Chemistry organic chemistry

What are biodegradable plastics?

-Broken down by enzymes

What are photodegradable plastics?

-Broken down by U.V. Light

What is the general formula of alkanes?

CnH2n+2

Are alkanes saturated or unsaturated and why?

-Saturated
-Each carbon atom forms four strong covalent, single, sigma bonds around it

Are alkanes polar or non-polar and why and how does this affect their solubility and reactivity?

-Non-polar - no permanent dipole across the molecule as it is symmetrical so the charges cancel out
-This means that it is insoluble and unreactive because the strong covalent bonds are resistant to attack from other reactive species (nucleophiles and electrophiles) and polar H2O

What is the melting and boiling points of alkanes like? and branching

-They have a varied Tm/Tb
-It increases with Mr
-This is because they have greater surface area therefore more area for contact betwen molecules and therefore greater london forces

-Branching decreases the Tm/Tb
-This is because there is a smaller surface area in contact for the formation of london dispersion forces
-This results in weaker london dispersion forces between the molecules which require less energy to overcome

What is a structura/chain isomer?

-Same molecular formula but a different structural formula

What are the rules with structural isomers?

-Affect carbon chain length
-Alkyl side chain cannot be on the first carbon - the overall carbon chain length must remain the same
-Cyclic alkanes are not structural isomers of alkanes (they a are structural isomers of alkenes)

What are cycloalkanes?

alkanes in which the carbon atoms are arranged in a ring, or cyclic, structure
general formula CnH2n

What is the combustion of an alkane?

-The reaction of the alkane with O2
-Exothermic

When does complete combustion take place?

-When there is excess oxygen available

What are the products of complete combustion?

-CO2 and H2O

How do you balance alkane combustion equations?

1. C
2. H
3. O

How does the energy required/released in complete combustion change with increasing carbon chain length?

-More energy is released to from the products
-More energy is required (to break the bonds in the reactants - activation energy), therefore it is harder to burn

When does incomplete comubstion take place?

-When there is a limited supply of oxygen

What are the products of incomplete combustion?

-CO and H2O

What is the problem with carbon monoxide?

-It is highly toxic
-It binds irreversibally to the haemglobin in your red blood cells forming carboxyhaemglobin
-Less O2 is transported around the body

When is incomplete combustion more likely to take place and what also may be produced?

-With longer chain alkanes (higher activation energy and react with more O2)
-Pure Carbon (soot) may be produced as a product of incomplete combustion

What additional products may be produced from impurities in the fuel (complete/incomplete combustion)?

-SO2 and NOx
-They may be produced as a result of the combustion of Sulphur and Nitrogen impurities in the fuel
-The two products both contribute towards acid rain

What is the effect of and solution to CO2?

-Global warming
-Use more carbon neutral fuel sources such as biofuels

What is the effect of and solution to H2O?

-Global warming
-No solution

What is the effect of and solution to SO2?

-Acid rain:
2SO2 + O2 - 2SO3
SO3 + H2O - H2SO4

-Carry out desulfurisation using CaO/CaCO3
CaO + SO2 - CaSO3 (calcium sulfite)
CaCO3 + SO2 - CaSO3 + CO2 (not as good because CO2 is produced)

What is the effect of and solution to NO?

-Acid rain (HNO3)

-Catalytic converters:
2CO + 2NO - 2CO2 + N2

What is the effect of and solution to CO?

-Smog and health issues

-Catalytic converters:
2NO + 2CO - 2CO2 + N2

What is the effect of and solution to Unburned hydrocarbons?

-Global warming

-Catalytic converters:
C8H18 + 25NO - 12.5N2 + 8CO2 + 9H2O

What is the effect of and solution to Carbon particulates?

-Smog and health issues such as cancer

-Combustion of fuels which release less particulates - this is why petrol is a better environmental alternative to diesel

What is free radical substitution?

A 3 step reaction mechanism when a halogen free radical replaces a hydrogen atom.

What is the first stage of free radical substitution?

-Initiation
-This is where the free radicals are generated
-Cl2 -\> Cl. + Cl.
-U.V light causes the homolytic fission of the Cl-Cl covalent bond generating two Chlorine free radicals
-A free radical is a highly reactive species with an unpaired electron

What is the second stage of free radical substitution?

-Propagation
-This is the alkane hydrogen atoms are substituted for the halogen free radical
-CH4 + Cl. -\> .CH3 + HCl
-.CH3 + Cl2 -\> CH3Cl + Cl.
-The first free radical generated is .CH3 which is a methyl free radical
-The Cl. Is regenerated and is what causes the chain reaction to take place as it reacts with more CH4 producing more of the desired CH3Cl product

What is the third stage of free radical substitution?

