13813612
Descripción
Fichas por Amelia Wilson, actualizado hace más de 1 año
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Creado por Amelia Wilson
hace más de 6 años
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| Pregunta | Respuesta |
| Homolytic fission | each atom in a covalent bond gets one electron, producing free radicals |
| Heterolytic fission | one atom gets both electrons when a covalent bond is broken. |
| free radicals | reactive species which possesses an unpaired electron |
| What type of reaction occurs between a halogen and an alkene? | Free radical substitution |
| Type of reaction, Reagents, conditions and stages of free radical substitution to form a haloalkane | Type of reaction: Free Radical substitution Reaction taking place: Halogenation Reagents: Alkane + halogen (eg. Br2) Conditions: UV light Three stages: initiation reactions, propagation reactions, termination reactions |
| what is a double bond made up of? | A sigma-bond and pi-bond. |
| What makes alkenes more reactive? | The pi-bond in the double bond is formed from the overlap of p-orbitals. These pi-bonds are much weaker than sigma-bonds due to the spread of electron density above and below the molecule, so there's weaker electrostatic attraction between the nuclei and electrons. This means that it is more likely to be attacked by electrophiles. |
| Electrophile | electron-pair acceptor |
| Type of reaction alkenes go through | Electrophilic addition reactions |
| Markownikoff's rule | H adds to the carbon with the most H atoms already attached as this is the more stable carbocation. |
| What makes a carbocation more stable? | more alkyl groups = more stable because the alkyl groups are electron releasing and reduce the charge on the positive carbon atom, stabilising it. |
| Test for C=C double bond | Shake with orange bromine water. positive = goes colourless (because Br is added across the double bond to form a dibromoalkane) |
| production of alkanes from alkenes | Reagents: Alkene + Hydrogen Conditions: Ni catalyst, 150 degrees Celcius Reaction taking place: Hydrogenation |
| Formation of alcohol from an alkene |
Reagents: alkene, steam
Conditions: 300 degrees Celsius, 60-70 atm,
H3PO4 catalyst
Reaction taking place: Hydration
Type of reaction: electrophilic substitution
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| products of complete combustion of alcohols | carbon dioxide and water |
| Formation of haloalkanes from alcohols (reagents, conditions, type of reaction) | Type of reaction: substitution reaction Reaction taking place: Halogenation Reagents: alcohol, halide ion Conditions: acid catalyst (H2SO4) |
| Dehydration of alcohols |
Type of reaction: Elimination reaction
Reagents: alcohol, conc. H2SO4
Conditions: Heat under reflux
Products: Alkene and water
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| Oxidation of Primary Alcohols |
Reagents: alcohol, potassium dichromate solution [O]
Conditions: Distil for aldehyde, reflux for carboxylic acid
Observation: orange dichromate(VI) ion is reduced to the green chromium(III) ion, Cr3+
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| Oxidation of Secondary Alcohols |
Reagents: alcohol, potassium dichromate solution [O]
Conditions: Distil for ketone
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| Oxidation of Tertiary Alcohols |
Cannot be oxidised
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| Haloalkane | An alkane with halogen atoms |
| Nucleophile | electron-pair donator |
| Reactivity of haloalkanes | Halogens are much more electronegative than C, so the C-X bond is polar. The delta+ C is electron deficient, so attracts nucleophiles to undergo nucleophilic substitution reactions. |
| Hydrolysis of haloalkanes |
Type of reaction: Nucleophilic Substitution
Reaction taking place: Hydrolysis
Reagents: haloalkane, NaOH
Conditions: warm aqueous alkali, reflux
Product: Alcohol
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| Rate of substitution reactions with haloalkanes | As polarity of the halide decreases (down the group), C is less attracted to nucleophiles, so the rate decreases. However, as bond strength decreases (down the group), the bond breaks more easily, so rate increases. overall order (fastest to slowest): iodoalkane, bromoalkane, chloroalkane, fluoroalkane. |
| Formula of benzene | C6H6 |
