Geminal coupling is spin-spin coupling between two nuclei separated by two chemical bonds, commonly two hydrogens attached to the same carbon. It is denoted ${}^{2}J$ to distinguish it from a three-bond vicinal coupling.

Equivalent hydrogens do not split one another into separately observable multiplets in a simple first-order spectrum, even if a geminal interaction exists. Nonequivalent methylene hydrogens can show it clearly. The magnitude and sign depend on molecular structure and electronic environment, so the coupling is structural evidence rather than one fixed universal constant.

A nitrosyl shared between metal centres. In the simple mu2 counting model it contributes three electrons overall in the neutral method, or can be represented as an $\mathrm{N}{\mathrm{O}}^{-}$ donor of four electrons overall in ionic counting.

A near-linear M–N–O coordination mode conventionally represented as $\mathrm{N}{\mathrm{O}}^{+}$, a two-electron donor in ionic counting and a three-electron donor in neutral counting.

A bent M–N–O mode conventionally represented as $\mathrm{N}{\mathrm{O}}^{-}$, a two-electron ionic donor and a one-electron neutral donor. These are formal bookkeeping limits rather than measured atomic charges.

Nitrogen-15 is a stable isotope with seven protons and eight neutrons. Its nuclear spin is one-half, making it useful in isotope-labeling and nuclear-magnetic-resonance studies.

Replacing nitrogen-14 by nitrogen-15 changes mass and nuclear-spin properties while preserving closely related electronic chemistry. Enrichment can therefore make specific nitrogen-containing sites easier to observe in a complex biological molecule.

$\mathrm{PhC}\equiv \mathrm{N}$, the phenyl-substituted nitrile.

The Z isomer of $\mathrm{NCCH}=\mathrm{CHCN}$. A stereospecific Diels–Alder reaction retains the cis relationship between its two nitrile substituents.

A neural progenitor with radial processes and context-dependent neuronal or glial outputs. cell morphology, molecular state and traced descendants provide complementary evidence for its role.

Variation of absorption with incident electric-field direction. For a localized $1s\to {\pi }^{\ast }$ transition the dipole matrix element is proportional to the component of the field along the pi-orbital normal.

The minimum excludant of a finite set $S$ of nonnegative integers is the smallest nonnegative integer absent from $S$:For example, $\mathrm{mex}\{0,1,3\}=2$, while $\mathrm{mex}\varnothing =0$ and $\mathrm{mex}\{1,3\}=0$. It always exists and is at most $|S|$: the $|S|+1$ candidates $0,1,\dots ,|S|$ cannot all belong to a set of cardinality $|S|$.

In Sprague-Grundy theory, the Grundy number of a position in a finite acyclic impartial game is the mex of the values of its legal successor positions. The minimum excludant therefore converts the available moves into a reusable numerical description of a game position.

Growth by incorporation of dissolved individual atoms, ions or molecular units into a crystal, driven by supersaturation and limited by transport or attachment kinetics.

Joining of crystallites after compatible crystallographic alignment. Elimination of exposed interface drives the process; incomplete rotation and healing can leave defects.

Selection of unequal growth along otherwise equivalent directions, through defects, selective adsorption, kinetics or external asymmetry. A lower-symmetry shape need not imply a different bulk lattice.

Preferential adsorption of charged species onto particular crystal faces, reducing their normal incorporation rates. Both solution speciation and actual surface charge matter; crystallographic polarity alone does not fix adsorption selectivity.