen bonds hold water molecules further apart in an open lattice structure when solid. So the water molecules in ice are further apart than in water
What influences the shape of a molecule?
The total number of electron pairs around the central atom. Lone pairs repel more than bonding pairs.
What is bond length?
The distance between the nuclei of two bonded atoms
What is bond angle?
The angle between two covalent bonds
Basic principles of electron pair repulsion theory?
The electron pairs around the central atom determine the shape of the molecule or ion
The electrons pairs repel electrons each other so they are arranged as far apart as possible
The arrangement of electron pairs minimise repulsion and therefore holds the bonded atoms in a definite shape
Different number of electron pairs result in different shapes
What is a tetrahedral shape molecule?
Four bonded pairs repel each other as far as possible
Bond angle of 109.5
e.g. methane
What is a pyramidal shape molecule?
Contains 3 bonded pairs and one lone pair of electrons. Since the lone pairs repel more strongly than bonded pairs this means the bonded angles are closer together decreasing the bond angle
Bond angle of 107
e.g. ammonia
What is a non-linear molecule?
Two bonded pairs and two lone pairs. The lone pairs repel more strongly creating the V-shape
Bond angle of 104.5
E.g. water
What is a linear shaped molecule?
Molecules that contain 2 bonding regions but not lone pairs
Bond angle 180
E.g. CO2
What is a triagonal planar shape molecule?
Contains 3 bonded pairs and no lone pairs.
Bond angles of 120
E.g. boron trifluoride
What is an octahedral shape molecule?
6 bonded pairs and no lone pairs
Bond angle of 90
E.g. SF6
How to predict molecular shape and angles?
1) work out number of valance electrons of central atom
2) take into account any charges for ions
3) work out the number of covalent bonds made by the central atom
4) work out amount of electron pairs
5) determine the shape
What is a triagonal bipyramidal shape molecule?
5 bonded pairs and no lone pairs
2 x 90
3 x 120
What is endothermic?
Heat taken in, in a chemical reaction. The products have more energy than the reactants.
What is exothermic?
Heat given out, in a chemical reaction. The products have less energy than the reactants.
What is activation energy?
Energy needed to start a reaction. Activation energy used to break bonds so reaction can take place and new bonds can form.
What is bond enthalpy?
The energy it takes to break one mole of a specific bond type in gas form.
How to calculate energy change?
Draw out bonds
Use average bond enthalpy table
Sum of bond enthalpies of bonds broken - sum of bond enthalpies of bonds made.
- figure shows exothermic
+ figures shows endothermic
What is calorimetry?
Doing an experiment in set conditions so you can measure temperature change. Allows you to measure enthalpy change directly. Gives true value rather than approximate.
Mass of surroundings x specific heat capacity of surrounding x change in temperature of surroundings.
Then usually scale up to one mole.
Surroundings usually = water
What is specific heat capacity?
The energy required to raise the temperature of 1g of a substance by 1C.
Units: JK-1g-1
Specific heat capacity of water: 4.18
What is enthalpy of reaction?
Overall energy change at constant pressure, if the conditions are standard conditions we call it the standard enthalpy of reaction
What are standard conditions?
Pressure of 100kPa
Temperature of 298K (25°C)
Concentration of 1M, for reactions with aqueous solutions
The standard state is the physical state of a substance under standard conditions. E.g. H20 is liquid
Standard enthalpy change of reaction definition?
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
Standard enthalpy change of combustion definition?
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.
Since it is only one mole there may be fractions of other substances in the equation.
Standard enthalpy of formation definition?
The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
What is Hess’ law?
If a reaction can take place by more than one route and the initial and final concentrations are the same, the total enthalpy change is the same.
How to use an enthalpy cycle?
Add if arrow going correct way
Subtract if arrow going wrong way
Combustion reactants-products
Formation products-reactants
What is entropy?
A measure of disorder
Solids lower
Gases higher
Reaction rate formula?
Change in concentration (mol dm-3)
——————————————
Time for change to occur (seconds)
For the average time
For more specific use a graph and use a tangent to work out the gradient
What can increase rate of reaction?
Increase temperature
Increase reactant concentration
Increase reactant pressure
Increase surface area e.g. use a powder
Adding a catalyst
Collision theory?
1) particles have to collide
2) have collision energy equal to or greater than the reactions activation energy
3) collide with proper orientation
How does a catalyst affect kinetics?
Increases the rate of reaction without being consumed. The reaction follows a different reaction route, usually with a lower activation energy.
Types of catalyst?
