concept

isomer

One of two or more compounds with the same formula but different arrangements of atoms.
22 related articles

Description

An isomer is one of two or more compounds that share the same molecular formula but differ in the arrangement of atoms, leading to distinct physical and chemical properties. This structural diversity is fundamental in chemistry, as isomers can have vastly different behaviors, from toxicity to reactivity. In astrophysics, isomers of molecules like hydrogen cyanide are found in interstellar space, where their relative abundances reveal the temperature and history of star-forming regions.

History

The concept was introduced in the 1830s by Jöns Jacob Berzelius, who coined the term 'isomerism' after observing that compounds like silver fulminate and silver cyanate had the same composition but different properties. The structural explanation came later with Kekulé and Couper in the 1850s.

How it works

Isomers arise because atoms can connect in different sequences (structural isomers) or adopt different spatial orientations (stereoisomers). The energy differences between isomers are often small, so external conditions like temperature or radiation can drive transitions. In space, the ratio of isomers is set by the local environment, acting as a thermometer or a probe of chemical pathways.

In practice

Isomer analysis is used in pharmaceutical development to ensure drug efficacy and safety, and in astrochemistry to interpret spectral lines from telescopes, revealing the conditions in molecular clouds.

Fun fact

Nuclear isomers, which are metastable states of atomic nuclei, can store energy for hours or even years, and their sudden decay can trigger powerful gamma-ray flashes, as observed in cosmic events.

