Topic 6: Organic Chemistry I Flashcards Preview

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Flashcards in Topic 6: Organic Chemistry I Deck (84):

How can alcohols be made from alkenes?

- alkenes are hydrated by steam
- at 300 degrees
- 60-70 atm
- solid phosphoric (V) acid catalyst
- ethanol to ethene


What is the general formula of aldehydes and ketones?

- CnH2nO


What are carbonyl compounds?

- have the functional group C=O


What are electrophiles?

- electron pair acceptors
- often positively charged ions or partially positive areas
- electron poor, so attracted to electron rich areas
- react with negative ions, atoms with lone pairs and electron rich area around C=C double bond


What happens when you react alcohols with PCl5

- produces chloroalkanes
- ROH + PCL5 = RCl + HCl + POCl3


Define homologous series

- a group of organic compounds that have the same functional group and general formula


What two types of isomers do we need to know?

- structural isomers
- stereoisomers


What is the problem with free radical substitution and how to solve?

- it's hard to get a particular product as you end up with a mixture of products
- you may end up with dichloromethane, trichloromethane, tetrachloromethane, chloromethane

- solve by having an excess of methane

- another problem is that radical substitution can occur at any point along the carbon chain so a mixture of structural isomers can be formed


What is an aldehyde?

- aldehydes have a hydrogen and one alkyl group attached to the carbonyl carbon atom
- e.g. propanal


Describe the reaction mechanism for free radical substitution

- radicals are produced
- photodissociation occurs breaking the Cl-Cl bond
- homolytic fission occurs meaning 2 Cl. radicals are made because of the unpaired electron

- radicals are used up and created in a chain reaction
- Cl. attacks a methane molecule [Cl. + CH4 = .CH3 + HCL]
- the new methyl radical, .CH3 can attack another Cl2 molecules [.CH3 + Cl2 = CH3Cl + Cl.]
- the new Cl. can attack another CH4 molecule until all Cl2 or CH4 molecules have reacted

- radicals react together to form stable molecules
- e.g. Cl. + .CH3 = CH3Cl
- e.g. .CH3 + .CH3 = C2H6


What happens when halogenoalkanes react with an ethanol alkali?
- draw equation

- halogenoalkanes undergo elimination reactions
- if you react a halogenoalkane with warm alkali dissolved in ethanol, you get an alkene
- must be heated under reflux
- the hydroxide ions are acting as a base to remove an H+ ion from the halogenoalkane


Are combustion reactions exothermic or endothermic?

- exothermic


Give the definition of general formula

- an algebraic formula that can describe any member of a family of compounds


What is reforming

- converting straight-chain alkanes into branched chain alkanes and cyclic hydrocarbons
- using catalyst (platinum stuck on aluminium oxide)
- at 500 degrees

- H2 gas produced


How do you oxidise an alkene?

- oxidised by acidified potassium manganate(VII)
- purple solution is decolourised
- makes a diol (two OH groups)
- e.g. ethene to ethane-1,2- diol


How do you form bromoalkane from an alcohol?

- the OH can be swapped for bromine in a substitution reaction
- reaction require an acid catalyst e.g. 50% concentrated H2SO4


Describe functional group isomers

- the same atoms can be arranged into different functional groups

- thye have very different physical and chemical properties


Why is the carbon-halogen bond polar?

- halogens are generally more electronegative than carbon


What is addition polymerisation?

- double bonds in alkenes open open and join together to make long chain called polymers


How to form alkenes from alcohols?

- eliminating water from alcohols in an elimination reaction
- alcohol is mixed with an acid catalyst such as phosphoric acid (H3PO4)
- mixture is then heated
- when an alcohol dehydrates it eliminates water
- e.g. ethanol dehydrates to form ethene


Why are there two possible alkene products when water from alcohols are eliminated?

- depends on which side of the hydroxyl group the hydrogen is eliminated from


What are curly arrows?

- they show how electron pairs move around


How do alcohols form halogenoalkanes?

- alcohols react in substitution reactions to form halogenoalkanes


What is bond fission?

- breaking a covalent bond


What is cracking?

- cracking is breaking long-chain alkanes into smaller hydrocarbons
- breaks C-C bonds


What halogenoalkane reacts fastest?

- iodoalkanes


Why do pi bonds have a relatively low bond enthalpy?