| Comparison of Kekule's model and the delocalised model for benzene | Kekule: Alternating single and double bonds. P-orbitals overlap between two C atoms Localised electron density in pi-bonds. Delocalised: P-orbitals of all 6 C atoms overlap to create a pi-system Pi-system made up of two rings of delocalised electrons above and below the plane of the molecule. Equal length C-C bonds |
| Evidence for the delocalised model of benzene | 1. Normally, the length of C-C bond is 154pm and C=C bond is 134pm, but in benzene, all C-C bonds are 140pm. 2. Enthalpy change of hydrogenation for cyclohexene is -120 kJ/mol so is Kekule was right, it would be 3 times this for benzene (-360 kJ/mol) but it is actually -208 kJ/mol. This is less exothermic than expected. 3. Benzene should react with bromine water at room temperature like alkenes, but it is actually only possible in the presence of a halogen carrier or high temp. So it is more stable than an alkene. |
| Aromatic compound | compounds containing a benzene ring |
| What makes benzene more stable than alkenes? | In benzene, electrons are delocalised, in alkenes they are localised between two carbon atoms. This means that benzene has a lower electron density than alkenes, so benzene is unwilling to undergo addition reactions because it is too stable. |
| What reactions to arenes undergo? |
Electrophilic substitution reactions.
(A hydrogen atom is replaced by an electrophile)
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| Halogen Carrier |
They make compounds into stronger electrophiles. They accept a lone pair of electrons from a halogen atom on an electrophile and as the lone pair is pulled away, polarisation in the molecule increases, forming a carbocation. This makes the electrophile stronger, allowing halogens to substitute into the benzene ring.
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| Halogenation of Benzene | Type of reaction: Electrophilic Substitution Reaction taking place: Halogenation Reagents: Halogen, halogen carrier Conditions: halogen carrier catalyst (AlCl3) Product: halobenzene |
| Friedel-Crafts alkylation |
Form C-C bonds by putting an alkyl group onto a benzene ring using a haloalkane and halogen carrier, and reflux.
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| Friedel-Crafts acylation |
Substitutes an acyl (C=O) group for a H on benzene. Reflux benzene with an acyl chloride and halogen carrier to produce phenylketones.
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| Production of nitrobenzene |
Reagents: Conc. nitric acid, benzene
Conditions: warm, conc. H2SO4 catalyst, for mononitration temp needs to be below 55 degrees, otherwise multiple substitutions.
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| Phenol |
C6H5OH
Benzene ring with alcohol group attached
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| Why is phenol more reactive than benzene? | Lone pair of electrons from oxygen p-orbital overlap with the delocalised ring of electrons in the benzene ring, so it is partially delocalised into the pi-system. This increases electron density of the ring, making it more likely to be attacked by electrophiles. |
| Where do electron donating groups direct substitution? Give examples of electron donating groups. | Electron donating groups include -OH, and -NH2. They direct substitution to the 2-, 4-, and 6- carbons. |
| Where do electron withdrawing groups direct substitution? Give examples of electron withdrawing groups. | Electron withdrawing groups include -NO2. They direct substitution to the 3- and 5- carbons because it withdraws electron density at the 2-, 4- and 6- carbons, so they can't react with electrophiles. |
| Reaction of phenol with bromine water |
Reagents: bromine water (Br3)
Type of reaction: electrophilic substitution
products: 2,4,6-tribromophenol and HBr
observation: orange to colourless
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| Nitration of phenol |
Reagents: dilute nitric acid
Type of reaction: electrophilic substitution
Products: 2-nitrophenol, 4-nitrophenol
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| Phenol with bases (NaOH) |
Phenol is weakly acidic so will undergo typical acid-base reactions.
Reagents: NaOH
Conditions: room temp
Products: sodium phenoxide and water
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| Carbonyl compounds | Aldehydes and ketones Contain C=O group |
| Reduction of aldehydes and ketones | Type of reaction: nucleophilic addition Reagent: reducing agent [H] NaBH4 (sodium tetrahydriborate (III) or sodium borohydride), then water Products: alcohol |
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