Rings, acids and amines Flashcards
Describe the structure of Benzene.
- Planar hexagonal hydrocarbon
- 3 valance electrons to bind to 2 carbon atoms and 1 hydrogen atom.
- The fourth electron is found on the p-orbital at a right angle to the plane (120).
- Adjacent p-orbitals overlap sideways on each side to form a ring of electron density above and below the plane.
- Delocalised p-electron system)
What are the types of evidence for the structure of benzene?
Bond lengths
Enthalpy change of hydrogenation
Resistance to reaction
What is the evidence for bond length?
All six C-C bonds are the same length 0.139nm. Which shows there aren’t any alternative C=C bonds and single bonds (0.134nm).
What is the evidence for enthalpy change of hydrogenation?
Expected to have three times the energy as cyclohexene. (-360kjmol^-1).
However benzene has an enthalpy change of -208.
Therefore shows that benzene is 152 more stable than Kekule structure and why it doesn’t react like alkenes.
What is the evidence for resistance to reactions?
If contained C=C bonds, it would similarly to alkenes.
However does not decolourise in bromine water or takes part in electrophilic addition reactions.
Why is a halogen carrier needed in the process of bromination of benzene?
The delocalised pi electrons make benzene more stable. The electron density is higher in alkenes because of the localised electrons, therefore electrophiles are more attracted.
Why there is more of a relative ease of bromination of phenol compared with benzene?
- A lone pair of electrons on the oxygen atom in the phenol group is drawn into the benzene ring.
- This creates a higher electron density in the ring structure and the ring is activated.
- This increased electron density polarises bromine molecules, which are then attracted more strongly towards the ring structure in benzene.
What are the uses of Phenols?
In the production of plastics, antiseptics, disinfectants and resins for paints.
What type of mechanism involves conc.HNO3?
Electrophilic substitution
What are examples of halogen carriers?
Iron, iron halides and aluminium halides.
What are the uses of phenol?
plastics, antiseptics, disinfectants and resin for paints.
What is the reducing agent?
NaBH4
What mechanism is used to reduce aldehydes and ketones?
Nucleophilic addition
What is Brady’s solution?
2,4- dinitrophenylhydrazine
What does Brady’s solution do?
Detects the presence of a carbonyl group in an organic compound.
How does Brady’s solution detect carbonyl compounds?
By producing a red-brick precipitate which can be used tot measure the melting point of the derivative.
What is the chemical name of Tollen’s reagent?
ammoniacal silver nitrate
What effect does Tollen’s reaction have on ketones and aldehydes?
Ketones- nothing
Aldehydes- acts as a oxidising agent and silver ions are reduced to silver.
Produces silver mirror effect
What is an alternative method to reducing carbonyl compounds?
React with hydrogen under a nickel catalyst
Explain the solubility of carboxylic acids.
Very soluble in organic solvents.
More hydrogen bonds are made with the water and more dipole-dipole interactions.
As the carbon chain increases the solubility decreases.
What is the acidity of carboxylic acids?
Weak monobasic acids
What happens when a CA reacts with a metal?
Produces a salt and hydrogen
What happens when a CA reacts with a carbonate?
Produces a salt, carbon dioxide and water
What happens when a CA reacts with a base?
Salt and water