Homogeneous catalyst- reactant and catalyst in same states
Heterogeneous catalysts- reactant and catalyst in different states
Maxwell Boltzmann curve?
Total area under the curve= total number of molecules in the system
Area under the curve and to the right of activation energy= number of molecules with sufficient energetic to react
Main characteristics of maxwell Boltzmann distribution?
No particles have 0 energy
Most particles have intermediate energy
A few particles have high energy
The average energy is not the same as the most probable energy
What is equilibrium?
When reversible reactions reach a balance point, where the amount of reactants and the amount of products formed remains constants.
What is dynamic equilibrium?
The forward and backwards reactions continue at equal rates so the concentrations of reactants and products do not change. On a molecular scale there is constant change, but on the macroscopic scale nothing appears to be happening.
Required conditions:
1) must be a reversible reaction
2) must be in a closed container
What is La Chatelier’s principle?
If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.
Factors that affect the position of equilibrium?
1) pressure
2) concentration
3) temperature
La chatelier’s principle with a change in concentration
If you increase the concentration of the reactants, the equilibrium will shift to the right
If you decreases the concentration of the reactants, the equilibrium will shift to the left
If a product is removed the equilibrium would shift to the right. If the product was continually removed the reaction would eventually turn into an irreversible reaction.
La chatelier’s principle with a change in pressure
Only applies to reactions involving gases
If pressure is increased the equilibrium will move in the direction on the least molecules to try to reduce the pressure.
If pressure is decrease the equilibrium will move in the direction on the most molecules to try to increase the pressure.
If there are the same number of molecules on each side, changing the pressure would have no effect on the position of equilibrium
La chatelier’s principle with a change in temperature
Depends if the forward reaction is exothermic to endothermic
If temperature is increased the equilibrium will try to cool down. The equilibrium will move towards the endothermic reaction.
If temperature is decreased the equilibrium will try to heat up. The equilibrium will move towards the exothermic reaction.
Catalysts and equilibrium
They have no influence on the position of equilibrium but help it to be reached quicker
Industry and la Chateliers principle
Important as can a determine conditions for highest yield but need to consider:
Low temperature and pressure means slow rate of reaction
High temperature and pressure means expensive to run and build suitable equipment
So most use a compromise set of conditions
What is the equilibrium constant?
Kc
Different for every reaction
The size of Kc shows how far a chemical reaction has gone. Indicates the position of equilibrium
What does Kc value tell us?
If >1 the reaction is product favoured so equilibrium lies to the right
If <1 the reaction is reactant favoured so equilibrium lies to the right
When Kc is 10^10 they are regarded as gone to completion, so no longer reversible
When Kc is 10^-10 the reaction is regarded as not taking place
How to work out Kc?
aA + bB cC + dD
Kc = [C]^c [D]^d
——————-
[A]^a [B]^b
So equilibrium concentration of products divided by reactants, raised to the power of their stoichiometry
How to work out Kc questions
Find out the initial amounts, changes and therefore equilibrium moles
Find concentrations, so moles/volume
Use Kc expression
What is organic chemistry?
Concerned with compounds of carbon
What do organic compounds contain?
Carbon, hydrogen and sometimes oxygen and other non-metallic elements
What order are formulas for organic compounds written?
Carbon
Hydrogen
Then any others
Features of carbon?
Can form an infinite number of compounds
Can make up to four covalent bonds (single, double or triple)
Can form covalently linked C-C chains of unlimited length
Forming a variety of branches, linear and cyclic compounds
Name of linear hydrocarbons?
Aliphatic
Name of branched hydrocarbons?
Alicyclic
Name of ring shape hydrocarbons?
Aromatic
How can carbon skeletons vary?
Length
Branching
Double bind positions (if present)
Presence of rings
Homologous series definition?
A group of organic chemical compounds, that have similar structure and properties, the structure only differs by the number of CH2 units in the main carbon chain
Arrangement of bonds carbon can form?
4 single bonds
2 double bonds
2 single bonds and 1 double bond
1 single bond and 1 triple bond
What is the alkane formula?
C(n)H(2n+2)
Alkanes end in the suffix of?
Ane (methane, ethane, propane)
Alkane structure?
Hydrocarbons
Only have single C-C bonds
Saturated (have maximum number of hydrogens)
How are unbranched alkanes named?
The pre-fix of the number of carbons in chains followed by ‘ane’
How are branched alkanes named?
