Flashcards in Organic Chemistry Deck (93)
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1
What is organic chemistry?
The study of carbon and its compounds. Carbon has the ability to bond itself to form chains or ring structures and because of this there are millions of organic chemicals.
The organic chemicals are put into different homologous series.
2
What is a homologous series?
A series of chemicals with the same functional group
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What factors do each member of a homologous series share?
A general formula
Each member of a series differs from the next by CH2
Similar reactivity (reactivity in organic chemistry is decided by the functional group)
Physical properties are affected by chain length
4
Increasing the chain length within a homologous series changes the melting/boiling points. Why?
As the chain length increases, the melting/boiling point increases as there are more van dee waals forces to break down, which requires energy.
5
Naming organic compounds: first 10 root names?
Meth
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
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What can be used as fuel to generate energy? (Combustion)
Alkanes
7
What is complete combustion?
If an alkene burns fully in oxygen, it is complete combustion and the only products are carbon dioxide and water.
8
Balanced equation for complete combustion of methane?
CH4 + 2O2 -------> CO2 + 2H2O
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What happens if an Alkane burns in a limited supply of oxygen?
Incomplete combustion occurs and a range of additional carbon products can be formed. Amongst them is carbon monoxide or just carbon (soot)
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Advantages of fossil fuels?
They are available in various forms so the type of fuel can be matched with its use. E.g. Coal and natural gas are used in power stations
Always available at all times. E.g. Solar and wind have limited availability
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Disadvantages of using fossil fuels?
They are non renewable. It takes millions of years to form them, but they are used quicker than they are formed.
Combustion of fossil fuels produces carbon dioxide. This results in the greenhouse effect which causes sea levels to rise and changes to crop suitability
As many contain sulfur, which produces sulfur dioxide and sulfur if acid.
H2O (l) + SO2 (g) ------> H2SO3 (aq)
H2SO3 (aq) + 1/2O2 (G) ----> H2SO4 (Aq)
These react to form nitric acid, HNO3. Sulfuric and nitric acids are present in acid rain, this can cause serious damage to buildings especially those containing calcium carbonate.
Form carbon monoxide, which is toxic since it combines with haemoglobin in the blood so that it is then not available to carry oxygen around the body
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What is halogenation? And what does the reaction proceed by?
The reaction between an organic compound and a halogen. The reaction proceeds by a mechanism known as free radical substitution, which is a chain reaction
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What is a radical?
Radicals are species with an unpaired electron. They are very reactive.
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What is the condition required for initiation? (Free radical substitution)
UV light.
15
What is homolytic fission?
The splitting of a covalent bond evenly. Each atom receives one electron
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What are the three stages of free radical substitution?
Initiation
Propagation
Termination
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What Important observation can be noted from the propagation reaction?
The Br/Cl/F etc. radical is acting as a catalyst
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What are the problems with termination?
Other products form. A mixture of products is produced
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What is the downside to reactivity? (Free radical substitution)
The reactivity of free radicals makes using them difficult and controlling them near impossible.
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Mixtures are always produced in reactions that involve radicals. How can the desired product be isolated?
Fractional distillation
21
What are halogenalkanes? (Haloalkanes)
Alkanes with halogen groups attached and they are named accordingly.
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General formula of haloalkanes?
CnH2n+1X Where x is a halogen
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Functional group of haloalkanes?
|
|
---- ----------- C ---------- X
|
|
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What decides the reactivity of the haloalkanes family?
The polarity of the carbon-halogen bond is an important consideration of its functional group as it is this bond that decides the reactivity of the family.
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What is the relationship between polarity and size of the halogen?
The polarity of he c-x bond decreases as the halogen gets larger. This is due to the halogens becoming less electronegative
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What is bond enthalpy also known as?
Bond strength
27
Explain bond enthalpy
If a bond is broken a certain amount of energy must be supplied to break the bond. The energy required is the bond enthalpy and it is used as a measure of the strength of a bond.