- the electron density is spread out above and below nuclei
- this causes the electrostatic attraction between the nuclei and the shared pair of electrons to be weaker than in sigma bonds


How can you test whether a compound is an aldehyde or a ketone?

- using benedict's solution
- which is a blue solution of copper(II) ions dissolved in sodium carbonate
- if it's heated with an aldehyde, the blue copper(II) ions are reduced to a brick-red precipitate of copper (I) oxide
- if it's heated with a ketone, nothing happens as ketones cannot be easily oxidised


What is a functional group

- a group of atoms in a molecule responsible for the characteristic reactions of that compound


Describe catalytic cracking

- uses zeolite catalyst (hydrated aluminosilicate)
- at a slight pressure
- high temp 450 degrees
- mostly produces aromatic compounds (contain benzene rings) and motor fuels
- using catalyst cuts cost because it can be done at lower pressure and temp


Describe and draw the nucleophilic substitution mechanism

- C-X bond breaks heterolytucally, both electrons are taken by the halogen
- nucleophile bonds to the carbon


How do halogenoalkanes react with aqueous KOH to form alcohols?
- draw it

- halogenoalkanes react with hydroxide ions by nucleophilic substitution to form alcohols
- use warm aqueous potassium hydroxide and do it under reflux


What is the strongest type of covalent bond?-

- sigma bonds
- high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and shared pair of electrons
- sigma bonds have a high bond enthalpy


Describe heterolytic fission

- the bond breaks unevenly with one of the bonded atoms receiving both electrons from the bonded pair
- two different substances can be formed
- e.g. a positively charged cation and a negatively charged anion


Give examples of nucleophiles that react readily with halogenalkanes

- OH-
- NH3
- CN-
- H2O


What does bromine water test for?

- the presence of carbon-carbon double bonds
- when you shake an alkene with brown bromine water, solution decolourises as it formed colourless dibromoalkane


What are the two types of cracking?

- thermal cracking
- catalytic cracking


How does fractional distillation work?

- crude oil is vaporised at about 350
- goes into fractionating column and rises up through the trays

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What is a double covalent bond made up of

- a sigma and a pi bond
- pi bond formed when two lobes of two orbitals overlap sideways


What is the general equation of the hydrolysis of halogenoalkanes to alcohols?

- R-X + H2O = R-OH + H+ + X-


What is the general formula for alcohols?

- CnH(2n+1)OH


What does adding H to C=C bonds do?

- produces alkanes
- needs a nickel catalyst and 150 degrees
- e.g. ethene with H2 makes ethane


What type of bond are single covalent bonds in organic molecules?

- sigma bonds
- when two orbitals overlap
- gives highest possible electron density


Define skeletal formula

- shows the bonds of the carbon skeleton only, with any functional groups
- hydrogen and carbon atoms aren't shown


How do cyanide ions react with halogenoalkanes to form nitriles?
- write equation

- reflux a halogenoablkane with potassium cyanide in ethanol to form a nitrile by nucleophilic substitution


What are nucleophiles

- they are electron pair donors
- often negatively charged ions or a species that contain a lone pair of electrons
- electron rich so attracted to electron poor areas
- therefore, likely to reaction with positive ions and partially positive areas in molecules with polar bonds


Describe chain isomers

- the carbon skeleton can be arranged differently
- e.g. straight or branched

- these isomers have similar chemical properties but their physical properties will change due to the shape of the molecule


How do you compare the reactivities of halogenoalkanes using experiment?

- when you mix halogenoalkane with water it forms alcohol
- if you put silver nitrate solution in the mixture too, the silver ions react with the halide ions as soon as they form giving a silver halide precipitate
- set up three test tubes, ethanol (as solvent) and silver nitrate solution
- time how long precipitate forms


What is a catalytic converter

- use a platinum catalyst to change bad gases into safer gases
- e.g. 2NO + CO = N2 + CO2


How do halogenoalkanes react with ammonia to form amines?

- draw mechanism

- amines are organic compounds
- based on ammonia but one or more of the hydrogen atoms are replaces by alkyl group s
- if you warm a halogenoalkane with excess ethanol ammonia, the ammonia swaps places with the halogen to from a primary amine

- in the second step, the ammonia molecule removes a hydrogen from the NH3 group to leave an amine


Describe homolyitc fission

- the bond break evenly and each bonding atom receives one electrons from the bonded pair
- two electrically uncharged radicals are formed
- they are very active


What are alkanes

- they are saturated hydrocarbons
- general formula CnH(2n+2)


What do alkanes react with halogens to form?

