Organic Chemistry Chemical Reactions

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  • Created by: Lotto65
  • Created on: 04-03-18 10:43
Does benzene decolorise bromine water?
No
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Give an example of the catalyst used for when chlorine reacts with benzene
Aluminium chloride
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What is formed when benzene reacts with chlorine?
Chlorobenzene (C6H5Cl)
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What would the product be called in iodine reacted with benzene?
Iodobenzene
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What is the reaction called when a halogen reacts with benzene?
Halogen substitution
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What is required for complete combustion of alkanes to occur?
Excess air/oxygen
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What is produced from complete combustion?
Carbon dioxide and water
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What are products of incomplete combustion (of alkanes)?
Carbon monoxide, carbon (soot) and water
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What are the actual products when ethane is combusted?
Carbon dioxide, carbon monoxide and carbon and water
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What sort of flame is produced in incomplete combustion?
Smoky flame
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What is required for alkanes to react with halogens?
UV light
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What type of reaction is the reaction between an alkane and a halogen?
(Free radical) substitution reaction
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What is mono-substitution?
Replacement of one hydrogen atom with one (halogen) atom
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Is the reaction between alkanes and a halogen easy to control?
No
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What sort of products are formed from the reaction between an alkane and a halogen?
A mixture of products - some involving multiple substitutions
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Why can a mixture of products be formed from free radical substitution?
The products could react again and be substituted again
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What is UV light used for in free radical substitution?
To break apart the diatomic halogen molecules into separate halogen atoms
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Why is the halogen bond broken not C-H in free radical substitution?
Halogen bonds are weaker than C-H bonds so they are broken
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What is a free radical?
Species (atoms or groups of atoms) with an unpaired electron
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Why are free radicals very reactive?
Due to their unpaired electron
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How many electrons go to each halogen when the bond breaks in free radical substitution?
One
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What is homolytic fission?
When molecules are symmetrical so two identical species are created e.g. chlorine molecule splitting into two chlorine free radicals. Same products are formed
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How do you show the movement of one electron in a diagram?
Fish hook arrow (half arrow)
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What is the first atom chlorine free radicals react with? Why?
Hydrogen in the alkane because they contain one electron so it will pair up the unpaired electron
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What is produced when a chlorine free radical reacts with an alkane?
Hydrochloric acid and an alkyl free radical (take off a hydrogen and add a free radical symbol)
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What does the alkyl free radical react with in free radical substitution?
Diatomic halogen molecule
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What is formed when an alkyl free radical reacts with a halogen diatomic molecule?
Halogenoalkane and halogen free radical
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How is free radical substitution a chain reaction?
One initial event (homolytic fission) triggered a large number of subsequent events as free radicals are produced and reused
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What does each cycle of free radical substitution generate?
A free radical
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What is the concentration of free radicals in a free radical substitution reaction mixture? So what is the chance of them colliding?
Low. Little chance of collisions
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Name the three termination reactions that can occur in free radical substitution?
Chlorine free radicals react together; Methyl free radicals react together; Chlorine and methyl free radical react together
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What is formed when two methane free radicals react together?
Ethane
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What reacts together for the actual substitution to occur in free radical substitution?
Alkyl free radical and DIATOMIC halogen molecule
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How are other products formed in free radical substitution?
Chlorine free radical reacting with halogenoalkanes
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Where is the free radical sign placed with a halogen?
At the end of the atom
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Where is the free radical sign placed with an alkane/ compound?
At the beginning of the molecule
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What do you have to consider with free radical substitution in longer alkanes?
Halogen could be on different carbon atoms
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What type of reactions do alkenes undergo?
Addition reactions
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At what temperature do halogens react with alkenes?
Room temperature
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Alkene + halogen molecule -->
Dihalogenoalkane
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What speed does iodine react with an alkene at room temperature?
Very slow
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What can be an intermediate in the reaction between an alkene and a halogen molecule?
Carbocation
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What is the name of the reaction between an alkene and hydrogen?
Hydrogenation
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What temperature does hydrogenation of alkenes occur?
150 degrees celcius
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What is the catalyst used for hydrogenation of alkenes?