1) identify the longest carbon chain in any direction
2) number the carbon chain (make sure the branched group has the lowest number possible)
3) find the name of of longest chain e.g. octane
4) find the name of the branched group e.g. meth and add ‘yl’
5) find the number of the carbon the branch group is on
6) e.g. 2-methyloctane
7) write in alphabetical order if more than one branch group
Number of carbon chains and names for alkanes?
1) meth
2) eth
3) prop
4) but
5) pent
6) hex
7) hept
8) oct
9) non
10) dec
What is the name of a branch off of a alkane?
Alkyl group
What is a halogenoalkane?
Where one or more hydrogen from an alkane is replaced by a halogen
Name added to alkane with number of branch
What state are the first 4 alkanes at room temperature?
Gas
What state are alkanes 5-8 at room temperature?
Liquid
Alkane properties in terms of boiling point?
The longer the carbon chain the higher the boiling point as the chain increases so does the number of electrons in the molecules so the van der Waals forces are stronger
Straight alkanes have higher boiling points that branches alkanes as the molecules can lie closer together
Alkene structure?
End in ‘ene’
Have at least one C-C double bond
Unsaturated (doesn’t have maximum number of hydrogen atoms)
What is the alkene formula?
H(n)C(2n)
Alkyne structure?
End in ‘yne’
Contain at least one C-C triple bond
Unsaturated
Naming alkenes/alkynes
1) The longest carbon chain must contain the double/triple bond
2) number carbon chain from the end closest to double/triple bond
3) add number to name of the carbon the double bond is on
4) add any groups e.g. methyl
How to test if alkane or alkene?
Use bromine water
Becomes colourless if alkene as bromine reacts with C-C double bond
Stays red/brown if alkane as no double bond to react with
What is hydrogenation?
A reaction in which hydrogen atoms add to each of the carbon atoms in a double bond of an alkene turning it into an alkane
A metal catalyst is used
What is a cycloalkane?
A ring of carbon atoms with two hydrogen atoms attached to each carbon
Formula of C(n)H(2n)
They are saturated
Add cyclo to the name
What is an arene?
Group of aromatic hydrocarbons with a molecular structure containing one or more flat sets of six carbon atoms. Each carbon forms a single covalent bond to the carbons either side and to one hydrogen atom. The final unpaired electron on each carbon is located in the P-orbital that sticks out above and below the plane of the ring. This forms a ring of delocalised electrons.
Unsaturated cyclic hydrocarbons
Benzene is an example
Structure of benzene?
Molecular formula of C6H6
Ring structure
Groups can be added off of benzene
What is the displayed formula?
Shows the arrangement of atoms and the bonds
What are isomers?
Compounds with the same molecular formula but the atoms are arranged differently which can lead to differences in physical and chemical properties
Types of structural isomers?
Chain length isomers
Position isomers
Functional group isomers
Types of stereoisomers?
Geometric isomers
Optical isomers
What are chain length isomers?
Carbon atoms in skeleton arranged differently
What are positional isomers?
Have the same functional groups but attached to different points of the main chain
What are functional group isomers?
Have different functional groups
E.g. alkane, alkene, alcohol, ether
What is a stereoisomer?
Have the same structural formula but different in the arrangement of bonds
What is cis-trans isomerism?
Differ in the arrangement of the groups attached to the carbons in double bonds
What are sigma bonds?
End to end overlap of atomic orbitals
All single bonds
What are Pi bonds?
When the lobe of one atomic orbital overlaps another
Double bonds have a Pi bond as wells as a sigma bond
What is the difference between cis and trans isomers?
If the atoms other than hydrogen are all on the same side of the chain they are cis isomers
If the atoms other than hydrogen are different sides of the chain they are trans isomers
Limitation of cis-trans isomerism?
Hard to figure out which side of which if lots of hydrogens have been substituted for different groups
E.g. one side may have carbon and chlorine and the other fluorine and bromine
What is E-Z isomerism?
Used to identify stereoisomers that cannot be defined at cis or trans
Isomers identified as either E or Z
The higher the atomic number the higher the priority
E corresponds to trans form (opposite sides)
Z corresponds to cis form (same sides)
What is optical isomerism?
Have the same molecular and structural formula but cannot be superimposed as they are mirror images
Can occur when an asymmetric carbon (bonded to four different groups) is present so it forms a chiral centre of the molecule
What is a chiral centre?
When a carbon atoms is bonded to four different groups
How to tell the type of optical isomer?
Can rotate the plane of polarised light.
Clockwise - positive enantiomer (D form)
Anti-clockwise- negative enantiomer (L form)
No effect- racemic/racemate
What is R and S configuration?