- halogenoalkanes


What do primary alcohols oxidise to?

- aldehydes
- then to carboxylic acids


What do tertiary alcohol oxidise to?

- they don't oxidise


What is the only why to oxidise tertiary alcohols?

- by burning them


What is a halogenoalkane?

- an alkane with at least one halogen atom in pace of a hydrogen atom


Define displayed formula

- shows how all the atoms are arranged and all the bonds between them


What is a structural isomer and give the three types of structural isomers

- molecular formula is the same, but structural formula is different

- chain isomer
- positional isomer
- functional group isomer


What is a free radical substitution reaction?

- a hydrogen atom is substituted by a chlorine or bromine


How can two products form when alkenes react with hydrogen halides?

- if the alkene is unsymmetrical
-amount of each product depends on how stable the carbocation formed is
- carbocations with more alkyl groups are more stable
- more stable forms more


What forms when alkenes undergo addition with hydrogen halides

- form halogenoalkanes


How can you control how far the alcohol is oxidised?

- gently heating ethanol with potassium dichromate(VI) solution and sulphuric acid in a test tube should produce apple smelling ethanal , but you could end up with ethanoic acid
-- to get just an aldehyde, you need to get it out of the oxidising solution as soon as it is formed, you can do this by heating excess alcohol with a controlled amount of oxidising agent in distillation apparatus, so a;dehyde can be distilled immediately
-- to produce the carboxylic acid, the alcohol has to be vigorously oxidised, so heated with excess oxidising agent and under reflux


Draw the equation of oxidising secondary alcohols

- alcohol + [O] = ketone + H2O


What are isomers?

- two molecules that have the same molecular formula but atoms arranged differently


Definition of molecular formula

- the actual number of atoms of each element in a molecule


What is knocking

- where alkanes explode of their own accord
- straight chain alkanes most likely to cause knocking
- adding branched chains and cyclic hydrocarbons making knocking less likely so combustion more efficient


How do you make iodoalkanes from alcohol?

- reacting with phosphorus triiodide (PI3)
- 3ROH + PI3 = 3RI + H3PO3


Draw how primary alcohols can be oxidised twice

- go!


What happens when you react alcohols with HCl?

- produces chloroalkanes
- ROH + HCL = RCl + H2O
- fastest rate with tertiary alcohols
- slowest rate with primary alcohol


What is the general formula of cycloalkanes?

- CnH2n


Definition of structural formula

- shows the arrangement of atoms carbon by carbon with the attached hydrogens and functional groups
- e.g. CH3CH2CH2CH2OH


What conditions do you need for free radical substitution to occur?

- photochemical reactions
- the presence of UV light


What are radicals

- radicals have an unpaired electron
- they are very reactive
- they will react with anything


What do secondary alcohols oxidise to?

- ketones only


What do you need as an oxidising agent to mildly oxidise alcohols?

- acidified dichromate(VI)


What is a ketone?

- ketones have two alkyl groups attached to the carbonyl carbon atom
- e.g. propane


What do halogens reacting with alkenes form? and draw the mechanism

- dihalogenoalkanes


Describe thermal cracking

- takes place at high temp of around 1000
- high pressure (70 atm)
- produces lots of alkenes
- these alkenes makes polymers


Order the fractions of alkane molecules in a fractionating column

- gas C1-C4
- petrol
- naphtha/gasoline C5-C10
- kerosene C10-C16
- gas oil (diesel) C15-19
- mineral oil C20-30

- fuel oil
- wax, grease
- bitumen


What affects how quickly different halogenoalkanes hydrolyse?

- the carbon-halogen bond enthalpy
- weaker carbon-halogen bonds breaks more easily, so react faster
- bond enthalpy depends on the size of the halogen
- the larger the halogen, the longer the C-X bond, the lower the bond enthalpy
- the size of the halogen increases down group 7, so iodoalkanes have the weakest bonds, so hydrolysed fastest


Describe positional isomers

- the skeleton and the functional group could be the same, only with the functional group attached to a different carbon atom

- also have different physical properties and possibly different chemical properties


What is electrophilic addition?

- happens to alkenes
- the alkene double bond opens up and atom are added to the carbon atoms
- happens because double bond has got many electrons and is attacked by electrophiles


What is the definition of empirical formula?

- the simplest whole number ratio of atoms of each element in a compound