-Termination
-This is where the free radicals combine to stop the chain reaction
-Cl. + Cl. -\> Cl2
-Cl. + CH3. -\> CH3Cl (desired product)
-CH3. + CH3. -\> C2H6 (Ethane - alkane twice the size of the original alkane is produced)

What is the overall equation of free radical substitution?

-CH4 + Cl2 -\> CH3Cl + HCl

What are the limitations of free radical substitution?

-Cannot occur in the dark as U.V light is needed to generate the halogen free radicals in the initiation step
-Substitution process is random which means there is no control over which H atom is substituted in larger alkanes (do not know which carbon atom the halgogen free radical will bond to)
-If left to run, multiple substitutions will occur (can have more than one halogen atom on the same alkane)
-As a result of this, multiple products are produced which means that free radical substitution is not a precise process

What is the general formula of alkenes?

-CnH2n
-However, only with 1 C\=C double bond as with more double bonds there will be less H atoms

Are alkenes saturated or unsaturated and why?

-Unsaturated because they have a C\=C double bond
-This means they are open to addition reactions

Are alkenes polar or non-polar and how does this affect their water solubility?

-Non-polar
-Despite the polarity of the C-H bonds, because the molecule is symmetrical, there is non permanent dipole
-This means they are insoluble in water (water is polar)

Are alkenes reactive or unreactive?

-Very reactive
-The Pi bond of the C\=C double contains two p-orbital overlaps which stick out above and below the two nuclei of the bonding atoms
-The Pi bond is the bond that breaks during an addition reaction (as it is weaker)
-This makes the C\=C double an area of high electron density and so it is open to electrophilic attack

Describe the boiling points of alkenes

-Varied
-Their boiling point increases with increasing carbon chain length as their Mr increases
-This means that more electrons are involved in the formation of london dipersion forces
-Therefore there are stronger london dispersion forces which require more energy to overcome

What type of isomerism do alkenes show?

-Geometric isomerism
-They have a non-rotational C\=C double bond

Describe the alkene C\=C double bond in full detail

-Functional group
-Area of high electron density
-Open to electrophilic attack

Describe the Sigma bond in the alkene C\=C double bond

-Formed through the direct overlap between the s orbital of each bonding carbon atom
-Very strong because the overlap is directly between the nuclei of the two bonding atoms so there are strong, electrostatic forces of attraction between the shared pair of negatively charged electrons and both positively charged nuclei of the bonding atoms
-These require lots of energy to overcome

Describe the Pi bond in the alkene C\=C double bond

-Formed through the overlap between the p orbital of each carbon atom
-As the p orbital has a figure of eight shape, there are two overlaps between the two carbon atoms
-However, this is only classified as a single bond
-This bond is much weaker than the sigma bond because they overlap above and below the nuclei of the two bonding atoms
-This means there are weaker electrostatic forces of attraction which require less energy to overcome

What is the alkene shape and bond angle?

-Trigonal planar
-120 degrees

What type of analysis is the test for alkenes and why?

-Qualatative
-Either a yes (alkene) or no (no alkene)

What is Bromine water?

-Br2 dissolved in water

Describe fully how you would test for an alkene?

-Add Br2(aq) dropwise to an organic solvent
-If the test is positive, the Bromine water will turn from orange to colourless (electrophilic addition reaction - Pi bond breaks and Br2 is added to the double bond forming a haloalkane)
-If the test is not positive, no alkene present in the sample, the Bromine water stays orange

What is geometrical isomerism?

-A form of stereoisomerism
-Has groups which occupy different relative positions in space
-Specific to alkenes as they have the non-rotational C\=C double bond

What two things must an alkene have to show geometrical isomerism?

-A C\=C double bond
-Two different groups bonded to each carbon atom in the C\=C double bond

How is geometrical isomerism carried out?

-Focus on the C\=C double bond
-Summarise groups
-Focus on the heaviest "priority" group on each carbon atom
-Look at the positioning of the two priority groups
-The groups are fixed in position due to the non-rotational C\=C double bond
-Therefore the alkenes with different positioning of priority groups will be isomers of each other

Explain the Kahn Inglod prelog system and when Cis-Trans isomerism can be used?