Assign priority to all groups from chiral centre by atomic number
View molecule so lowest priority is away from observer
Arrow is drawn around in order of priority groups
If arrow is clockwise it is R form
If arrow is anti-clockwise it is S form
How are halogenoalkanes made?
Free radical substitution
How are halogenoalkenes made?
Electrophilic addition
What are the three key steps of free radical substitution?
1) initiation
2) propagation
3) termination
What is initiation in free radical substitution?
UV light absorbed by halogen molecule to provide energy to break the bond. One electron goes to each halogen and forms two free radicals (homolytic fission)
What is homoloytic fission?
Single bond breaks, one electron to each molecule. Shown by a curly half arrow head. Forms two products that are the same
What is heterolytic fission?
Breaking of bonds. One atoms gains both electrons. So atom is now negatively charged and other is positively charged. Two different products
What is a free radical?
A highly reactive species with a single unpaired electron. Electron is represented by a dot.
What is propagation in free radical substitution?
A halogen radical reacts with a methane molecule. This removed hydrogen from the methane and forms a methyl radical and hydrogen chloride. The methyl radical can then bond with a halogen molecule forming another halogen radical and halogenmethane. During this process the total number of radicals remains the same.
What is termination in free radical substitution?
Total number of free radicals decreases. Free radicals can join together to create stable molecules.
Methyl to halogen
Halogen to halogen
Methyl to methyl
Why is the process of synthesising halogenoalkanes by reacting alkanes with a halogen not cost effective?
Hard to separate the mixture of products formed
What are chlorofluorocarbons?
Halogenoalkane molecules where all the hydrogen atoms have been replaced by fluorine or chlorine.
Why are chlorofluorocarbons bad?
Destroy the ozone layer (O3) due to free radical substitution
How are halogenoalkanes formed from alkanes?
Electrophilic addition. As the double bond is an area of high negative charge making it very reactive.UV light is not needed.
What is an electrophile?
Electron pair acceptor. They accept a pair of electrons to form a covalent bond. They are electron deficient. Represented as E+.
What is a nucleophile?
Electron pair donator. They donate a pair of electrons to form a covalent bond. They can be represented by Nu:
What is the electrophilic addition mechanism?
The double bond in the alkene is electron dense (negatively charged). The electrophile is attracted to this. The electrophile breaks down and undergoes heterolytic fission so both the electrons go to the atom not attaching to the double bond. Finally the atom that accepted the electrons bonds with the other carbon to form a dative covalent bond.
What are alcohols?
Homologous series of organic compounds with the general formula CnH2n+1OH
Names end in ol
Functional group is OH
How to name alcohols?
Name of length of carbon chain with suffix -ol
If there are 3 or more carbons positional isomerism can be displayed
The carbon number the OH is attached to is written before -ol
Properties of alcohols?
Much higher boiling point than alkanes
Boiling point increases as carbon chain length increases
Most are liquid at room temperature
Explaining properties of alcohols?
The electronegative oxygen atom in the hydroxyl group means alcohols are polar so can take part in hydrogen bonding meaning the boiling point will be higher than that of an alkane
Hydrogen bonding also means alcohols can mix with water
How can alcohols be produced?
Hydration of an alkene
add water to alkene in form of steam with a phosphoric acid catalyst. Temperature must be 570K and pressure 60-70 atm
Fermentation
Glucose + yeast —> ethanol + carbon dioxide
Anaerobic conditions
Temperature 25-35c
Yeast dies when ethanol concentration reaches around 15%
Slow process
Advantages of fermentation?
Renewable resources used
Less energy used
Advantages of hydration?
High yield of ethanol
Atom economy of 100%
Fast reaction
Can be done continuously
Types of alcohols?
Primary: have one R group attached to the carbon to which the OH group is attached
Secondary: have two R groups attached to the carbon to which the OH group is attached
Tertiary: have two R groups attached to the carbon to which the OH group is attached
Function group of aldehyde and ketones?
Carbonyl group C=O
Formula of aldehydes and ketones?
CnH2nO
Differences between aldehydes and ketones?
Carbonyl group at the end is an aldehyde. So it has at least one hydrogen attached to it
Carbonyl group in the middle is a ketone so has two carbons attached to it
How to name aldehydes?
Named using carbon chain length and then the suffix -al
Carbons numbered starting with carbonyl group as 1
How to name ketones?
Using length of carbon chain and suffix -one
Carbon number of carbonyl group placed before suffix
Reactivity of the carbonyl group?
