Flashcards
Aromatic compounds
Cards in this deck (44)
- 1Which two scientists came up with ideas about the structure of benzene? Whos was proved to be correct?-Kekule and Pauing
-Pauling - 2What did Kekule believe?-He believed that the structure of benzene was cyclic with alternating double bonds
- 3What were four of the criticisms of Kekules structure?-It did not readily undergo electrophillic addition..didnt decolourise bromine
-The four isomers that are expected to be made when with bromine showed that 1,2 and 1,6 were the same
-Kekules strucutre implied that benzene should have a hydrogenation enthalpy of -360 however it was a lot lower
-The bond angles in Kekules structure show that it should be an irregular shape however studies show that the bond angles are perfectly 120 and planar - 4How did Kekule manage to save his idea?-The idea of resonance; he said that the locations of the double bonds are rapidly interchanging so molecules cant react, causing lack of reactivity
- 5What was Pauling's take on the structure on benzene?-That benzene is a six carbon shape with sigma bonds between each carbon atom and a hydrogen.
-The fourth electron is in the p orbitals which overlap, creating a ring above and below the plane
-This overlap causes the fourth electrons to become delocalised - 6What are some rules to naming aromatic compounds?1. Carbon 1 is the carbon attached to the group that has precedence
2. Precedence can be given to the group according to the alphabet
3. If there are three groups and 1 is different, that group takes presedence - 7How do you get a phenyl group?-By removing a hydrogen and attaching something else
- 8When is "benzene" used as the stem of a name?-When there is only one group attached to the benzene ring
- 9What is another name for ethanoic acid?-Acetyl Acid
- 10What is an electrophile?-A species attracted to an electron rich area
- 11What is an electrophillic substitution reaction-A reaction involving an electrophile, an electron rich area and the accepting of an electron pair
- 12What are the three steps in Nitration of benzene-Formation of the electrophile
-The attack of the electrophile (to the delocalised pi system)
-The reformation of the catalyst - 13What are some of the purposes-Nitrated arenes can be use din explosives (TNT)
-They can also be used for dyes - 14What are the different reactions of benzene that are basically electrophillic substitutions?-Nitration of benzene
-Alkylation of benzene
-Chlorination of benzene
-Acylation of bensene - 15What are the three types of Fredel-Craft reactions?-Alkylation
-Acylation
-Hydrogenation - 16What are the three stages in all of the Friedel-Crafts reactions?-Electrophile formation
-Substitution reaction
-Catalyst reformation - 17How is the electrophile production different between halogenation and alkylation/acylation-In halogenation, the halogen must react with a halogen carrier (Iron halide, iron or Aluminium Halide). The electron carrier polarises the halogen bond, causing it to be broken via heterolytic fission
-Alkylation/ acylations use a catalyst to form the carbocation - 18What are the conditions of electrophillic substitution?-Reflux
-50-55 degrees
-ANHYDROUS CONDITIONS
-Catalyst AlCl3 - 19What are the two halogen carriers you need to know?-Iron or Aluminium
- 20GO!!! STATE THE CONDITIONS, REACTANTS AND CATALYSTS FOR THE NITRATION OF BENZENE!!!!Conditions; 50-55 degrees, under anhydrous conditions, reflux
-Reactants: benzene + CONC nitric acid
Catalyst: CONC sulfuric acid - 21GO!!! STATE THE CONDITIONS, REACTANTS AND CATALYSTS FOR THE ALKYLATION OF BENZENE!!!!-Conditions; 50-55 degrees, reflux, under anhydrous conditions
Reactants; Benzene + halogenoalkane
Catalyst: AlCl3 - 22Why do the alkylations and acylations need to have a chloroalkane?-Because the catalyst is ALCl3, when forming the carbocation, the Cl joins with the AlCl3 to form AlCl4-.
-The AlCl4- can then give a Cl to the H+ ion in the reformation stage - 23Why is benzene more resistant to bromination than cyclohexene?-It all comes down to the fact that the delocalised electrons are spread all over the six carbons.
-This means that they are not as DENSE, so not strong enough to induce dipole
-The pi system is too stable to readily add benzene - 24What does a halogen need in order for it to become polarised?-A high charge density
- 25Why cant Na+be a halogen carrier?-It needs to form a covalent bond
-Na+ would form ionic bonds - 26What is the explaination of such low hydrogenation enthalpies and that it doesnt undergo electrophillic addition reactions readily?-It is such a stable molecule
- 27In terms of benzene, what is a delocalised electron cloud?-When the fourth electron is not just delocalised between two carbons but all six
- 28How do you identify a phenol?When an OH group is directly attached to the benzene ring
-Always say HYDROXYL GROUP not hydroxide - 29What are the properties of phenols?-Soluble in water but a weak acid as one H+ is released
-Solid at room temp - 30What do you get when you react a phenol with NaOH?-Salt and water (neutralisation via electrophillic substitution)
-A salt is when a hydrogen from an acid is replaced by a metal or ammonium ion
-So H in OH will be replaced - 31What can you say about the structure of phenols-Have an OH attached to benzene ring
-One lone electron pair from -OH goes to the delocalised ring.
-This loss makes the OH bond weaker, until H+ is given off
-But dont worry, the electron pair offered stabilises the phenoxide ion
-It also makes it more reactive to Electro. substitution than benzene - 32Why don't phenols need a catalyst for electrophillic substitution?-Phenols are more susceptible to electrophile
-This is because the O atom in the OH groups direct electrons to the ring, making it more negative
-This means that it is more reactive so doesn't need much help - 33Why would phenol require milder conditions than benzene in nitration?-Phenols lone pair in OH group makes ring more nucleophillic
-More susceptible to attack - 34How does the OH group increase the reactivity of phenol?-The p orbital of O OVERLAPS with the p orbitals of the Carbons, so the lone pair is donated to the delocalised pi system.
-This increases the electron density and makes it more susceptible to attack of a electrophile - 35What reactions can be carried out by a phenol?-Phenols are weak acids, so they can undergo acid-based reactions and a few alcohol reactions
- 36How does the CH3 group effect the rate and position of the electrophile?-CH3 is on the dream team, along with NH2 and OH
-They are the activators which are electron releasing
-They make the pi system more dense and therefore more readily attacked by electrophiles - 37Who is on the deactivating team aka the slow team?-These are the electron withdrawing groups: -NO2, -COOH -C=O
- 38Define a phenolAn aromatic compound where the hydroxyl group is directly attached to the benzene ring
- 39"Phenols are acids so they react with all bases"1. Take a look at the STRENGTH of the base
2. Phenol is a weak acid so wont react with a weak base like Na2CO3 - 40AYYYYYY what's TCP?TCP is a phenol!
-It stands for TriChloroPhenol!
-Halogenated Phenols are for antiseptics! - 41Phenols and ethanols both contain a OH groups but may react in different ways. Give an exampleWith carboxylic acids
-Ethanol would produce an ester but phenol wouldn't - 42Phenols and ethanols both contain a OH groups and may react in the same way. Give an example-When both PHENOL and ETHANOL react with NaOH, they BOTH produce:
-Salt
-Hydrogen - 43Say you already have a phenol.... and theoretically, you want to add another hydroxyl group. Which positions is the hydroxyl group most likely to go and why?-Well there is already on C1
-OH is an electron releasing and an activating group
-So it will be directed to groups 2,4 or 6 - 44—
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- A level Chemistry Flashcards on Aromatic compounds, created by Sparkle Shine on 14/09/2017.
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- Sparkle Shine · Sep 2017
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- Jan 5, 2018
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