PHYSICAL CHEMISTRY REVISION QUESTIONS 2024/2025. THE LATEST
REVISION QUESTIONS AND CORRECT ANSWERS IN 2024/2025. (ALREADY
GRADED A+) (LATEST 2024 UPDATE)
What are the selection rules for rotational spectroscopy? - ANSWER- The molecule must
possess a permanent dipole
∆J = ±1
What is the gross and specific selection rule for vibrational spectroscopy? - ANSWER- Gross:
there must be a change in dipole moment of the molecule during the vibration
Specific: ∆v = ±1
The frequency of oscillation is given by: - ANSWER- ν = 1/2π(kf/μ)^1/2
kf = force constant (N m-1)
What is the equation for the energy of the vth
energy level? - ANSWER- Ev = (v + 0.5)hν
v = vibrational quantium number
ν = frequency of oscillation
How many vibrational nodes does a linear molecule have? - ANSWER- 3N - 5
How many vibrational nodes does a non-linear molecule have? - ANSWER- 3N - 6
What are the types of vibrational modes? (6) - ANSWER- symmetrical stretch, asymmetrical
stretch, wagging, twisting, rocking, scissoring
What is vibrational spectroscopy also known as? - ANSWER- Infra-red spectroscopy
, What happens to the LUMO-HOMO gap when conjugation increases - ANSWER- it decreases
What is the Zeeman effect? - ANSWER- In the absence of a magnetic field the two spin levels
have the same energy
If a magnetic field is applied then the levels split depending on whether the *spin lines up with or
against the magnetic field direction*
Higher shielding causes a higher or lower chemical shift? NMR - ANSWER- lower chemical
shift
How do hydrogen atoms effect shielding? NMR - ANSWER- The more hydrogen atoms on a
carbon the greater the shielding
How do adjacent electronegative atoms effect shielding? NMR - ANSWER- Decreases
shielding
How does unsaturation effect shielding? NMR - ANSWER- Decreases shielding
How do you work out the number of nuclei giving rise to a particular signal? - ANSWER- The
area under the signal is proportional to the number
gives a ratio of H atoms for each peak
What is coupling caused by in C13 NMR? - ANSWER- the H nuclei on the same carbon atom
(the adjacent C is too far away to have an effect)
What is coupling caused by in H NMR? - ANSWER- the H on adjacent C atoms
REVISION QUESTIONS AND CORRECT ANSWERS IN 2024/2025. (ALREADY
GRADED A+) (LATEST 2024 UPDATE)
What are the selection rules for rotational spectroscopy? - ANSWER- The molecule must
possess a permanent dipole
∆J = ±1
What is the gross and specific selection rule for vibrational spectroscopy? - ANSWER- Gross:
there must be a change in dipole moment of the molecule during the vibration
Specific: ∆v = ±1
The frequency of oscillation is given by: - ANSWER- ν = 1/2π(kf/μ)^1/2
kf = force constant (N m-1)
What is the equation for the energy of the vth
energy level? - ANSWER- Ev = (v + 0.5)hν
v = vibrational quantium number
ν = frequency of oscillation
How many vibrational nodes does a linear molecule have? - ANSWER- 3N - 5
How many vibrational nodes does a non-linear molecule have? - ANSWER- 3N - 6
What are the types of vibrational modes? (6) - ANSWER- symmetrical stretch, asymmetrical
stretch, wagging, twisting, rocking, scissoring
What is vibrational spectroscopy also known as? - ANSWER- Infra-red spectroscopy
, What happens to the LUMO-HOMO gap when conjugation increases - ANSWER- it decreases
What is the Zeeman effect? - ANSWER- In the absence of a magnetic field the two spin levels
have the same energy
If a magnetic field is applied then the levels split depending on whether the *spin lines up with or
against the magnetic field direction*
Higher shielding causes a higher or lower chemical shift? NMR - ANSWER- lower chemical
shift
How do hydrogen atoms effect shielding? NMR - ANSWER- The more hydrogen atoms on a
carbon the greater the shielding
How do adjacent electronegative atoms effect shielding? NMR - ANSWER- Decreases
shielding
How does unsaturation effect shielding? NMR - ANSWER- Decreases shielding
How do you work out the number of nuclei giving rise to a particular signal? - ANSWER- The
area under the signal is proportional to the number
gives a ratio of H atoms for each peak
What is coupling caused by in C13 NMR? - ANSWER- the H nuclei on the same carbon atom
(the adjacent C is too far away to have an effect)
What is coupling caused by in H NMR? - ANSWER- the H on adjacent C atoms