Polar
Positive charge on the carbon makes it open to attacked by nucleophiles
Aldehydes and ketones can be reduced, forming alcohol
Aldehydes can be oxidised to carboxylic acids
Properties of aldehydes and ketones?
Small ones are soluble in water due to hydrogen bonding between a lone pair on the oxygen of the carbonyl group and the hydrogen of water
As size increases solubility decreases due to interference in hydrogen bonding by the hydrocarbon tails
Have mid range boiling points as have van der Waals forces AND the polar carbonyl group means dipole-dipole interactions are present
Comparing boiling points of alkanes, ketones & aldehydes, alcohols and carboxylic acids?
Alkanes have the lowest as only van der Waals forces are present
Aldehydes & ketones are higher as they also have dipole-dipole interactions as the carbonyl group is polar
Alcohols are higher still as they also have hydrogen bonding
Carboxylic acids are highest as they have more hydrogen bonds
How are aldehydes produced?
Primary alcohols can be oxidised by an oxidising agent such as an aqueous solution of acidified potassium dichromate which changes colour from orange to green. Water is also produced in the reaction.
How are ketones produced?
Secondary alcohols can be oxidised by an oxidising agent such as an aqueous solution of acidified potassium dichromate. Water is also produced
Why are tertiary alcohols resistant to oxidation?
The lack of hydrogen atoms on the carbon atom to which the hydroxyl group of attached
How to test whether aldehyde or ketone?
Tollens’ reagent:
Sodium hydroxide + aqueous silver nitrate. This forms a brown precipitate of silver nitrate (Ag2O). Aqueous ammonia is added until precipitate dissolves and a solution of the silver amine [Ag(NH3)2]+ is formed.
A silver colour is formed if aldehydes are present
No colour change if ketone
Benedict’s solution:
An alkaline solution containing copper ions.
When heated with an aldehyde the Cu2+ complex ion acts as an oxidising agent and the blue turns to red
No colour change if ketone
Functional group of carboxylic acids?
Carboxyl group (COOH) attached to terminal carbon
How to name carboxylic acids?
Using length of carbon chain and suffix -oic acid
Reactivity of carboxylic acids?
Polar due to presence of two electronegative oxygen atoms and a partially charged carbon and hydrogen atom
Can take part in:
Neutralisation- carboxylic acid loses a proton to from a carboxylate salt
Nucleophillic substitution- partially positive carbon is attacked by nucleophile resulting in substitution of OH group
Esterification- reaction with an alcohol for form an ester
Properties of carboxylic acids?
Solubility depends on side. The smaller the compound the higher the solubility.
Carboxylic acids are higher due to more hydrogen bonds present
How are carboxylic acids formed?
Primary alcohols are reacted with an excess of oxidised agent and refluxed.
Primary alcohol—>aldehyde
—>carboxylic acid
Reflux position is the condenser tube vertical. The condenser tube is continuously surrounded by cold water. As aldehyde is produced it evaporates but the cold water then cools it back to a liquid so it can go back to undergo second oxidisation
Reflux definition: the continuous evaporation and condensation of a volatile substance without loss of any product
Functional group of esters?
-COO-
Carbon double bonded to one oxygen and single bonded to another oxygen
How is an ester formed?
Esterification:
When alcohol is warmed with a carboxylic acid in the presence of an acid catalyst. A water molecule is removed
Concentrated sulfuric acid is often used as the catalyst
The O-H bond of alcohol is broken and water formed with the OH from the carboxylic acid group and the H in the alcohol group
Carboxylic acid + alcohol -> ester + water
Naming esters?
First part from the alcohol used with -yl e.g ethyl
Second part from carboxylic acid used with -anoate e.g. ethanoate
X-yl X-anoate
Hydrolysis of esters?
Chemical reaction using water to break down bonds of a substance
Esters can be hydrolysed by refluxing with either an acid or alkali
With an acid it reverses the ester back to an alcohol and carboxylic acid
With an alkali it hydrolysed to an alcohol and sodium salt of the acid
What is an amine?
Nitrogen containing organic compounds derived from ammonia where one or more of the hydrogen atoms has been replaced by an alkyl or aryl group
Types of amines?
Primary: where one hydrogen from ammonia is substituted with carbon
Secondary: where two hydrogens from ammonia are substituted
Tertiary: where all three hydrogen atoms are substituted
Quaternary: where four carbons are attached to the nitrogen, using ammonia’s lone pair of electrons
Naming amines?
Use the length of the carbon chain and use suffix -amine
E.g. methylamine
If other functional groups are present then the amino- prefix is used
E.g. 2-aminoethanoic acid
Properties of amines?