Finely divided nickel catalyst
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What is formed from the hydrogenation of alkenes?
Alkanes
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What is formed when an alkene reacts with a hydrogen halide?
Halogenoalkane
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How does the reaction of an alkene with a hydrogen halide take place?
Bubble the alkene through a concentrated solution of the hydrogen halide at 100 degrees celcius
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Which hydrogen halide out of hydrogen chloride or hydrogen iodide reacts the fastest with alkenes?
Hydrogen iodide
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What catalyst is often used when hydrogen chloride reacts with an alkene?
Aluminium chloride
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What is formed when an alkene reacts with water?
Alcohol
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Give two requirements for the reaction between water and an alkene?
Concentrated sulfuric acid and heat
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How is the reaction between water and an alkene often done in a laboratory?
Pass the alkene through a concentrated solution of sulfuric acid at room temperature and then warm the product with water
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What is the (industrial) name for the reaction between water and an alkene?
Catalytic hydration
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How is the reaction between water and ethene done in industry?
React ethene (from crude oil) with steam at 300 degrees celcius and 6000kPa pressure with a phosphoric acid catalyst
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Why is ethanol industrially produced?
Fuel or solvent
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How else can ethanol be produced? Where will the major energy input come from?
Fermentation of a raw material (sugar) which can be done at lower temperatures. Energy input will come from distillation of ethanol
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Oils are what type of fat?
Unsaturated
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Where do oils come from?
Vegetable sources
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Where do fats come from?
Animal sources
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What type of fat are animal fats?
Saturated fats
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Hydrogenation of alkenes is used in the production of...
Margarine
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What gives oils a low melting point?
Cis double bonds in the unsaturated fats
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What does partial hydrogenation do literally and to the margarine?
Converts some of the double bonds to single bonds; Increases margarine's melting point to be a solid at room temperature
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What is bad about partially hydrogenated vegetable oils?
Produces trans fats thought to be bad for heath (cardiovascular disease)
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What type of fat is supposed to be good for health?
Saturated fats (mono)
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What is the reaction between an alkene and bromine water?
Alkene + water + bromine --> bromoalcohol + Hydrogen bromide (note: hydrogen and bromine will be on separate carbon atoms)
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How do you go from a monomer to a polymer in addition polymerisation reactions?
Break the double bond
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Where does addition polymerisation occur?
Alkenes become alkane polymers
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What is required for the polymerisation reaction of ethene?
200 degrees celcius; 2000atm; oxygen or peroxide catalyst
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Polyvinylchloride =
Polychloroethene
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Give two oxidising agents used to oxidise primary and secondary alcohols
ACIDIFIED potassium dichromate (VI); ACIDIFIED potassium manganate (VII)
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What are the chemical formulae for the two oxidising agents used to oxidise primary and secondary alcohols?
K2Cr2O7/H+; KMnO4/H+
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What are primary alcohols oxidised into? Using which oxidising agent?
Primary alcohols --> Aldehydes (partial oxidation) --> Carboxylic acids (complete oxidation). Acidified potassium dichromate and heat for both parts
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What does the acidified potassium dichromate become in oxidation reactions? What are the colour changes?
Cr2O7 2- (orange) --> 2Cr3+ (green)
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What is the colour change when potassium manganate reacts in oxidation reactions?
MnO4- (purple) --> Mn2+ (colourless)
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A primary alcohol heated under reflux produces...
Carboxylic acid
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A primary alcohol distilled produces...
Aldehyde
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Why do aldehydes have a lower boiling point that alcohols?
No hydrogen bonding so distillation works
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What is formed when a secondary alcohol is oxidised with an oxidising agent?
Ketones and water
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Does anything but the functional group change in organic reactions?
No
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What is required in esterification?
Concentrated sulfuric acid and heat
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Is esterification a reversible or irreversible reaction?
Reversible
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In esterification, what is lost from the carboxylic acid molecule?
OH
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In esterification, what is lost from the alcohol?
H
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Give two other ways esterification reactions can be described?
Condensation or nucleophilic substitution reactions
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Which organic compounds undergo nucleophilic substitution?
Halogenoalkanes
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What is required for a halogenoalkane to be nucleophilically substituted into an alcohol?
Sodium hydroxide and heat
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What is another word for the reaction between a halogenoalkane and sodium hydroxide?
Hydrolysis
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Halogenoalkane + ammonia -->
Amine + hydrogen halide
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What is required for a halogenoalkane to react with ammonia?
