throughbond

Throughbond is a term used in chemistry to describe the transmission of chemical influence or electronic information along covalent bonds within a molecule. It contrasts with through-space interactions, which act at a distance without bond mediation. Through-bond communication can refer to how substituent effects propagate along a molecular framework, affecting reactivity, acidity or basicity, and spectroscopic properties.

In organic chemistry, through-bond effects include inductive effects transmitted by sigma bonds and resonance or conjugation that delocalizes electrons along a system. The magnitude and reach of through-bond effects depend on bond types, geometry, and electronic structure. In aromatic systems, substituent constants such as Hammett sigma values quantify the through-bond transmission of electronic influence.

In spectroscopy, through-bond coupling describes spin–spin interactions detected as J-coupling in NMR that occur via bonds between nuclei. The coupling magnitude reflects the number of intervening bonds and bond angles, providing information about molecular connectivity and conformation.

In materials science and molecular electronics, through-bond transport refers to charge transfer or electron conduction along the backbone of a molecule or polymer, as opposed to tunneling through space or across weak supramolecular contacts. The efficiency depends on electronic coupling and the alignment of frontier molecular orbitals.

Limitations: the term is descriptive and context-dependent rather than a single formal theory; real systems often involve mixed through-bond and through-space contributions. See also through-space, J-coupling, inductive effect, resonance.