Solubility: shorted chains are soluble in water as the lone pair of electrons in the nitrogen atom allows them to form hydrogen bonds with water molecules
Larger amines are less soluble as the larger R groups interfere with hydrogen bonds
Boiling points: primary amines have higher boiling points that alkanes as they can form hydrogen bonds .
Secondary amines having slightly lower boiling points as the nitrogen forming the hydrogen bond is in the middle of the chain and this slightly reduces the strength of the dipole
Tertiary amines have even lower boiling points
What is an amide?
Products of reactions between carboxylic acids and amines
An amide and water is produced
Contain functional group CONH
Amino acids contain both amine and carboxylic acid functional groups. They can react together to form an amide link (peptide bond)
Common acids and their formulae?
Hydrochloric acid: HCL Nitric acid: HNO3 Ethanoic acid: CH3COOH Sulfuric acid: H2SO4
Arrhenius model of acids and bases?
Acids dissociate and release H+ ions in an aqueous solution Alkalis dissociate and release OH- ions in an aqueous solution
What is neutralisation?
An acid plus a base equals salt and water H+ + OH- —> H2O For example: NaOH + HCl —> NaCl + H2O
Bronsted-Lowry acid and base model?
Emphasises the role of the proton transfer An acid is a substance that can donate a proton A base is a substance that can accept a proton
What is the hydronium ion?
H3O+ The active ingredient in any acicid solution Usually shortened to H+
What is an conjugate acid-base pair?
It contains two species that the transfer of a proton can interconvert
Amphoteric meaning?
It can act as both an acid and a base Such as water
What do the terms monobasic, dibasic and tribasic refer to?
The total number of hydrogen ions in the acid that can be replaced per molecule
What is a strong acid?
They fully dissociated in water
What is a weak acid?
They only partially dissociate in water
What is a concentrated acid?
A high number of moles of acid in 1dm3 of solution
What is a weak acid?
A low number of moles of acid in 1dm3 of solution
How to calculate pH of a strong acid?
pH = -log10 [H+] The square brackets mean concentration in mol dm-3 of hydrogen ions If diprotic or triprotic, then multiple concentrations by two or three as they will contain more moles of hydrogen per molecule
How to calculate the hydrogen ion concentration from pH?
10^-pH Eg pH 8.75 is 10^-8.75 = 1.78 x 10^-9 mol dm^-3
The equilibrium constant of water?
Kw= [H+][OH-] Since the H and OH in water are equal, it can also be written as: Kw=[H+]^2
How does the pH of water change?
With temperature
Calculating pH from Kw?
Kw = [H+]^2 [H+] = square root of Kw Then calculate pH as normal, -log[H+]
Buffer definition?
An aqueous solution that resists change in pH upon the addition of acid or base
How to prepare a buffer?
Mix a large volume of weak acid/base with its conjugate base/acid
How does a buffer work?
When a strong base is added, the acid present in the buffer neutralises the hydroxide ions When a strong acid is added, the base present in the buffer neutralises the hydronium ions
Standard structure of steroids?
Three cyclohexane rings One cyclopentane ring 17 labelled carbons
Solubility of steroids?
Fat-soluble Derived from fatty acid biosynthesis have a hydrophobic core Some functional groups may impart polarity/ water solubility
What is the simplest steroid?
Gonane Cyclopentanoperhydrophenanthrene
How many chiral centres does gonane have?
6
Where are the chiral centres in gonane?
6 8 9 10 13 14
How many stereoisomers does gonane have?
64 theoretically but only a few occur in nature
What are the two main types of steroid hormones?
Corticosteroids Sex hormones
Where are the corticosteroids made?
Adrenal cortex
Where are the sex steroids made?
Gonads
What are the two types of corticosteroids?
Glucocorticoids Mineralcorticoids
What are the three types of sex steroids?
Androgens Progestogens Estrogens
Where do glucocorticoids bind?
Glucoreceptors
Where do mineralocorticoids bind?
Metal containing receptors
What is the precursor for steroid hormones?
Cholesterol
Effects of steroid hormones on genome pathways?
Binding of hormones to receptors causes configuration changes in the receptor which then has a regulatory effect on the DNA element
Effects of steroid hormones on non-genomic pathways?
Bind to ion channels and GCPRs Can have a direct effect on cell membrane
What type of steroid is dexamethasone?
Glucocorticoid
What can dexamethasone treat?