Concentrated ammonia and heat in a sealed tube
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What is required for halogenoalkanes to form nitriles?
Potassium cyanide; methanol and heat under reflux
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Why is the reaction between potassium cyanide and a halogenoalkane useful?
A way of increasing the carbon chain
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Why are halogenoalkanes more reactive than alkanes?
Presence of halogen makes a polar bond to attract a nucleophile to the carbon. Carbon-halogen bond is weaker than C-H or C-C and Cl- is stable in many solvents
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What makes a nucleophile attracted to a C-Br bond?
Polar bond so carbon is delta + and Br is delta -
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What type of bond is formed between a nucleophile and the carbon atom?
Coordinate covalent bond
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What do curly arrows represent?
A lone pair of electrons
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What type of fission occurs when the C-Br bond breaks in SN2 nucleophilic substitution?
Heterolytic fission
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Where is the transition state on an energy level profile?
Highest point
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What does SN2 mean?
Substitution nucleophilic bimolecular so two molecules are involved in a certain step (rate-determining)
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What happens to the configuration of the molecule in SN2 nucleophilic substitution?
It gets inverted as the OH- enters (opposite side to the halogen)
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What is molecularity?
The number of molecules or ion in a particular step in a mechanism
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Why is SN2 nucleophilic substitution stereospecific?
Arrangement of groups around a chiral centre in the reactant determines the stereochemistry of the product
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At what temperature can tertiary halogenoalkanes be nucleophilically substituted?
Room temperature
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If you double the concentration of either halogenoalkane or NaOH in SN2 nucleophilic substitution, what happens to the rate?
It will double
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What is the rate-determining step of SN1 nucleophilic substitution?
Breaking the C-Br bond to form a carbocation
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Why does the rate equation for SN1 nucleophilic substitution not contain the nucleophile?
Nucleophile being added is not in the rate-determining step
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Is SN1 nucleophilic substitution stereospecific?Why/ Why not?
No because the molecule is planar so the nucleophile can attack from either direction and the stereochemistry of the final product is random
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Which halogen out of chlorine, bromine and iodine has the greatest rate of nucleophilic substitution in SN1 and SN2 mechanisms? Why?
Iodine because the C-I bond is easiest to break due to larger atomic mass. DO NOT THINK ABOUT ELECTRONEGATIVITY
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Is the rate of an SN1 reaction affected by the nucleophile? Why/ why not?
No because the nucleophile is not added until after the rate-determining step
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What sort of nucleophiles will make SN2 reactions faster? Why?
Ions because a higher negative charge increases the attraction to the carbon (delta +) atom
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Which nucleophilic substitution mechanism do secondary halogenoalkanes undergo?
A mixture of the two and depends on specific conditions in the reaction
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Why is SN2 mechanism favourable for primary halogenoalkanes?
The methyl groups surrounding the central carbon atom make it very hard for an OH- ion to enter. If it did enter, there would be 5 bonds on the carbon atom making it very unstable and have a high activation energy
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Why is SN1 mechanism favourable for tertiary halogenoalkanes?
Methyl groups have an electron-releasing effect to stabilise the molecule and spread out charge. The more methyl groups, the greater spread of charge so the more stable and more likely to be formed
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What is faster when reacting with NaOH: SN1 or SN2?
SN1
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What is a protic solvent?
A polar solvent with a hydrogen bonded to N or O so can hydrogen bond
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What is an aprotic solvent?
A polar solvent that does not have a hydrogen bonded to N or O and cannot hydrogen bond. They are not proton donors
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Give examples of aprotic solvents
Propanone, dimethyl sulfoxide
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What sort of ions can protic solvents solvate?
Positive and negative ions
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What sort of ions can aprotic solvents solvate?
Positive ions
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How are negative ions solvated?
Interaction with hydrogen attached to O or N by hydrogen bonding
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Which nucleophilical substitution mechanism is good for protic solvents?
SN1
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Which nucleophilic substitution mechanism is good for aprotic solvents?
SN2
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Why is a protic solvent better for SN1?
A positive and negative ion are formed in the rate-determining step of SN1 and a protic solvent can solvate both
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Why is an aprotic solvent better for SN2?
An aprotic solvent does not surround the nucleophile and solvate it to prevent it reaching the halogenoalkane
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Why is a non-polar solvent better for SN2 nucleophilic substitution?
Allows the nucleophile to attack the halogenoalkane and means the negative charge is more spread out in the transition state instead, so the nucleophile is less stable and the activation energy is lowered
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What must the solvent be able to do in nucleophilic substitution reactions?
Dissolve the halogenoalkane and the nucleophile
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What are the reactants in electrophilic addition?
Alkene and hydrogen bromide
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What is the Lewis acid and what is the Lewis base in electrophilic additon?
