Benzene: 200 years of the molecule that shaped the 21st century

Exactly two centuries ago, in 1825, British scientist Michael Faraday identified a strange liquid by heating the gas residue used to light the streets of London. It was colorless, had a sweet, peculiar smell, and behaved in such a mysterious way that even the chemists of the time didn't quite know how to classify it. He called it hydrogen bicarbonate. No one imagined then that this substance, better known today as benzene, would change the history of science and our lives.

Today, the small molecule benzene is present in almost everything around us: plastics, dyes, detergents, textiles, perfumes, medicines , adhesives, fuels, insecticides, and even electronic devices like smartphones. But its influence goes beyond everyday products. Benzene's unique molecular structure has become the basis for thousands of organic compounds, with applications ranging from medicine to nanotechnology. Most impressively, the architecture of its atoms has led to the development of revolutionary materials like graphene, which promises to transform the future of energy, computing, and biomedicine.

The fascinating thing about benzene isn't just what it can be made from, but how it's made. Its molecule is composed of six carbon atoms and six hydrogen atoms, arranged in a ring. That small, perfect hexagon hides a chemical oddity: its electrons aren't fixed in single or double bonds—as in other organic molecules—but rather move continuously within the ring. This phenomenon is called electron resonance , and it gives benzene surprising stability.

It doesn't react easily, resists chemical attacks, and is also capable of forming new structures with great ease. This combination of reactivity and stability is what makes it so valuable. In chemistry, these properties are known as aromaticity , a term that originally referred to the smell of certain substances, but which today describes their unique electronic behavior.

The symbol of modern chemistry

Understanding these types of structures took decades of study. It was in the mid-19th century that German chemist August Kekulé proposed the model of the hexagonal ring with movable bonds, inspired—he said—by a dream in which a snake bit its tail. This event represented one of the great scientific milestones in the development of so-called structural theory. Since then, benzene has become the symbol of modern organic chemistry and a gateway to explaining more recent complex concepts such as molecular orbitals, electron delocalization, and molecular stability.

But their impact didn't stop at textbooks. As the 20th century progressed, scientists began joining several benzene rings together. This gave rise to polycyclic aromatic hydrocarbons (PAHs), compounds that are part of fuels, lubricating oils, dyes, and plastics, but also the subject of cutting-edge scientific research. Some PAHs have fluorescent properties, others function as semiconductors, and many served as the starting point for the development of new molecules with medical, electronic, and energy applications. These structures also gave rise to what are now known as molecular nanographenes, graphene fragments designed with atomic precision to function as sensors, transistors, or energy storage systems.

Graphene is, ultimately, the culmination of that evolution. It is a two-dimensional layer, just one atom thick, formed by a continuous network of carbon hexagons. It's like an infinite sheet made of benzene rings. Characterized in 2004 by Andre Geim and Konstantin Novoselov—who were awarded the Nobel Prize in Physics in 2010—graphene is extraordinary: it is the thinnest material ever created, stronger than steel, flexible, transparent, and with exceptional electrical and thermal conductivity. Its use is already being explored in ultra-fast batteries, foldable touchscreens, biomedical devices, water filtration systems, neural implants, and quantum technologies. Although it seems like something out of science fiction, graphene is a reality, and it all began with that tiny molecule behind the mysterious substance discovered by Faraday 200 years ago.

But benzene and its derivatives aren't just found in laboratories or factories: they also float in space. In recent decades, astronomers have detected aromatic compounds in interstellar clouds, comets, and the dusty disks surrounding young stars. These complex molecules, made up of benzene-like carbon rings, appear to be common in the universe and may have arrived on early Earth aboard meteorites. Their presence opens up a fascinating possibility: that the chemical building blocks of life—complex organic molecules—may have had a cosmic origin, with benzene as one of its earliest protagonists.

A scent of scientific revolution

It's curious how such a simple structure can have so many facets. Benzene is also a key molecule in chemistry teaching. Generations of students have learned concepts such as aromaticity, resonance, and molecular orbital theory from it. Despite its silent presence , it is a molecule that inspires wonder: for its perfect symmetry, its almost magical stability, and its ability to form complex compounds. And although it is also known that in high concentrations it can be toxic—which is why its use in household products has been limited and its presence in the environment is controlled—its scientific and technological legacy is unquestionable.

To celebrate this bicentenary, the Royal Society of Chemistry (RSC)—one of the world's most prestigious scientific institutions—will launch a special thematic issue featuring twenty of its journals, with articles dedicated to the history, evolution, and future of benzene and its derivatives. It will be coordinated by two leading figures in the field: Nobel Prize winner Ben Feringa and the author of this text. This special edition will cover everything from fascinating aromatic and antiaromatic compounds to benzene-based molecular machines, carbon nanotubes, fullerenes, and the new frontiers of graphene and its derivatives.

In times when technological innovation seems to be advancing at breakneck speed, in a world where we talk about artificial intelligence, messenger RNA vaccines, or satellites the size of a shoebox, it's worth remembering that many of these current wonders have their roots in discoveries of the past. Benzene, with its small molecule of six carbon atoms in the shape of a hexagonal ring, is one of those quiet discoveries that transformed our way of living, producing, healing, and creating. Sometimes, great revolutions don't arrive with a bang, but with a faint aroma and a perfect ring. And benzene, without a doubt, is one of them, a molecule whose aroma was synonymous with revolution from its very beginning.

Nazario Martín León is a professor of Organic Chemistry at the Complutense University, a National Research Award winner, and a member of the Royal Academy of Sciences.