Rheumatic problems Skin disease Severe allergy Asthma COPD croup Brain swelling Covid-19
What does dexamethasone have such a broad effect?
It affects global receptors It is not specific to one area So it can cause side effects
Chemical structure of dexamethasone?
C22H29FO5 Usual steroid structure but with: - fluorinated at position 9 - hydroxy groups at positions 11, 17 and 21 - methyl group at position 16 - carbonyl (oxo) groups at positions 3 and 20
Dexamethasone mechanism of action?
1) enters the cell 2) binds to an intracellular receptor 3) heat-shock protein is hydrolysed, and releases activated steroid-receptor complex 4) steroid-receptor complex is transported into the nucleus 5) binds to DNA 6) modifies DNA glucocorticoid-responsive elements and transcription factors 7) this alters the transcription of target genes in DNA into mRNA 8) mRNA leaves the nucleus 9) mRNA directs the synthesis of new proteins on cytoplasmic ribosomes 10) these proteins are released from the cell and elicit a biological response
Effects of dexamethasone in low and high doses?
Reduces inflammation. An increase in the production of anti-inflammatory compounds such as annexin-1, SLP1, MOP-1, and nitric oxide synthase
Effects of dexamethasone only with high doses?
Immunosuppressive. Reduces the production of pro-inflammatory compounds, including cytokines, chemokines, adhesion molecules. Also, reduce the production of pro-inflammatory enzymes such as A2 and cyclooxygenase
Actions of anabolic androgenic steroids?
Building things up, such as muscle Regulate several genes associated with virilisation (development of male characteristics)
Why are females more prone to osteoporosis?
The androgenic steroids maintain skeletal integrity in males, whereas, in females, they develop the bones but do not maintain them
Types of synthetic anabolic androgenic steroids?
Testosterone Oxandrolone
Chemical structure of testosterone?
C19H28O2 It contains a ketone functional group at position 3 It contains a hydroxyl group at position 17
Chemical structure of oxandrolone?
C19H30O3
Effects of testosterone vs oxandrolone?
Androgenic : anabolic Testosterone 1:1 Oxandrolone 1:3-13 So oxandrolone has a much greater anabolic effect with less androgenic effects
Side effects of AAS’s?
Physiological issues Testicular shrinkage Heart attack Stroke High BP Male pattern baldness (in males and females) Breast growth in males Breast shrinkage in females
Why are steroids (cholesterol) important for cell membranes?
They can bind with other lipids to produce a liquid ordered membrane. The right levels is crucial.
What are the three types of drug used for the immune system?
Immunoglobulins Immunostimulants Immunosuppressants
What are IVIGs?
Antibodies isolated from patients to give to others Usually in the form of IgM and IgG
Limitations of IVIGs?
Hard to modify
Types of immunostimulants?
Vaccines Interferon (such as Pegasys) Interleukins (aldesleukin)
What are interferons? (as drug treatments)
Cytokines- proteins Have many different effects but usually either down-regulate or activate certain pathways
What are interleukins? (as drug treatments)
Proteins produced in response to an immune response and upregulate the response
What is an example of an interleukin? (as drug treatments)
Aldesleukin IL-2 Used for cancer cells by interfering with growth. It stimulates the immune system By encouraging the growth of killer T cells and other cells that attack cancer
What are immunosuppressants used for?
Reduce inflammation Reduce symptoms of autoimmune diseases Reduce allergic reaction Reduce transplant rejection
Types of immunosuppressants?
Calcineurin inhibitors (cyclosporin, tacrolimus) IL inhibitors (anakinra, tocilizumab) TNFa inhibitors (adalimumab, infliximab) Methotrexate Omalizumab (anti IgE) Azathioprine NSAIDs
How does cyclosporin work?
Forms complexes with cyclophilin to block phosphatase activity of calcineurin. This decreases the production of inflammatory cytokines by T cells.
How do NSAIDs work?
Inhibit cyclooxygenase that makes prostaglandins
How does methotrexate work?
Acts against rapidly dividing cells so can be used for cancer Bone marrow is also rapidly dividing, so it becomes an immunosuppressant
How does carbimazole work?
Inhibits conversion of T4 to T3 to the hormone cannot enter the cell
Why is agranulocytosis associated with carbimazole?
Carbimazole is myelotoxic (toxic to bone marrow), so therefore, a reduction in WBC can occur
What is DHF used for?
to covert to THF to make nucleic acids
Why can we target DHF in bacteria without harming the host?
Humans absorb DHF from the diet but bacteria need to synthesis their own so we can target this enzyme in this process
How do bacteria synthesise DHF?
