Spectroscopy Mock Tests

In the IR spectrum of acetone (CH₃COCH₃), which of the following characteristic absorptions would you expect to observe?

The rotational spectrum of a diatomic molecule shows equally spaced lines separated by 20 cm⁻¹. What is the rotational constant B of the molecule?

The number of IR-active vibrational modes of CO₂ in the linear geometry is:

The ¹H NMR spectrum of ethanol (CH₃CH₂OH) recorded at room temperature in a pure sample (without D₂O exchange) shows how many signals and what splitting pattern for the CH₂ protons, respectively?

In the ¹H NMR spectrum of acetone (CH₃COCH₃) recorded in CDCl₃, how many signals are observed and what is the approximate chemical shift (δ) of the signal(s)? (Consider only the protons directly attached to carbon atoms, excluding any exchangeable protons.)

The UV-Vis absorption spectrum of the permanganate ion (MnO₄⁻, tetrahedral, T_d symmetry) shows an intense purple colour with a molar absorptivity ε ≈ 2000 L/(mol·cm) at approximately 525 nm. This absorption band is due to which type of electronic transition? (Mn is in the +7 oxidation state with d⁰ configuration. The T_d point group has no centre of inversion. The valence electrons reside in oxygen-based ligand orbitals, and the lowest energy transitions involve charge transfer from oxygen p orbitals to empty manganese d orbitals.)

In the ¹H NMR spectrum of ethanol (CH₃CH₂OH) recorded at room temperature in a non-polar solvent, the signal for the OH proton appears as:

The fundamental vibrational wavenumber of the ¹²C¹⁶O molecule is 2143 cm⁻¹. Assuming the C−O bond can be modelled as a harmonic oscillator, what is the force constant k of the C−O bond? (Use the relation: ν̃ = (1/(2πc)) × √(k/μ), where μ is the reduced mass and c = 3 × 10¹⁰ cm/s. The atomic masses are: ¹²C = 12.000 amu, ¹⁶O = 15.995 amu, and 1 amu = 1.6605 × 10⁻²⁷ kg.)