Topic 2 - Heterocyclic and Aromatic Chemistry Flashcards
What is produced when a primary amine reacts with a ketone?
An imine.
What is produced when a secondary amine reacts with a ketone?
An enamine.
What is tautomerism?
A reaction that only involves the intramolecular transfer of a proton.
What are the two forms of tautomerism for a ketone?
The ketone form (keto) and the enol form.
What are the two forms of tautomerism for an imine?
The imine form and the enamine form.
What are the names of the positions for substituted atoms in benzene?
1 - Ipso
2 - Ortho
3 - Meta
4 - Para
How are benzene structures named?
Multiple substituents are quoted in alphabetical order.
Priority is assigned using Cahn-Ingold-Prelog rules.
What is the bonding like in benzene?
All carbons are sp2 hybridised.
The p-orbitals overlap to form a continuous π system that is delocalised equally over each carbon atom.
How does the number of resonance forms link to stability?
The more resonance structures that can be drawn for a cation/anion, the more stable it is.
What are the four conditions for Hückel’s rule of aromaticity?
Planar
Cyclic
Fully conjugated
(4n + 2) π electrons where n is an integer (including zero).
What is pKa?
The measure of acidity and basicity.
It describes how much of the acid has been deprotonated and exists in its conjugate base form. The lower the pKa, the stronger the acid.
What is an acid?
A species with a tendency to lose a proton.
What is a base?
A species with a tendency to gain a proton.
What three factors affect the strength of an acid?
The stability of the conjugate base: electronegative atoms and inductively and mesomerically withdrawing groups will stabilise the conjugate base.
The H-A bond strength: H-A bond strength decreases down the periodic table due to size mismatch of atomic orbitals.
The solvent: The better the solvent is at solvating/stabilising ions, the easier it is for the acid to be deprotonated.
What is pKaH?
The measure of the strength of a base. A higher pKaH represents a stronger base.
What is the main factor that affects the strength of a base?
The availability of its lone pair of electrons.
Electronegative atoms and inductively and mesomerically withdrawing groups make the lone pair less available. This reduces the basicity.
How does the basicity of aniline compare with the basicity of cyclohexylamine?
Aniline is much less basic than cyclohexylamine.
This is due to the lone pair in aniline being <i> partially </i> delocalised into the aromatic ring.
How does the acidity of phenol compare with the acidity of cyclohexanol?
Phenol is much more acidic than phenol.
This is due to the resonance stabilisation of the conjugate base.
What are the features of the acidity of benzoic acid?
The benzoic acid anion cannot be stabilised through resonance. However, its acidity is still affected by substituents.
What is the bonding like in pyridine?
All carbon and nitrogen atoms are sp2 hybridised.
1 electron in the nitrogen p-orbital contributes to the π system.
The nitrogen lone pair is orthogonal to the ring and it is <b>not</b> delocalised.
The nitrogen atom causes lower HOMO and LUMO orbital energies than benzene.
What is the pKa for the protonation of alcohols?
0.
What is the pKa for the deprotonation of carboxylic acids?
5.
What is the pKa for the deprotonation of phenols?
10.
What is the pKa for the deprotonation of alcohols?
15.