28
For carbon-halogen bonds, does the bond enthalpy increase or decrease as we move down group 7?
The enthalpy of the c-x bond decreases down the group as the bond becomes less polar. So less energy is needed to break the bond of larger halogens
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What tells us how a haloalkane reacts?
The bond polarity
30
Explain reactivity (bond enthalpy)
The bond polarity of the haloalkanes tells how a haloalkane reacts but it is the bond enthalpy that is the more important factor in deciding reactivity. The bond enthalpy tells us that as we move down group 7 the carbon-halogen bond becomes weaker. The order of reactivity is therefore:
Iodo
Bromo
Chloro
Fluoro
The bond polarity of the haloalkanes means that carbon will have slightly positive charge. A positive charge will attract negative charges. The carbon is therefore open to attack by a species called a nucleophile
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What are nucleophiles?
Electron pair donors. That means that they can donate a pair of electrons to an atom that is deficient in electrons. Nucleophiles will have a lone pair of electrons and may have a negative charge.
In the haloalkanes, the polarity of the carbon-halogen bond means that the carbon atom is electron deficient and will be attacked by a nucleophile. The nucleophile will be added to the carbon and the hydrogen will leave. The overall reaction is called nucleophilic substitution
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What is the general term given to a nucleophile?
Nu
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What are the conditions required for nucleophilic substitution?
NAOH (aqueous)
Reflux
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What happens in elimination reactions?
A small group of atoms break away from a larger molecule and are never replaced
35
Conditions of elimination reaction?
Anhydrous, no water is present
36
Explain the properties of the haloalkane structured that enable them to be used as solvents.
They contain a polar section due to the carbon halogen bond and also contain non polar section due to the presence of the alkyl chain. Therefore they can mix with a variety of polar and non polar organic substances
37
One advantage of haloalkanes as solvents?
They are non flammable
38
Example of when halogenalkanes are used as solvents?
In dry cleaning clothes
39
Explain in detail what makes halogenalkanes such good refrigerants?
They have permanent dipole- permanent dipole attractions which means their boiling points are close to room temperature. That means they are liquids that are easily evaporated or gases that are really easily liquified at room temperature. They are good at refrigerants since the heat needed to change the liquid to the gas is removed from the fridge to cool its contents
40
It has been proven that CFCs damage the ozone layer. Explain why this is bad
If there is damage to the ozone layer, UV Rays will be able to reach the earths surface and cause skin cancer
41
What is meant by the phrase CFC?
Halogenalkanes containing both chlorine and fluorine
42
Which family of chemicals are now being used instead of CFCs? Explain why they are better for the environment.
HFCs as they do not form radicals when exposed to uv radiation
43
How do you test for halogenalkanes?
As halogenalkanes are halogens substituted onto an Alkane carbon chain, lab tests focus on the individual halogen attached. In order to test for the presence of the halogen it must first be removed.
1.excess aqueous NaOH is added,
2. Addition of dilute nitric acid.
The nitric acid is added because it removes 2-impurities. The main impurity is a carbon iron (CO3) which would form a white precipitate with silver nitrate of silver carbonate (Ag2CO3)
3. Addition of aqueous silver nitrate
4. Confirmation using ammonia
Aqueous silver ions combine with free aqueous halide ions in precipitation reaction. The precipitate for each halide is a distinctive colour. Ammonia is used to confirm which halide is present.
44
What colour precipitate is formed when you add Ag+ (aq) to each halogen?
Chlorine - white ppt
Bromine - cream ppt
Iodine - pale yellow ppt
45
What happens to each halogen in the haloalkane when NH3 (aq) is added to the precipitate formed?
Chlorine - dissolve in dilute NH3 (aq)
Bromine - dissolves in concentrated NH3 (aq)
Iodine - remains insoluble
46
What is an alkene?
Unsaturated hydrocarbons. They contain at least one carbon-carbon double bond.