Lewis acid is hydrogen bromide and alkene in second stage; Lewis base is alkene and halide ion
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What is Markovnikov's rule?
When H-X adds across the double bond in an alkene, the hydrogen attaches to the carbon with the most hydrogen atoms already
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Why does Markovnikov's rule work?
Secondary carbocations are more stable than primary ones due to the electron releasing effect where the charge is spread out more. The more alkyl groups, the more stability and the more likely the ion will be formed
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With interhalogen compounds like Br-Cl, which one is attached to the carbon with more hydrogens in electrophilic addition?
The one with less electronegativity (bromine) behaves like hydrogen
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Why does the electrophilic addition of an alkene with a halogen need a non-polar solvent?
When the halogen molecule comes close to the double bond, it becomes polarised and electrons are repelled to give delta + to the halogen closest but if it was solvated, it could not react
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What is required for benzene to produce nitrobenzene?
Benzene, concentrated sulfuric acid, concentrated nitric acid, heat under reflux at 60 degrees celcius
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What does nitrobenzene look like?
Benzene without one hydrogen and with NO2 attached instead
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What is the first step in the nitration of benzene?
Concentrated nitric acid reacts with concentrated sulfuric acid to produce the nitronium ion (NO2+)
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What is the reaction between concentrated nitric and sulfuric acid?
HNO3 + 2H2SO4 --> NO2+ + H3O+ + 2HSO4-
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In the nitration of benzene, what is the Lewis acid and base?
Lewis acid is the NO2+ nitronium ion and the Lewis base is the benzene
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Why does the delocalised system in benzene get a positive charge during nitration?
To bond to the nitronium ion, the delocalised system lost 2 electrons so now there are 4 electrons in the delocalised system being shared over 5 carbon atoms to give a positive charge
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How is the delocalised system restored in the nitration of benzene?
When the C-H bond breaks in benzene, a pair of electrons and an orbital are returned to the delocalised system
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What is the catalyst in the nitration of benzene? Why?
Sulfuric acid because it lost a hydrogen atom to form the nitronium ion but then it gains the hydrogen atom when the C-H bond is broken
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State two reducing agents and which one is stronger
Lithium aluminium hydride - stronger and sodium borohydride
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What are the chemical formulae for the two common reducing agents?
Lithium aluminium hydride = LiAlH4; Sodium borohydride = NaBH4
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What can the two reducing agents reduce?
Lithium aluminium hydride can reduce carboxylic acids, aldehydes and ketones; Sodium borohydride can reduce aldehydes and ketones
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Why is sodium borohydride often used in reduction reactions?
It is easier to use
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As well as a reducing agent, what else is required for organic reduction reactions?
Methanol
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What is the chemical equation when ethanal is reduced into ethanol?
CH3CHO + 2[H] --> CH3CH2OH
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What is a carboxylic acid reduced into?
Primary alcohol without the aldehyde stage
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What allows a carboxylic acid to be reduce straight to a primary alcohol?
Stronger reducing agent (lithium aluminium hydride)
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How do you get an aldehyde by reducing a carboxylic acid?
Reduce a carboxylic acid to a primary alcohol and then oxidise it to an aldehyde
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What type of oxidation is it when you oxidise by distillation?
Partial oxidation
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What is required for a carboxylic acid to be reduced to a primary alcohol?
Lithium aluminium hydride dissolved in ethoxyethane; H+ or water
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What is nitrobenzene reduced into?
Phenylamine
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What is the reducing agent in the reduction of nitrobenzene?
A mixture of tin and concentrated hydrochloric acid
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How is the reduction of nitrobenzene done?
Heat the nitrobenzene with a reducing agent. Then add sodium hydroxide
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Write two equations for the reduction of nitrobenzene
C6H5NO2 + H+ + 6[H] --> C6H5NH3+ + 2H2O; C6H5NH3+ + OH- --> C6H5NH2 + H2O
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What is formed when a halogenoalkane has NaOH added to it with heat?
Alcohol
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What is meant by the retrosynthetic approach?
Scientists start with the target molecule and work backwards using known reactions to get an appropriate and readily available starting material
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Can propan-2-ol be oxidised into propanoic acid? What must be done instead?
No the propene must first be converted to an alkane
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How do you go from an alkane to a carboxylic acid without becoming an alkene?
Alkane --> Halogenoalkane (free radical substitution) --> Alcohol --> Carboxylic acid
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When calculating synthetic pathways for compounds with benzene, what is the requirement for them to behave the same as other compounds?
The functional group must not be directly attached to the benzene ring
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Other cards in this set

Card 2

Front

Give an example of the catalyst used for when chlorine reacts with benzene

Back

Aluminium chloride

Card 3

Front

What is formed when benzene reacts with chlorine?

Back

Preview of the front of card 3

Card 4

Front

What would the product be called in iodine reacted with benzene?

Back

Preview of the front of card 4

Card 5

Front

What is the reaction called when a halogen reacts with benzene?

Back

Preview of the front of card 5
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