Subjects

Inorganic Chemistry · f Block Lanthanides: The Contraction and Why Separation Is So Hard One structural fact — poor shielding by f electrons — explains the contraction, the similarity of the elements, and the difficulty of separating them. BSc & MSc · Inorganic Chemistry · Concept The short answer: Across the lanthanide series the 4f electrons shield the nuclear charge poorly, so the effective nuclear charge rises steadily and the ionic radius falls. That contraction makes the elements chemically almost identical, which is why they occur together and separating them requires methods exploiting very small differences. What the contraction is…

Protecting Groups: When to Use One and How to Choose

September 7, 2026

| Chemical Science Exams, Organic Chemistry

Organic Chemistry · Synthesis Protecting Groups: When to Use One and How to Choose A synthesis question that looks impossible usually becomes routine once you notice which group needs protecting. BSc & MSc · Organic Chemistry · Method The short answer: A protecting group temporarily converts a reactive functional group into an unreactive one so a reaction can be performed elsewhere. It must go on selectively, survive the intended reaction, and come off under conditions the rest of the molecule tolerates. Failing any of those three makes it useless. The problem being solved Most reagents are not perfectly selective. A…

Vibrational Spectroscopy: Force Constants and Anharmonicity

September 7, 2026

Physical Chemistry · Spectroscopy Vibrational Spectroscopy: Force Constants and Anharmonicity The harmonic oscillator explains where the band is. Anharmonicity explains everything the harmonic model gets wrong, including why molecules can dissociate at all. BSc & MSc · Spectroscopy · Concept The short answer: A vibrating bond behaves approximately as a harmonic oscillator with evenly spaced levels and a selection rule of one quantum. The frequency depends on the force constant and the reduced mass, so a stiffer bond or lighter atoms absorb at higher wavenumber. Real bonds are anharmonic, which produces converging levels and permits overtones. The harmonic oscillator Model…

Rotational Spectroscopy: Measuring a Bond Length From a Spectrum

September 6, 2026

Physical Chemistry · Spectroscopy Rotational Spectroscopy: Measuring a Bond Length From a Spectrum Line spacing gives the rotational constant, the rotational constant gives the moment of inertia, and that gives the bond length. Three steps, no ambiguity. BSc & MSc · Spectroscopy · Method The short answer: For a rigid diatomic rotor the energy levels are E = BJ(J+1), so successive transitions are separated by exactly 2B. Measure that spacing, extract B, convert to the moment of inertia and then to the bond length. The whole chain rests on the selection rule that J changes by one. The rigid rotor…

Carbohydrate Structure: Anomers, Mutarotation and Ring Forms

September 6, 2026

| Chemical Science Exams, Organic Chemistry

Organic Chemistry · Biomolecules Carbohydrate Structure: Anomers, Mutarotation and Ring Forms Most carbohydrate confusion comes from moving between the open-chain and cyclic representations. Fix that and the chemistry is straightforward. BSc & MSc · Organic Chemistry · Concept The short answer: A sugar cyclises when its own hydroxyl attacks its carbonyl, forming a hemiacetal and creating a new stereocentre at that carbon — the anomeric centre. The two configurations are anomers, and in solution they interconvert through the open-chain form, which is what mutarotation measures. Open chain to ring A monosaccharide contains a carbonyl and several hydroxyls. One hydroxyl, positioned…

Boranes and Wade’s Rules: Predicting Cluster Shapes

September 6, 2026

Inorganic Chemistry · Main Group Boranes and Wade’s Rules: Predicting Cluster Shapes Boron clusters look chaotic until you count skeletal electron pairs. Then each structure follows from a single number. BSc & MSc · Inorganic Chemistry · Method The short answer: Count the skeletal electron pairs. For n boron vertices, n+1 pairs gives a closo structure, n+2 gives nido, n+3 gives arachno. Each type is derived from the closo polyhedron by removing vertices, so the shapes are related rather than independent. Why boranes need special treatment Boron has three valence electrons but four valence orbitals, so it cannot form enough…

Michaelis–Menten Enzyme Kinetics: Derivation and Interpretation

September 6, 2026

Physical Chemistry · Kinetics Michaelis–Menten Enzyme Kinetics: Derivation and Interpretation A steady-state derivation applied to a biological catalyst, giving two constants whose meanings are constantly confused. BSc & MSc · Physical Chemistry · Concept The short answer: Apply the steady-state approximation to the enzyme–substrate complex and the rate becomes v = Vmax[S]/(KM + [S]). KM is the substrate concentration at half maximal rate and indicates how tightly the substrate binds; Vmax reflects how fast the enzyme turns over once saturated. The mechanism E + S ⇌ ES (k1 forward, k−1 reverse) ES → E + P (k2) The enzyme…

Stability Constants and the Chelate Effect

September 5, 2026

Inorganic Chemistry · Coordination Stability Constants and the Chelate Effect Why a ligand that bites twice binds far more tightly than two ligands that bite once — and why the answer is entropy, not bond strength. BSc & MSc · Inorganic Chemistry · Concept The short answer: Complex formation proceeds stepwise, each step with its own constant, and the overall constant is their product. Chelating ligands give far larger overall constants than comparable monodentate ligands. The dominant reason is entropic: one chelate molecule replaces several monodentate ones, increasing the number of free particles. Stepwise and overall constants Ligands add one…

The Phase Rule and Reading Phase Diagrams

September 5, 2026

Physical Chemistry · Equilibria The Phase Rule and Reading Phase Diagrams One short equation that tells you how many variables you are free to change, and a diagram that shows the consequence. BSc & MSc · Physical Chemistry · Concept The short answer: The phase rule states F = C − P + 2, where F is the degrees of freedom, C the number of components and P the number of phases in equilibrium. Applied to a one-component diagram it explains why an area has two degrees of freedom, a line one, and the triple point none. The rule F…

Electron Transfer: Inner Sphere versus Outer Sphere

September 5, 2026