molecular orbitals all ppqs to memorise Flashcards
Explain how a sigma bond is formed
End on overlap of (two atomic) orbitals
A pi bond is formed as a result of sp2 hybridisation.
.
Explain what is meant by sp2 hybridisation
Mixing an s (atomic) orbital with two p (atomic) orbitals
State the type of hybridisation which is adopted by the carbon atoms in the aromatic ring.
sp2
Describe how pi bonds form
Orbitals overlap sideways
Explain fully why a solution of the salt sodium 4-hydroxybenzoate
has a pH greater than 7.
The (4-hydroxybenzoate) ion from the salt removes/ reacts with H+ from the water
OR
Conjugate base of a weak acid, removes/reacts with H+ from the water (1)
This results in the water equilibrium shifting to the right hand side
Geometric isomers:
can occur when there is restricted rotation around a carbon-carbon double bond or a carbon-carbon single bond in a cyclic compound
must have two different groups attached to each of the carbon atoms that make up the bond with restricted rotation
can be labelled cis or trans according to whether the substituent groups are on the same side (cis) or on different sides (trans) of the bond with restricted rotation
State what is meant by the term optical isomers
Non-superimposable mirror images of each other
Explain fully how this conjugated system gives rise to the red colour of carmine.
Electrons promoted/move from HOMO to LUMO/ The complementary colour(s) (to red) is absorbed
Explain why methanol is a suitable solvent for this extraction.
Similar polarities
Optically active
Must have a chiral centre (4 different atoms attached)
State the structural feature present that is responsible for the colour of these dye molecules.
alternating double and single bonds.
Explain fully how colour arises in these dye molecules.
Electrons move from HOMO to LUMO. (1)
Absorption of light (from the visible part of the spectrum) means that light of the complementary colour is seen.
Explain fully why this dye molecule will absorb a shorter wavelength of light than the other two dye molecules.
There is less conjugation
Larger gap/greater energy absorbed