-Look up the atomic numbers of each atom directly bonded to each carbon atom in the C\=C double bond
-For each carbon atom, the atom bonded to it that has the highest atomic number takes priority
-If the two atomic numbers are the same, move to the next atom in the chain and compare until the priority group is identified
-Look at where the two groups are relative to each other
-If they are on the same side then they are Z isomers
-If they are on opposite sides then they are E isomers

-Cis-Trans isomerism can be used when the two priority groups are the same e.g. CH3

-DON'T WRITE IN ANSWER BUT A CHEAT IS THAT THE GROUP WITH THE HIGHEST MR ALWAYS TAKES PRIORITY

What is the general formula of alcohols?

-CnH2n+1OH

Are alcohols saturated or unsturated?

-Saturated
-Each carbon atom forms 4 strong covalent, single sigma bonds

What is the polarity like of alcohols?

-Polar
-There is a permanent dipole across the O-H bond

What is their solubility like in water?

-They are water soluble because the permanent dipole across the O-H bond enables alcohols to interact with water molecules through hydrogen bonding
-However, as their carbon chain length increases, their solubility decreases
-This is because as the size of the non-polar region increases, the polar O-H region becomes less significant

What is their melting and boiling point like?

-They have varied melting and boiling points
-Their melting point is high because they can form hydrogen bonds (due to the permanent dipole across the O-H bond)
-However, as the carbon chain length increases, their Mr increases
-This means that there are more electrons involved in the formation of london dispersion forces
-This results in stronger london dispersion forces which require more energy to overcome

What are the 3 types of alcoholic structures?

-Primary - where the carbon atom bonded to the OH functional group is bonded to 2 hydrogen atoms
-Secondary - where the carbon atom bonded to the OH functional group is bonded to 1 hydrogen atom
-Tertiary - where the carbon atom bonded to the OH funcitonal group is bonded to 0 hydrogen atoms

What is the first way of producing an alchohol?

-Through the nucleophilic substitution of a haloalkane
Haloalkane(alk) + NaOH(aq) — Alcohol + NaX

What is the second way of producing an alcohol?

-Through the hydration of an alkene
-Alkene + H2O — Alcohol
-Temperature \> 100 degrees celcius (steam)
-Dilute phosphoric acid catalyst

What is the third way of producing an alcohol?

-Fermentation
-Renewable source of alcohols (ethanol)
C6H12O6 - 2C2H5OH + 2H2O
-Carried out using the anaerobic respiration of yeast

Compare the methods of hydration and fermentation for producing ethanol

-Hydration is non-renewable as alkanes come from crude oil. Fermentation is renewable as crops can be constantly grown
-Hydration is fast as it is carried out at a high temperature. Fermentation is slow as it is carried out at a low temperature - yeast is a living organism and a low temp prevents the enzymes from denaturing
-Hydration has a high energy input whereas fermantation has a low energy input
-Hydration is a continuous process whereas fermentation is a batch process
-With hydration, you get the pure, ethanol product with a 100 percent atom economy. With fermentation, you get the ethanol in an aqueous solution of yeast and carbon dioxide. This needs to be separated out and there is also a lower atom economy as there are two products produced

-Therefore use hydration for profit and fermentation for the environment

What happens during the combustion of alcohols?

-The alcohols react with excess oxygen to release energy (exothermic reaction with a negative enthalpy change)

How do you balance alcohol combustion equations?

1. Carbons
2. Hydrogens
3. Oxygens

What are the benefits of alcohol combustion?

-Biofuels
-The alcohol can be produced through the fermentation of glucose. This is a renewable source (crops grown) and potentially carbon netural

1. Photosynthesis - 6CO2 + 6H2O - C6H12O6 + 6O2
2. Fermentation - C6H12O6 - 2C2H5OH + 2CO2
3. Combustion - C2H5OH + 3O2 - 2CO2 + 3H2O

6 CO2 absorbed and 6 CO2 released - no net change in the concentration of carbon dioxide in the atmosphere

What are the disadvantages of alcohol combustion?

-Overall, biofuels are not carbon neutral as CO2 is released in the transport of plants/fuel
-Fermentation is a slow, batch process which may not meet the demands of ethanol production
-Land is used for growing crops instead of food production
-Less energy is released when compared to traditional alkane fuels

What can primary alcohols be oxidised to?

-Aldehydes (through partial oxidation)
-Carboxcylic acids (through full oxidation)

What is the formula of a primary alcohol?

RCH2OH

What is the formula of an aldehyde?

RCHO

What is the formula of a carboxcylic acid?

RCOOH

What are the oxidising agents for the oxidation of alcohols?