47
Fully describe the bonding present in the double carbon-carbon covalent bond of an alkene
The first bond within the c=c is made from end-on-overlap of an atomic orbital. This type of bond is a sigma bond. Sigma bonds are normal, strong covalent bonds.
From the carbon, The remaining e- in a p-orbital, There is a side on overlap of p-orbitals. His type of bond is a pi bond. Pi bonds are covalent condos buttery weaker than sigma bonds. Their shape makes them less stable
48
Alkanes are the most reactive of all homologous series. Why are they so reactive?
Alkanes have an electron rich area between the two carbon atoms of the double bond. This means they undergo addition reactions.
49
What are electrophiles?
Electron pair donors
50
Explain electrophilic addition
The electrophiles are attracted to the double bond, which opens up. When the double bond opens, new atoms are added to the alkene. Alkanes react by electrophilic addition because chemicals add across the double bond
51
Example of electrophiles?
Polar molecules - the d+ region of a polar bond will be attracted to a strong source of electrons.
52
Example of a common addition reaction of Alkanes?
Bromine (test for Alkenes)
A common lab test for Alkenes is the addition of bromine water. The bromine water will decolourise from brown to colourless in the presence of Alkenes
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How to test for Alkenes?
Addition of bromine water
Bromine water will decolourise from brown to colourless in the presence of Alkenes
54
What is heterolytic fission?
When a bond breaks unevenly and one atom receives both electrons
55
How to test for Alkenes? (Not bromine water)
Potassium manganate (VII) is purple and in the presence of an alkene will decolourise.
56
What will hydrogen halides do?
React with Alkenes. They add across the Double bond in electrophilic addition reactions.
57
Explain unsymmetrical Alkenes
Most Alkenes are unsymmetrical. They have a different number of carbon atoms and substituents on each side of their double bonds. When these Alkenes undergo electrophilic addition reactions two possible products are possible. Which one is the major product depends upon the carbocation intermediates; the most stable carbocation will lead to the most stable product.
58
Explain carbocation stability
The stability of a carbocation depends on the groups attached to the carbon bearing the positive charge. Alkyl groups are Alkanes that have a hydrogen atom removed. The more alkyl groups attached to the positive carbon, the more stable the carbocation. The stability arises due to the fact that alkyls group donates electrons toward the positive carbon. This helps to negate the deficiency of electrons
59
Which of the carbocations are more stable?
Tertiary carbocations are more stable as they pull electrons towards itself from 3 different carbons (inductive effect)
60
What other reactions, apart from electrophilic addition, do Alkenes undergo?
Hydrogenation
Polymerisation
61
Explain hydrogenation
Hydrogenation is the addition of hydrogen. When hydrogen reacts with an alkene it adds across the double bond. A metal catalyst, usually nickel is essential. This process is widely used in the food industry to convert oils into solids or semi solids such as margarine.
62
What catalyst is used in hydrogenation?
Raney nickel
63
Explain polymerisation
The Alkenes are the parent family of chemicals of the entire plastics industry. Alkenes can react with each other by adding across the double bond. The entire product molecule is then linked by single bonds. The process is known as addition polymerisation, the Alkenes are called monomers and the products are polymers
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What are the problems with plastics?
Addition polymers are non-biodegradable because they have an inert carbon chain running through them. This means the plastics do not break down over time and the amount of waste increases. However, if the plastics are burnt, toxic fumes are produces which are harmful, to overcome this problem we try to recycle the plastics so they are melted down and re used. The plastics have to be sorted before they are melted
65
What are stereoisomers?
They have the same structural formula but the atoms are arranged differently in space.
66
What are geometrical isomers?
Isomers with the same structural formula but the bonds are arranged differently in space. They only occur around carbon-carbon double bonds
67
When can the E-Z notation be used?
If every group around the carbon-carbon double bond is different. It is based on the atomic number. If the two groups with the highest atomic number are on the same side, the prefix Z is used.
If they are on opposite sides, E is used.
68
General molecular formula for alcohols?
