OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~648 words · 3 min

The 18-Electron Rule A transition-metal organometallic complex tends to be especially stable when its total valence electron count reaches 18 — filling the metal's nine valence orbitals (1 s + 3 p + 5 d), exactly as the octet rule fills 4 o

Chemistry

Chemistry · L5 · Organometallic Catalytic Cycles: The 18-Electron Rule in Action

@openstem

Note~789 words · 4 min

The Goal: Approximating the Schrödinger Equation A molecule's structure, energy, and most other properties are, in principle, all contained in the solution to its electronic Schrödinger equation: This equation can be solved exactly only for

Chemistry

Chemistry · L5 · Computational Chemistry & DFT Basics

@openstem

Note~1000 words · 5 min

Marcus Theory: Why and How Fast Electron Transfer Happens L4's electrochemistry note covered how far a redox reaction wants to go — E°cell and ΔG° = −nFE°cell tell you whether electrons will flow and how much useful work they can do. Marcus

Chemistry

Chemistry · L5 · Marcus Theory: Why and How Fast Electron Transfer Happens

@openstem

Note~1271 words · 6 min

Glass transition, crystallinity, and the chain-structure–property connection L4 classified polymers along one axis: how heavily are the chains cross-linked (thermoplastic vs elastomer vs thermoset)? This note works within the thermoplastics

Chemistry

Chemistry · L5 · Glass Transition, Crystallinity & Chain-Structure–Property Control

@openstem

Note~673 words · 3 min

Why Two Dimensions? A 1D ¹H spectrum plots intensity against a single chemical-shift axis. For a small molecule that is plenty — but for a molecule with many chemically similar protons, peaks pile up and overlap until individual multiplets

Chemistry

Chemistry · L5 · Advanced NMR: 2D Techniques & Coupling Analysis

@openstem

Note~417 words · 2 min

The Jablonski Diagram When a molecule absorbs a photon, an electron is promoted from the ground electronic state S₀ into some excited singlet state Sₙ (n ≥ 1) — often a higher singlet than S₁, since absorption is governed by whichever trans

Chemistry

Chemistry · L5 · Photochemistry: The Jablonski Diagram

@openstem

Note~589 words · 3 min

Chemistry Beyond the Molecule Jean-Marie Lehn coined 'supramolecular chemistry' to describe a field that sits one level up from ordinary synthesis: instead of building new covalent bonds inside a molecule, it studies how whole molecules and

Chemistry

Chemistry · L5 · Supramolecular Chemistry: Host–Guest Recognition & Preorganization

@openstem

Note~848 words · 4 min

Green chemistry — sustainable catalysis Atom economy tells you what a reaction could achieve on paper, from the balanced equation alone, before a single flask is ever run. The E-factor tells you what a process actually achieves — and the ga

Chemistry

Chemistry · L5 · Green Chemistry — Sustainable Catalysis: the E-factor, asymmetric catalysis, and green solvents

@openstem

Note~1236 words · 6 min

Enzyme kinetics: the Michaelis-Menten equation Enzyme catalysis is one of the richest, most consequential applications of the steady-state approximation you met for a generic two-step mechanism with an intermediate. There, a reactant A form

Chemistry

Chemistry · L5 · Enzyme Kinetics

@openstem

Note~1029 words · 5 min

Surface Chemistry and Adsorption: the Langmuir Isotherm You've already met several heterogeneous catalysts — iron in the Haber process, vanadium(V) oxide in the Contact process, and the platinum, palladium and rhodium of a catalytic convert

Chemistry

Chemistry · L5 · Surface Chemistry and Adsorption

@openstem

Note~924 words · 5 min

Statement of the Third Law The third law of thermodynamics states that the entropy of a perfect, pure crystalline substance approaches zero as the temperature approaches absolute zero: At 0 K, a perfect crystal has its particles locked into

Chemistry

Chemistry · L5 · The Third Law and Absolute Entropy

@openstem

Note~1029 words · 5 min

Crystal field stabilization energy: the arithmetic and its payoff Ligand field theory tells us how strong a given ligand's field is (the spectrochemical series) and whether a d⁴–d⁷ octahedral ion goes high-spin or low-spin. Crystal field st

Chemistry

Chemistry · L5 · Crystal Field Stabilization Energy: The Arithmetic and Its Payoff

@openstem

Note~1163 words · 6 min

Taming the randomness of chain growth Earlier polymer chemistry topics classified finished polymers by cross-link density and asked how chain structure sets bulk properties like Tg and crystallinity. This note steps back one stage further,

Chemistry

Chemistry · L5 · Controlled and Living Polymerization

@openstem

Note~930 words · 5 min

Asymmetric Catalysis Mechanisms Wilkinson's achiral hydrogenation cycle (RhCl(PPh3)3) already supplies the full mechanistic skeleton: ligand dissociation, oxidative addition, alkene association, migratory insertion, and reductive eliminatio

Chemistry

Chemistry · L5 · Asymmetric Catalysis Mechanisms: The Quadrant Model, Sharpless Epoxidation, and Organocatalysis

@openstem

Note~1027 words · 5 min

Crystal defects and semiconductors The unit-cell picture of a crystal — atoms sitting on perfectly regular lattice sites, with no gaps or extras — is an idealization. Real crystals almost always contain a small population of point defects:

Chemistry

Chemistry · L5 · Crystal Defects and Semiconductors

@openstem

Note~848 words · 4 min

Isotope Patterns: Reading M, M+1, and M+2 A mass spectrum's molecular-ion region is rarely a single clean peak. Small satellite peaks one and two mass units above M come from the natural abundance of heavier isotopes, and their heights are

Chemistry

Chemistry · L5 · Advanced Mass Spectrometry

@openstem

Note~1007 words · 5 min

Nanomaterials and quantum confinement A bulk semiconductor's band gap is fixed by its chemical composition and crystal structure — silicon's band gap is silicon's band gap, whether the sample is a millimeter or a meter across. That stops be

Chemistry

Chemistry · L5 · Nanomaterials and Quantum Confinement

@openstem

Note~761 words · 4 min

Chemiluminescence: The Opposite Starting Point Photochemistry starts with a photon going IN: a molecule absorbs light, is promoted to an excited electronic state, and eventually relaxes back down, sometimes emitting light of its own as fluo

Chemistry

Chemistry · L5 · Chemiluminescence: Light Out With No Light In

@openstem

Note~858 words · 4 min

The kinetic isotope effect: an experimental probe for the rate-determining step Identifying the rate-determining step of a proposed mechanism by argument alone — 'this step looks like the bottleneck' — or deriving a rate law from it algebra

Chemistry

Chemistry · L5 · The Kinetic Isotope Effect

@openstem

Note~793 words · 4 min

The CuAAC Reaction: A Third Kind of Cycloaddition The copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) joins an organic azide (R–N₃) and a terminal alkyne (R'–C≡CH) into a 1,2,3-triazole ring. Formally it is a [3+2] cycloaddition — th

Chemistry

Chemistry · L5 · Click Chemistry and Bioorthogonal Labeling

@openstem

Note~561 words · 3 min

Chirality Without a Stereocenter Ordinary (point) chirality requires a stereocenter: an atom bonded to four different substituents arranged tetrahedrally, whose mirror image cannot be superimposed on the original. Atropisomerism produces ch

Chemistry

Chemistry · L5 · Atropisomerism and Axial Chirality

@openstem

Note~548 words · 3 min

The Rocking-Chair Mechanism A lithium-ion battery does not consume its electrode materials the way, say, a lead-acid battery consumes lead and lead dioxide. Instead, Li⁺ ions shuttle back and forth between two intercalation host structures

Chemistry

Chemistry · L5 · Battery Chemistry & Materials

@openstem

Note~516 words · 3 min

Metalloenzymes: Nature's Small-Molecule Activation Chemistry A handful of metalloenzymes perform reactions — N2 fixation, four-electron water oxidation, selective C–H hydroxylation, reversible H2 cycling — that remain difficult or impossibl

Chemistry

Chemistry · L5 · Bioinorganic Metalloenzymes

@openstem

Note~593 words · 3 min

Six-Electron Carbon: Singlet and Triplet Carbenes A carbene carbon has only six valence electrons — two fewer than a normal tetravalent carbon — with two non-bonding electrons left over. Those two electrons can pair up in a single orbital (

Chemistry

Chemistry · L5 · Carbene Chemistry

@openstem

Note~614 words · 3 min

Measuring Activity, Not Just Abundance Most proteomic methods measure how much of a protein is present. Activity-based protein profiling (ABPP) instead measures whether an enzyme is catalytically FUNCTIONING, using a small-molecule probe de

Chemistry

Chemistry · L5 · Chemical Biology and Activity-Based Probes

@openstem

Note~542 words · 3 min

Docking: Fast Search, Approximate Scoring Molecular docking solves two problems together for every candidate compound: SEARCH (where and how does the ligand fit into the binding site — its pose) and SCORING (how favorable is that pose energ

Chemistry

Chemistry · L5 · Computational Docking & Drug Design

@openstem

Note~496 words · 2 min

Reading a Polarization Curve A fuel cell's polarization curve — cell voltage plotted against current density — always slopes downward from the theoretical open-circuit voltage, because drawing any real current incurs real voltage losses. Th

Chemistry

Chemistry · L5 · Electrocatalysis and Fuel Cells

@openstem

Note~458 words · 2 min

From Batch Flasks to Continuous Flow In batch chemistry, reagents combine in one vessel and the whole pool reacts together over an extended period, with heat and mass transfer limited by the flask's surface-to-volume ratio and the efficienc

Chemistry

Chemistry · L5 · Flow Chemistry and Continuous Processing

@openstem

Note~634 words · 3 min

A Label That (Mostly) Doesn't Change the Chemistry Isotopes of the same element share essentially identical electronic structure and chemical reactivity, differing mainly in nuclear mass and, for radioisotopes, decay behavior. That near-che

Chemistry

Chemistry · L5 · Isotope Labeling and Tracer Studies

@openstem

Note~554 words · 3 min

Buried Orbitals, Electrostatic Bonding The defining structural feature of lanthanide chemistry is that the 4f orbitals, despite carrying meaningful electron density close to the nucleus, are shielded from the surrounding ligand environment

Chemistry

Chemistry · L5 · Lanthanide and Actinide Chemistry

@openstem