heteronuclear

Heteronuclear is an adjective used in science to describe systems that are composed of unlike constituents. The term comes from Greek heteros meaning different and nucleus, and it is used across chemistry, physics, and related fields to contrast with homonuclear systems, which consist of identical constituents.

In chemistry, heteronuclear typically refers to molecules containing two or more different elements. A common example is a heteronuclear diatomic molecule, such as carbon monoxide (CO), hydrogen fluoride (HF), or nitric oxide (NO). These molecules generally exhibit a permanent electric dipole moment because the atoms have different electronegativities, leading to polar bonds. By contrast, homonuclear diatomic molecules like O2 or N2 have symmetric electron distributions and often lack a permanent dipole moment, which influences their spectroscopy and reactivity.

In spectroscopy and especially NMR, heteronuclear refers to nuclei other than the most abundant in a sample, typically 1H. Heteronuclear NMR experiments probe interactions between 1H and other nuclei such as 13C, 15N, or 19F, providing structural information through scalar (J) couplings. Techniques include HSQC and HMBC, which map heteronuclear correlations and assist in assigning atomic connectivities.

Beyond chemistry and NMR, heteronuclear concepts appear in fields such as astrochemistry, where models include heteronuclear diatomic molecules in interstellar environments, and in nuclear and particle physics where reactions involve different species of nuclei. In general, the term emphasizes the presence of unlike constituents rather than identical ones.