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Related articles · 22

q-bio.SC2026-08-304 minarXiv:2608.29679
Ink Blots at the Cell Boundary: How Proteins Decide Where to Gather and Which Way to Look
Two ink reservoirs stand on opposite sides of the cell junction. From them, two types of monomers flow onto the membrane, and when they meet, they form viscous droplets of complexes. The droplets barely move, but the free monomers dart around as fast as perfume molecules in a room.
Chemical Physics2026-08-081 minarXiv:2608.08357express
How to Calculate Liquid Mixing at the Atomic Level
When sugar goes into tea, it dissolves. But why doesn't it just fall back out? It's all about chemical potential — a quantity that shows how 'favorable' it is for a substance to be in a given place and state. For a pure substance, it's easy to calculate, but for a mixture of several components, it's a real puzzle.
Exoplanets2026-07-212 minarXiv:2607.18683express
Chemical Portrait of a Young Star: When Infalling Gas Paints Patterns
The star AB Aur is young, about 4 million years old. Around it swirls a dense disk of gas and dust. Recently, a long gas stream, a flow of material from the surrounding cloud, crashed into it.
HEP Theory2026-07-081 minarXiv:2607.07684express
Cosmic Dimmer: From a Sharp Drop to Smooth Light
The early universe expanded at a breakneck pace: this phase is called inflation. But how exactly did it do it? Some models describe the expansion as a steep exponential surge, others as a more gentle power-law motion.
High Energy2026-06-242 minarXiv:2606.26447express
How Nuclear Isomers Give Themselves Away with Gamma Flashes
A collision of two neutron stars is a cosmic forge where the heaviest elements of the periodic table are hammered out in seconds. In 2017, detectors picked up gravitational waves from such a merger, and telescopes saw a flash — a kilonova.
Machine Learning2026-06-092 minarXiv:2606.11382express
Teaching Neural Networks to Read Molecules at a Glance
Finding the right molecule among billions of options is like finding a single grain in a sack of rice. To avoid sifting through everything by hand, chemists increasingly turn to neural networks. But large models require powerful computers, while small ones often lack the big picture. GLACIER tackles this problem like a bright student learning from several mentors at once.
Galaxies2026-06-022 minarXiv:2606.03313
Galaxies2026-05-082 minarXiv:2605.07159express
Glycine Isomer Found in Molecular Cloud Around Protostar
For nearly half a century, astronomers have been searching for glycine, the simplest amino acid and one of the fundamental building blocks of proteins, in the interstellar medium.
Galaxies2026-04-232 minarXiv:2604.21892express
How Invisible Hydrogen Is Rewriting the Chemistry of Space
A ball rolls up a hill, but it doesn't have enough energy, so it rolls back down. That's classical mechanics for you. But in the quantum world, a tiny particle can sometimes pass right through the hill, as if the barrier weren't there. This trick, tunneling, is business as usual for a light atom like hydrogen.
Galaxies2026-03-252 minarXiv:2603.24848express
Twin Molecules in Space
Every molecule is like a set of building blocks: the same pieces can be assembled in different ways. Two assemblies with the same atoms but different geometry are called isomers. If one can be turned into the other by a simple rotation around a bond, they are conformers, like a bent arm versus a straight one.
Galaxies2026-03-241 minarXiv:2603.23170express
Star Furnaces Don't Incinerate Life
Radio telescopes detected emissions from the celestial object G358.93-0.03 MM1 — a hot cocoon inside which a massive star is igniting. Within that glow, lines of glycolamide appeared, a delicate carbon molecule.
Exoplanets2026-03-201 minarXiv:2603.20445express
Interstellar Comet: Water 14 Times Heavier Than Earth's
Comet 3I/ATLAS was spotted when it entered the Solar System from interstellar space. The James Webb Telescope split the light from its gas cloud into a rainbow, a spectrum, and in this pattern, the lines of rare molecules with deuterium (heavy hydrogen) appeared.
Galaxies2026-02-231 minarXiv:2602.20241express
Chemistry Around Galaxies: What Their Outskirts Breathe
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Galaxies2026-02-051 minarXiv:2602.05383express
Cosmic Ice Holds Recipes for Molecules
In dark, cold clouds where stars are just beginning to form, dust grains put on icy coats. This ice is not just frozen water: it contains dissolved carbon dioxide, methanol, ammonia, and other molecules.
Galaxies2026-02-041 minarXiv:2602.04374express
How a Molecule with Sulfur and Nitrogen Is Born in Cosmic Ice
In the dark, cold clouds where stars are born, dust grains are covered with an icy crust. Across this crust, like on a winter road, individual atoms wander slowly. Calculations show that it is precisely these wandering oxygen and nitrogen atoms that kick off the assembly of the HNSO molecule — a compound of hydrogen, nitrogen, sulfur, and oxygen.
Quantum Physics2026-02-042 minarXiv:2602.04721express
Magnetic gridlock in a crowd of atoms
A crowd of people in a subway station moves slower than individuals: everyone gets in everyone else's way. A similar picture emerges in a dense cloud of magnetic atoms exchanging energy. Previously, it was thought that the transfer rate depended only on the atoms' own properties.
Galaxies2026-02-041 minarXiv:2602.04967express
Webb Reveals the Chemical Secret of a Distant Galaxy
Astronomers using James Webb and spectroscopy (splitting light into colors) peered through dust into the center of galaxy IRAS 07251-0248. There they discovered benzene, acetylene, methane — the same hydrocarbons found in gasoline and plastics.
Galaxies2026-01-121 minarXiv:2601.07162express
The Kitchen of Interstellar Carbon
In cold clouds of interstellar gas, carbon hides inside carbon monoxide (CO) molecules, like sugar dissolved in tea. But near hot, massive stars, this 'tea' boils: harsh radiation tears the molecules apart, and carbon escapes as lone atoms or ions.
Galaxies2026-01-091 minarXiv:2601.05507express
Alcohol in the Galaxy's Ice: What the Center of the Milky Way Hides
At the center of our Galaxy lies a dense forest of dust and gas. Starlight barely penetrates this thicket, like a flashlight in fog. But it is precisely there, in this dense cloud, that new stars are born. Scientists decided to look into this fog. They took light from 15 bright stars that shine through cold clouds.
Exoplanets2025-11-011 minarXiv:2511.00525express
How to Find Life: Look for Molecular Diversity
The chemical composition of a sample is like a soundscape. A living forest sounds polyphonic: chirping, rustles, the hum of insects. A barren desert is just the whistle of the wind.
Superconductivity2025-10-311 minarXiv:2511.00146express
Chimeric Materials: Magnetic Expulsion Without Superconductivity
Matter is like a house. In some rooms, there is the strict order of a crystal, where every atom is in its place. In others, the chaos of superfluid helium, where atoms forget about their neighbors.
Chameleon Crystal: How Six Ions Mimic Molecular Isomerization
Six barium ions lined up in a flat hexagon inside a Paul trap, a device that holds charged particles with oscillating electric fields. But a slight change in the shape of the trapping potential made the crystal rearrange: one ion moved to the center, and the other five formed a ring around it.