F324 - Rings, Acids and Amines Flashcards
What does the current model for benzene comprise?
Each carbon atom in the cyclic compound contributes one electron to the overlapping p orbitals to form a pi bond. The pi bonds are delocalised (as are the electrons) over the six carbon atoms.
What did Kekule’s structure of benzene comprise of?
Cyclic molecule with alternating single and double carbon-carbon bonds.
What evidence is there to support the delocalised model of benzene?
The bond lengths are all equal and intermediate those for single and double carbon-carbon bonds, resistance to reactions and much slower reactions, particularly addition reactions. Higher enthalpy of hydration values compared to alkenes.
What is the most common type of reaction arenes undergo?
Electrophilic substitution
Why do arenes undergo substitution reactions over addition reactions?
The arenes are able to retain their delocalised pi electron structure in substitution reactions by replacing a hydrogen on one of the carbon atoms. This structure is broken in addition reactions.
What is the name of the product formed when an -OH group is attached to the benzene ring?
Phenol
What are the resulting products when phenol reacts with sodium hydroxide?
Sodium phenoxide and water
What are the resulting products when phenol reacts with sodium?
Sodium phenoxide and hydrogen gas
Why does phenol react with bromine easily when benzene does not?
The -OH group on the phenol donates an electron-pair to the benzene ring from the oxygen p-orbital to extend the delocalisation making the ring more susceptible to electrophilic attack. (It activates the ring by increasing the charge density, particularly at positions 2, 4 and 6)
What are phenols used for?
Plastics, antiseptics, disinfectants and resins for paints.
What is the resulting type of product for red from the oxidation of a primary alcohol under distillation?
Aldehyde
What is the resulting type of product formed from the oxidation of a primary alcohol under reflux?
Carboxylic acid
What is the resulting type of product formed from the oxidation of a secondary alcohol under reflux?
Ketone
What is the resulting type of product formed from the oxidation of a tertiary alcohol?
No reaction
What is the carbonyl functional group?
C=O
Which types of compounds contain the carbonyl functional group?
Aldehydes, ketones, carboxylic acids and esters
What is formed from the reaction of a carbonyl compound with NaBH4?
Alcohol
What is used to detect the presence of a carbonyl compound?
2,4-dinitrophenylhydrazine which will form a deep yellow/orange precipitate if present. (Only aldehydes and ketones)
After the reaction with 2,4-dinitrophenylhydrazine what can be done to determine the identity of the unknown carbonyl compound?
Compare melting points after recrystallisation.
What is the Tollens’ reagent used to detect?
Aldehydes
How are aldehydes and ketones identified from one another and what are the results for these tests?
Oxidised with acidified potassium dichromate.
Aldehyde - orange to green solution (oxidised to carboxylic acid)
Ketone - no change (cannot be oxidised further)
Tollens’ reagent - aqueous solution of silver nitrate in excess ammonia
Aldehyde - silver mirror forms from colourless solution (Ag is reduced)
Ketone - no reaction (cannot be oxidised so cannot reduce silver)
What causes carboxylic acids to be soluble in water?
A small percentage of molecules will ionise by losing the H+ on the -OH group, some will for hydrogen bonds with water molecules via the -OH group, and some will form dipole-dipole interactions via the C=O group.
What is formed in the reaction of a carboxylic acid and a metal?
Salt (carboxylate) and hydrogen gas
What is formed in the reaction of a carboxylic acid and a base (e.g. metal oxide)?
Salt (carboxylate) and water
What is formed in the reaction between a carboxylic acid and a metal carbonate?
Salt (carboxylate), water and carbon dioxide
What is the general word equation for esterification?
Carboxylic acid + alcohol ester + water
What is the type of product formed between an acid anhydride and an alcohol?
Ester
What are the advantages of producing esters using acid anhydrides?
Reaction is not reversible and no catalyst is needed.
What is formed when an ester reacts with hot aqueous acid?
Carboxylic acid and alcohol
What is formed when an ester reacts with hot aqueous alkali?
Carboxylate salt and alcohol
What are esters used for?
Perfumes and flavourings
What is a triglyceride?
A compound formed when all three of the alcohol groups in propane-1,2,3-triol (glycerol) have been esterified using fatty acids.
What is a fatty acid?
A carboxylic acid obtained from oils or fats.
What are the main structural features of a fatty acid?
Tend to contain an even number of carbon atoms, have no C=C double bonds and form unbranched chains.
What is a monosaturated fatty acid?
Fatty acids with one C=C double bond.
What are polysaturated fatty acids?
Fatty acids with more than open C=C double bonds.
Which type of fatty acids will have stereoisomers?
Mono or polysaturated fatty acids.
Why is it thought that trans fatty acids lead to heart problems?
Trans fats increase the amount of low density lipoprotein (‘bad’ cholesterol) which causes an imbalance in your blood leading to arteries furring up and narrowing causing circulatory problems resulting in high blood pressure, strokes and heart disease.
What are esters of fatty acids used for?
Biodiesel
What is the advantage and disadvantage to using biodiesel?
Advantage - considered to be carbon neutral and comes from a renewable resource
Disadvantage - land use has been transferred from food crops to plants for fuels causing a need to more land to be turned into fields
How are amines prepared?
Nucleophilic substitution of a halogenoalkane with excess hot ethanolic ammonia.
How is phenylamine prepared?
Reduction reaction of a nitrobenzene using tin and concentrated hydrochloride acid.
How are amines able to behave as bases?
The lone-pair of electrons on the nitrogen atom can readily accept a proton.
What are the products formed from the reaction of an amine with an acid?
Salt and water
How are azo dyes produced?
Phenylamine reacting with nitrous acid below 10 degrees C to form a diazonium ion, which is then coupled with a phenol under alkaline conditions.
Why are diazonium dyes stable?
The delocalisation of the diazonium ion pi bonding electrons over the benzene ring stabilises the ion group allowing for the formation of dyes at very low temperatures.