CnH2n+1OH
69
What does the number of alkyl groups attached to the carbon of the functional group tell us?
Whether an alcohol is primary, secondary or tertiary. If there is one alkyl group, the alcohol is primary , two secondary, three tertiary
70
What are the two main processes that make alcohols?
Fermentation
Catalytic hydration
71
Fermentation:
(Explain and equation)
Fermentation uses an aqueous solution of a sugar and yeast to produce ethanol. The yeast produces an enzyme that converts sugars (such as glucose) into alcohols.
30-40 Deg C
C6H12O6 (aq) --------------------> 2C2H5OH (aq) + 2CO2
Yeast
72
Explain catalytic hydration of ethane + equation
Ethene comes from crude oil, which is a non renewable source. It can be converted into ethanol by hydration.
The reaction between ethene and steam to form ethanol is reversible:
C2H4 (g) + H2O (g) -----------> CH3CH2OH (l)
73
Conditions for reaction of catalytic hydration of ethene?
300 degrees Celsius
60-70 atmospheres
Phosphoric acid catalyst
74
Why is fermentation a better option going forward?
The process utilises renewable resources. The ethanol itself is considered carbon neutral as the CO2 generated in its production is used up in the growing of the sugar canes
75
Explain dehydration
Dehydration is the removal of water
Dehydration of an alcohol produces an alkene. Concentrated sulfuric acid is used as a catalyst. The reaction is an elimination as a small molecule is removed
76
Explain oxidation
Alcohols undergo oxidation reactions. The most common oxidising agent is potassium dichromate (K2Cr2O7). Acidified with dilute sulfuric acid. The potassium dichromate changes from Orange to green during the reaction, the reaction products are different depending on whether the alcohol is primary, secondary or tertiary
77
Explain the oxidation products
The actual product produced when alcohols are oxidised depends on the type of alcohol used (p,s or t). Primary alcohols oxidise to aldehydes, which are then oxidised to carboxylate acids. Secondary alcohols oxidise to ketones, tertiary alcohols do not oxidise
78
What two testing solutions are added to test for ketones or aldehydes?
Fehlings solution (a copper complex)
Tollens reagent ( a silver complex)
79
What are the observations with aldehydes and ketones when fehlings solution is added?
Aldehyde: blue --> brick red
Ketone: stays blue
80
What are the observations with ketones and aldehydes when tollens reagent is added?
Aldehyde : colourless --> silver mirror. Grey precipitate
Ketones: remains colourless
81
What are carboxylate acids?
Highly oxidised homologous series
E.g. Methanoic acid
82
What are the two of carboxylic acids most important reactions?
When they act as acids
Reaction with alcohols to form esters
83
Is propanoic acid a polar or non polar molecule?
It is polar, it has a permanent unequal distribution of electrons that it is driven by differences in electro negativity. The strongest type of IMF between molecules are hydrogen bonds
84
What does the term weak acid mean?
An acid that is only partially ionised in aqueous solution
85
Acid + base =?
Salt + water
86
What observations are made in reactions of carboxylic acids with bases?
No visible change
With an indicator, a colour change will be observed
Observe a temperature change
87
Observations of reaction of carboxylic acid with carbonates and hydro carbonates?
Effervescence
Gas can be shown to be carbon dioxide by testing it with lime water
88
What are esters?
Sweet smelling homologous series produced by the reaction of carboxylic acids and alcohols
89
What is the reaction called which reacts carboxylic acids with alcohols?
Esterification
90
What does Esterification use as a catalyst?
Concentrated sulfuric acid
91
Is Esterification reversible?
Yes
92
Describe process of refluxing
Heat is applied until the solvent (and any other volatiles in the reaction mixture) boil gently
They are vaporised and move up to the condenser where they are condensed and drip back into the reaction flask
At the end of the reaction, the mixture is cooled and then further steps are required to isolate the desired product from the reaction mixture
Anti bumping granules are often added to control the heating. Too much heat could cause degradation of reactants or products
93