P-aminobenzoic acid + pteridine —> dihydropteroate —> DHF With the help of the enzyme dihydropteroate synthetase
What is DHF?
Dihydrofolic acid
What is THF?
Tetrahydrofolic acid
When were sulfonamides discovered?
In 1935 Prontosil was used, it was a prodrug that metabolised by breaking a double bond between two nitrogens to sulphanilamide
Mechanism of action of sulfonamides?
Inhibit dihydropteroate synthetase in bacteria The sulfonamide is structurally similar to the natural enzyme-substrate, p-aminobenzoic acid Competitive inhibitors and classed as bacteriostatic
What kind of bonding is the red line?
Hydrogen bonds
What kind of bonding is the blue line?
Van der Waals interactions from benzene ring
What kind of bonding is the yellow line?
ionic bonding
What are the key chemical structures of sulfonamides?
1) aromatic ring 2) sulfonamide group 3) p-substitution only 4) sulfonamide N must be 1° or 2° (either one or two hydrogens present) 5) p-amino group must be 1° (one hydrogen group present) 6) if amino R group is an acetyl group it can act as a prodrug 7) sulfonamide R group is the only variable
Chemical structure of sulfonamides?
how many can sulfonamides be chemically changed?
Changing the R group on the sulfonamide group
How do prodrugs of sulfonamides work?
An amide group lowers the polarity of the sulfonamide and increases hydrophobic character as it cannot ionise but can then be hydrolysed into the active form. This allows the drug to cross the gut wall more easily
How are sulfonamides metabolism?
N-acetylation which increases hydrophobic character which reduces the aqueous solubility and can potentially lead to side effects so we need to try to increase the water solubility of the drug
How can we increase the water solubility of sulfonamides for metabolism?
We can change the R2 group so the sulfonamide N-H bond is more acidic. Converting sulfathiazole to sulfadiazine The pyrimidine ring of the sulfadiazine is more electron-withdrawing therefore making the negative ion formed more stable lowering the pKa of the sulfonamide N-H proton
What is sequential blocking?
Using a combination of drugs that inhibit different enzymes in the same biosynthesis pathway It allows lower, safer dose levels of each drug
General penicillin structure?
General cephalosporin structure?
What is the general structure of a beta-lactam?
Beta= size of ring Lactam= Cyclic amide
Mechanism of action of penicillins?
Inhibit an enzyme called transpeptidase which is needed for cell wall synthesis They are bacteriocidal Gram-positive are more susceptible The penicillin resembles the D-ala-D-ala residue (natural substrate), and the transpeptidase enzyme binds penicillin and catalyses C-N bond fission to give an acetyl enzyme that does not turn over
What is D-ala-D-ala?
Two alanine amino acid residues in a dipeptide structure
Why does penicillin react faster with the transpeptidase enzyme than the natural substrate?
Due to the strain of the four-membered ring A smaller bond angle than usual causes torsional strain meaning the molecules will more readily react to relieve the strain
Essential structure features of penicillin?
1) amide group 2) carboxylic acid/carboxylate 3) B-lactam ring 4) B-lactam ring as a bicyclic 5) variation limited to side chain R
How is penicillin G synthesised?
a standard nucleophilic acyl substitution reaction
Problems with penicillin G?
limited range of activity Not orally active as it’s sensitive to stomach acid Sensitive to beta-lactamases
How to solve the problems of penicillin G?
Increase chemical stability for oral administration Increase resistance to B-lactamases Increase range of activity
How can we increase the acid-stability of penicillin?
Make the side-chain an electron-withdrawing group, drawing the electrons away from the carbonyl oxygen, making it less nucleophilic
How can we stop beta-lactamases?
Add steric Shields (bulky side chains) to stop penicillin from accessing the B-lactamase active site However, if they are too bulky, then it prevents penicillin from binding to the transpeptidase enzyme Give beta-lactamase inhibitors such as clavulanic acid
Essential structural features of cephalosporins?
1) B-lactam ring 2) Carboxylic acid at position 4 is important for binding 3) Bicyclic ring important for increasing ring statin 4) stereochemistry is important
Mechanism of action of vancomycin?
Blocks transglycosidation by providing a binding pocket for the biosynthetic building blocks and binds to the tail of the building blocks peptide chain Forms hydrogen bonds to the target and therefore acts as a receptor for the building block
How does vancomycin resistance occur?
Due to a mutation in a pentapeptide chain of cell wall building blocks where the terminal D-alanine is replaced by D-lactate
Tetracycline structure?
