Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
30 Cards in this Set
- Front
- Back
|
What is the evidence disproving kekulés model of the benzene ring? |
Benzene wouldn't undergo electrophilic addition reactions such as decolourising bromine water (so it didn't have C=C)
The model has C-C and C=C but benzene had bonds that were all the same length
Hydrogenation enthalpy was a lot lower than expected |
|
|
What is the structure of the delocalised structure of benzene and what is the bonding? |
Cyclic hexagonal hydrocarbon with rings of electron density above and below the C ring
There is a sideways overlap of p orbitals creating a system of delocalised π electrons
2 electrons are used to bond with a C atom, 1 is used to bond with an H atom and 1 is used in a p orbital |
|
|
What is the preffix of benzene and when is it used? |
Phenyl When there is a C chain longer than 6 C long or when there is an alkyl group with a functional group attached |
|
|
What is a COOH, CHO, NH2, COO, CO group attached to a benzene ring called? |
Benzoic acid, benzaldehyde, phenylamine, phenylethanoate, phenylethanone |
|
|
What are the 2 Electrophilic substitution reactions using nitric acid for benzene and the conditions? |
Nitration with HNO3, H2SO4 catalyst at 50°C forming a nitrobenzene and water Nitration with excess HNO3, H2SO4 catalyst at 70°C forming a dinitrobenzene and water |
|
|
What is the electrophile in a nitration reaction? |
Nitronium ion (NO2+) |
|
|
What is the reaction mechanism of the nitration of a benzene? |
1. HNO3 reacts with H2SO4 to produce the nitronium ion 2. This accept an electron pair from the benzene ring to form a dative covalent bond 3. This intermediate breaks down to give nitrobenzene and H+ 4. H+ reacts with HSO4- to regenerate intermediate |
|
What is the reaction mechanism for the nitration of benzene? |
|
|
|
What is needed for the halogenation of a benzene? |
A halogen carrier catalyst such as FeBr3 or AlCl3 depending on whether it's bromination or chlorination |
|
|
What is the equation for the bromination of a benzene? |
Benzene + Br2 -> Bromobenzene + HBr (With halogen carrier) |
|
|
What is the reaction mechanism of the bromination of a benzene? |
1. The electrophile Br+ (bromonium) is generated when bromine reacts with a halogen carrier 2. This electrophile accept an electron pair from the benzene ring and forms a dative covalent bond 3. The intermediate breaks down and gives bromobenzene and H+ 4. H+ reacts with FeBr4- to regenerate catalyst and form HBr |
|
|
What is needed for an alkylation reaction and what is the general equation? |
Halogen carrier catalyst to generate electrophile and this depends on whether there's chlorine or bromine in the molecule Benzene + Haloalkane -> Alkylbenzene + H halide |
|
|
What is needed for acylation reactions and what is the general equation? |
Acyl chloride such as CH3COCl and halogen carrier catalyst
Benzene + Acyl chloride -> Phenylalkylone + H halide |
|
|
Why are arenes less reactive than alkenes? |
They have delocalised π electrons above and below the carbon ring so the electron density around any two C atoms is less than that of C=C |
|
|
Why doesnt bromine react with benzene at RTP? |
There is insufficient π electron density around any 2 C atoms to polarize the bromine molecule |
|
|
Why are phenols weak acids? |
They partially dissociate to form a phenoxide ion |
|
|
What happens when there is an alkyl chain with an OH group on a benzene? |
The benzene becomes phenyl and the name of the alkyl chain is the suffix |
|
|
What answers to Alcohols react with ... Bases Phenols react with ... Bases Carboxylic acids react with ... Bases |
No Strong Weak and strong |
|
|
Why are phenols more reactive than benzenes? |
The lone pair on the O in the OH is donated to the ring of delocalised electrons in the benzene causing it to be more electron dense and attract electrophiles more strongly |
|
|
What are the 2 electrophilic substitution reactions of a phenol and what are the products? |
Bromination which forms a tribromophenol and HBr Dilute nitration which forms a mixture of 2- and 4- nitrophenol and water |
|
|
What activates and deactivates a benzene ring and what does this mean? |
2- and 4- directing Groups (except halogens) 3- directing groups Activating means that it reacts more readily with electrophiles |
|
|
What are the 2- and 4- directing groups? |
F, Cl, Br, I OR NH2 or NHR R or C6H5 OH
Felix or Nick roared 'Oh' |
|
|
What are the 3- directing groups? |
NO2 NR3 + CN CHO COOR RCOR SO3H COOH Noah, Nraine, Cynthia, Cho, Coorie, Rcord shouted "cooooooh" |
|
|
How can you separate a mixture of products in solids and liquids? |
Distillation if they are liquids or recrystallization if they are solid |
|
|
What do you need to remember when drawing horseshoes in a reaction mechanism? |
The empty section needs to face the part of the molecule that is electron deficient |
|
|
What is the white precipitate formed when phenol reacts with bromine? |
2,4,6 tribromophenol |
|
|
How do you form sodium phenoxide? |
Add NaOH to phenol |
|
|
What is the mechanism for the nitration of bromophenol? |
1. NO2+ accepts a lone pair from the benzene ring forming a dative covalent bond 2. The intermediate breaks down with the Br donating an electron pair to the benzene ring 3. This forms nitrophenol and Br+ |
|
|
What are the products of the reaction between concentrated nitric acid and phenol? |
2,4,6 trinitrophenol |
|
|
Why is COOH group on benzene harder to nitrate? |
COOH is an electron-withdrawing group |
