Subjects

Inorganic Chemistry · Solid State Solid State for Entrance Exams: Close Packing, Voids and Band Theory Solid state questions are almost always either a packing calculation or a conduction argument. Both are formula-driven once the structure is identified correctly. BSc & MSc · Inorganic Chemistry · Concept and numericals The short answer: Identify the lattice type first — simple cubic, body-centred or face-centred — because everything else follows from it: atoms per unit cell, coordination number, packing efficiency and the relationship between edge length and radius. Band theory then explains conduction as the gap between the filled and empty bands….

Aromaticity and Hückel’s Rule: Testing Any Ring in Four Steps

September 1, 2026

Organic Chemistry · Aromaticity Aromaticity and Hückel’s Rule: Testing Any Ring in Four Steps Aromaticity questions are answerable mechanically, but only if all four conditions are checked. Skipping the planarity test is where most wrong answers come from. BSc & MSc · Organic Chemistry · Concept The short answer: A ring is aromatic if it is cyclic, fully conjugated, planar, and contains 4n+2 π electrons in the delocalised system. All four conditions are necessary. A ring meeting the first three but holding 4n electrons is antiaromatic and destabilised; one that cannot achieve planarity is simply non-aromatic. The four conditions, all…

Maxwell Relations: Where They Come From and How to Use Them

August 31, 2026

| Chemical Science Exams, Physical Chemistry

Physical Chemistry · Thermodynamics Maxwell Relations: Where They Come From and How to Use Them Maxwell relations look like four formulas to memorise. They are actually one idea applied four times, and deriving them beats remembering them. BSc & MSc · Physical Chemistry · Concept The short answer: Each thermodynamic potential is an exact differential, so its mixed second derivatives are equal in either order. Applying that to U, H, A and G gives the four Maxwell relations. Their practical value is converting quantities that cannot be measured directly, such as an entropy derivative, into ones that can. The one…

Structure Determination by NMR: A Method That Works Every Time

August 31, 2026

Organic Chemistry · Spectroscopy Structure Determination by NMR: A Method That Works Every Time Structure problems reward a fixed procedure far more than chemical intuition. Follow the same order every time and the answer assembles itself. BSc & MSc · Spectroscopy · Method The short answer: Work out the degrees of unsaturation from the molecular formula first, then read integration for how many hydrogens, chemical shift for their environment, and multiplicity for their neighbours. Assemble fragments last. Candidates who guess a structure early and then try to justify it lose far more marks than those who build it piece by…

Pericyclic Reactions: Woodward–Hoffmann Rules Made Usable

August 31, 2026

Organic Chemistry · Pericyclic Pericyclic Reactions: Woodward–Hoffmann Rules Made Usable Pericyclic questions look intimidating and are actually among the most predictable on the paper, because the outcome follows from a rule table rather than from mechanism reasoning. BSc & MSc · Organic Chemistry · Concept The short answer: Count the electrons involved, note whether the reaction is thermal or photochemical, and read off the allowed mode. For electrocyclic reactions, 4n electrons go conrotatory under heat and disrotatory under light; 4n+2 electrons do the reverse. Everything else in the topic is an application of that pattern. What makes a reaction pericyclic…

The 18-Electron Rule and Hapticity: Counting Without Errors

August 30, 2026

Inorganic Chemistry · Organometallics The 18-Electron Rule and Hapticity: Counting Without Errors Electron counting is one of the few entrance-exam skills that is purely mechanical. Getting it wrong is almost always a bookkeeping slip, not a gap in understanding. BSc & MSc · Inorganic Chemistry · Method The short answer: Count the metal d electrons and add the electrons donated by each ligand. Eighteen corresponds to a filled valence shell and is the stable configuration for most low-oxidation-state transition metal complexes. Two counting conventions exist — ionic and neutral — and they give the same total provided you do not…

Crystal Field Theory: Splitting, CFSE and the Spectrochemical Series

August 30, 2026

Inorganic Chemistry · Coordination Crystal Field Theory: Splitting, CFSE and the Spectrochemical Series Coordination chemistry carries more entrance-exam weight than any other inorganic topic, and crystal field theory is the engine underneath most of it. BSc & MSc · Inorganic Chemistry · Concept The short answer: An octahedral field raises the two eg orbitals and lowers the three t2g orbitals, splitting them by Δo. Whether electrons pair up or occupy the upper set depends on whether Δo exceeds the pairing energy — which is what decides high-spin versus low-spin, and therefore colour, magnetism and stability. The model in one paragraph…

CIP Rules and R/S Assignment Without Mistakes

August 30, 2026

Organic Chemistry · Stereochemistry CIP Rules and R/S Assignment Without Mistakes Almost every stereochemistry error at entrance level comes from three specific places. Fix those and the assignments become mechanical. BSc & MSc · Organic Chemistry · Method The short answer: Rank the four groups on a stereocentre by atomic number at the first point of difference, put the lowest priority away from you, and read 1→2→3. Clockwise is R, anticlockwise is S. The rules are short; the errors come from exploring branches in the wrong order and from mishandling the case where the lowest group points toward the viewer….

Haemoglobin and Myoglobin: Coordination Chemistry Doing a Job

August 29, 2026