-Acidified potassium manganate
-H+/KMnO4 or H+/MnO4-
-MnO4- (purple) to Mn2+ (colourless)
-Reduced from oxidation state +VII to +II

-Acidified potassium dichromate
-H+/K2Cr2O7 or H+/Cr2O72-
-Cr2O72- (orange) to 2Cr3+ (green)
-Reduced from oxidation state +VI to +III

What is the equation for the partial oxidation of a primary alcohol?

-RCH2OH + (O) - RCHO + H2O
-Carried out using distillation
-This allows for the aldehyde to be removed from the reaction mixture before it is oxidised any further into a carboxcylic acid
-This is achieved because the aldehyde has the lowest boiling point so can evaporate and condense at the lowest temperature

What is the equation for full oxidation of a primary alcohol?

-RCH2OH + 2(O) - RCOOH + H2O
-Carried out using reflux
-Allows constant heating as the carboxcylic acid does not need to be removed from the reaction mixture as it cannot be oxidised any further

What are secondary alcohols oxidised to?

-Ketones
-Using reflux

What are the oxidising agents for the oxidation of secondary alcohols?

-H+/MnO4-
-H+/Cr2O72-
-Same observations + colour changes as before

What is the equation for the oxidation of secondary alcohols?

-RCHOHR + (O) — RCOR + H2O

What are tertiary alcohols oxidised to?

-They cannot be oxidised
-This is because the structure does not allow for the removal of the H atom from the OH bond as the C-C bond would have to break. The C-C bond has too high of a bond enthalpy to do so

What is the dehydration of an alcohol?

-The removal of H2O from an alcohol to form an alkene (elimination reaction)

What are the conditions of an alcohol dehydration reaction?

-Concentrated H2SO4/Concentrated H3PO4 catalyst and heat over Al2O3(s)

What is the overall reaction of an alcohol dehydration reaction?

Alcohol — Alkene + H2O
-H+ + Al2O3(s)
-With secondary and tertiary as well as asymmetrical alcohols, multiple products can be produced - the double bond can form in more than one position (only for butanol onwards)

How are haloalkanes produced from alcohols?

-Through nucleophilic substitution

How are chloroalkanes produced?

-ROH + PCl5 — RCl + POCl3 + HCl
-This is carried out at room temperature
-HCl (g) is produced which we can observe through the whispy white fumes

How are bromoalkanes produced?

-ROH + HBr — RBr + H2O
-The RBr is produced in situ from 2KBr + conc. H2SO4 — 2HBr + K2SO4
-Therefore, reflux takes place for the reaction to occur and distillation takes place after this to separate out and isolate the haloalkane product

How are iodoalkanes ploduced?

-3ROH + 3PI3 — 3RI + H3PO3
-The PI3 is produced in situ from 2P + 3I2 - 2PI3
-Red phosphorus is used
-Both reflux (for the reaction to occur) and distillation (to separate out and isolate the haloalkane product) take place

What is the general formula of haloalkanes?

-CnH2n+1X
-X is a halogen (Br, I etc..)

Are haloalkanes saturated or unsaturated and why?

-Saturated
-Each carbon atom forms 4 strong covalent, single single sigma bonds

Are haloalkanes polar or non-polar and why?

-There is a permanent dipole across the C-X bond as X is highly electronegative

What reactions do haloalkanes undergo?

-Nucleophilic substitution (to form alcohols)
-Elimination to form alkenes

Are haloalkanes water soluble or not and why?

-Not water soluble
-C-X bond is not polar enough to interact with the polar water molecules (cannot form hydrogen bonds)

What are their melting and boiling points like?

-Higher than corresponding alkanes
-Because they are polar (because of the permanent dipole across the C-X bond) they form permanent-dipole forces between the molecules which require more energy to overcome than london dispersion forces
-As their Mr increases, their boiling point increases because more electrons are involved in the formation of london dispersion forces. This results in stronger london dispersion forces which require more energy to overcome

What are the structures of haloalkanes like?

-Can be primary, secondary of tertiary
-This depends on the position of the Halogen on the carbon chain
-If primary, the Carbon atom bonded to the halogen is bonded to 2 other hydrogen atoms
-If secondary, the Carbon atom bonded to the halogen is bonded to 1 other hydrogen atom (X usually in the middle of the carbon chain)
-If tertiary, the Carbon atom bonded to the halogen is bonded to no otehr hydrogen atoms (involves an alkyl side chain)

Why can't we test for haloalkanes directly?

-We can't test for the presence of the halide ion when it is bonded to the carbon atom

How do we test for haloalkanes?

