The CN radical (cyano radical) is paramagnetic. It has 13 electrons, and one of them is unpaired, which gives the molecule a net magnetic moment that is attracted to external magnetic fields.
Why CN Is Paramagnetic
Whether a molecule is paramagnetic or diamagnetic comes down to one thing: unpaired electrons. If every electron is paired, the molecule is diamagnetic and weakly repelled by a magnetic field. If even one electron is unpaired, the molecule is paramagnetic and attracted to a magnetic field. CN has one unpaired electron, making it paramagnetic.
To see where that unpaired electron comes from, you need to look at how CN’s 13 electrons fill its molecular orbitals. Carbon contributes 6 electrons and nitrogen contributes 7. When you build the molecular orbital diagram, the filling order is: σ(1s), σ*(1s), σ(2s), σ*(2s), π(2p), σ(2p), π*(2p), σ*(2p). The first 12 electrons fill orbitals in pairs through the two degenerate π(2p) orbitals. The 13th electron goes alone into the σ(2p) bonding orbital. That lone electron is the source of CN’s paramagnetism.
Where the Unpaired Electron Sits
The unpaired electron in CN isn’t shared equally between the two atoms. Research published in The Journal of Physical Chemistry A found that in its ground state, the unpaired electron is hosted primarily on the carbon atom. This is somewhat counterintuitive since nitrogen is the more electronegative atom, but the molecular orbital that holds the 13th electron has a larger contribution from carbon. Interestingly, the carbon atom also bears the positive end of the molecule’s dipole moment (1.45 D), meaning the bonding electrons are pulled toward nitrogen while the lone unpaired electron stays on carbon.
Experimental Confirmation
The paramagnetism of CN isn’t just a prediction from orbital diagrams. It has been confirmed experimentally using Electron Paramagnetic Resonance (EPR) spectroscopy, a technique that specifically detects unpaired electrons. EPR studies on CN radicals trapped in noble gas matrices at very low temperatures (around 7 K) have directly observed the signal produced by the unpaired electron. These experiments, along with earlier EPR work on the radiolysis of solid hydrogen cyanide at 77 K, consistently detect CN as a paramagnetic species.
The ground state of CN is formally designated ²Σ⁺ by spectroscopists. The superscript “2” is the spin multiplicity, calculated as 2S + 1, where S is the total spin quantum number. A multiplicity of 2 means S = 1/2, which corresponds to exactly one unpaired electron. NIST lists this as the confirmed ground state, consistent with the molecular orbital picture.
How CN Compares to CN⁻
This is where many students get tripped up. The cyanide ion, CN⁻, has 14 electrons instead of 13. That extra electron fills the σ(2p) orbital, pairing with the previously unpaired electron. With all electrons now in pairs, CN⁻ is diamagnetic. So the neutral radical CN and the common cyanide ion CN⁻ have opposite magnetic behavior, despite differing by just one electron.
The positively charged species CN⁺ has 12 electrons. All 12 fill orbitals in pairs, so CN⁺ is also diamagnetic. Of the three species, only the neutral CN radical is paramagnetic.
Why CN Exists as a Radical
A molecule with an unpaired electron is called a radical, and radicals are generally reactive. CN is no exception. It is commonly produced through the breakdown of hydrogen cyanide (HCN) by radiation or high temperatures, and it appears in interstellar chemistry, combustion environments, and laboratory plasma experiments. Its reactivity is driven by that same unpaired electron on carbon, which readily forms bonds with other atoms or molecules. In most stable chemical compounds, cyanide appears as the CN⁻ ion rather than the neutral radical, precisely because gaining one electron eliminates the unpaired spin and reaches a more stable, diamagnetic configuration.