-Use nucleophilic substitution to release the halide ion which can be tested for

1. Reflux the haloalkane with NaOH(aq) to release the X:- ion
R-X(aq) + NaOH(aq) — R-OH + Na+ + X:-
-Must be in ethanol so that they are miscible

2. Add excess HNO3(aq) to neutralise any excess OH- ions
HNO3 + OH- — NO3- + H2O
-This is important as the next stage is to add AgNO3(aq) to test for the X:- (aq)
-If OH- ions are present, Ag+ + OH- — AgOH(s) which is a brown ppt
-Must use HNO3 otherwise with HCl and H2SO4, Cl- and SO42- ions will form which will form a white ppt with Ag+

3. Add AgNO3(aq) to test for the X:- (aq)
-Ag+ + Cl- — AgCl(s) white ppt
-Ag+ + Br- — AgBr(s) cream ppt
-Ag+ + I- — AgI(s) yellow pp

4. Use conc. and dil. NH3(aq) (ammonia) to distinguish between the ppt's
-AgCl(s) will dissolve in both conc. and dil. NH3(aq)
-AgBr(s) will dissolve in oly dil. NH3(aq)
-AgI(s) will not dissolve
-use dil. NH3(aq) to distinguish between AgCl(s) and AgBr(s)
-use conc. NH3(aq) to distinguish between AgBr(s) and AgI(s)

What is the nucleophilic substitution of a haloalkane?

-Where the halogen atom bonded to a haloalkane is substituted for a nucleophilic group e.g. OH- or CN-

Explain nucleophilic substitution with OH-

-Known as hydrolysis
-R-X (alc) + NaOH(aq) — R-OH + NaX
-Reflux the haloalkane with NaOH(aq) to release the X:- halide ion
-The halolkane (R-X) and NaOH(aq) must be mixed in ethanol to make them miscible

What are the stages of hydrolysis?

-The lone pair on the nucleophilic OH- ion is attracted to the delta positive carbon atom
-This causes the heterolytic fission of the C-X bond
-This generates the nucleophilic X:- halide ion which reacts witht the Na+ ion to form NaX

What is the ease of substitution dependant on?

-The bond enthalpy

-How does the ease of substitution change with different halogens

-As you go down group 7, as the next halogen is bonded to the carbon atom, the bond enthalpy decreases (easier to break)
-The lower the bond enthalpy, the weaker the bond, the more reacitve it is and the easier it is to substitute
-Therefore C-I has the fastest rate of substitution and C-F has the slowest rate of substitution
-Although C-F has the strongest bond polarity as F is the most electronegative, despite the carbon attracting the nucleophile the most as it is the most delta positive, the bond enthalpy is the overriding factor

What is the ease of substitution practical?

-Haloalkane + water — Alcohol + H+ + X:-
-Heat and add AgNO3(aq) as they react
-As soon as the hydrolysis of the haloalkane takes place (nucleophilic substitution with the OH- from the water) the halide ion will be released and will form a coloured ppt with the Ag+ ions from AgNO3(aq)
-AgI will form the fastest (as the C-I bond has the lowest bond enthalpy and is the easiest to substitute) and AgCl wioll form the slowest

Describe the uses of haloalkanes

-Chloroalkanes and chlorofluoroalkanes are used as refrigerants, solvents and repellants

What is the harm of haloalkanes?

-CFC's are damaging the ozone layer in the atmosphere by generating Cl. Free radicals

Describe in full detail the effect of CFC's on ozone?

-CH2FCl — CH2F. + Cl.
-U.V light causese the homolytic fission of the C-Cl bond which generates the Cl. Free radical
-This catalyses the breakdown of ozone (O3) which filters out harmful U.V. Radiation

-Cl. + O3 — ClO. + O2
-ClO. + .O. — Cl. + O2

-The Cl. Is a catalyst because it is regenerated
-Luckily ozone can be regenerated:
O3 + .O. (Reversible arrow) 2O2
-Because this reaction exists in equilibrium, provided that there are no more Cl. Free radicals in the atmosphere, the equilibrium will shift to the left, opposing the increase in O2 and regenerating Ozone

-The solutions to regenerating Ozone are:
1. CFC's have been banned for most uses worlwide
2. HFC's are now being used as an alternative to CFC's as they have no C-Cl bond so cannot generate the Cl. Free radical

Describe the Cahn-Ingold prelog naming system of geometric isomers

-Focus on the C\=C double bond
-Summarise the groups arround it
-Look at the atomic number of each atom bonded directly to each carbon in the C\=C double bond
-This highest atomic number on each side takes priority
-If the two atomic numbers on one side of the double bond are the same, move to the next atom in the chain and compare
-Look at where the priority groups are relative to each other
-If they are on the same side - Z isomer
-If they are on opposite sides - E isomer