Nonzwitterionic

Nonzwitterionic refers to molecules that do not exist as zwitterions, i.e., they do not carry both a positive and a negative formal charge on different parts of the same molecule. In chemistry, zwitterions are species in which internal proton transfer creates distinct oppositely charged centers, often resulting in a net neutral charge. Nonzwitterionic compounds, by contrast, may be neutral without internal charge separation, or they may bear a net positive or net negative charge without forming a zwitterionic arrangement.

The designation is environment-dependent. A substance can be nonzwitterionic in one setting and zwitterionic in another, depending on factors such as pH, solvent polarity, and molecular structure. For example, amino acids commonly exist as zwitterions in aqueous solution near physiological pH, but under nonpolar conditions, in the gas phase, or at extreme pH, they can adopt nonzwitterionic forms in which the amino and carboxyl groups are not simultaneously charged.

Implications of nonzwitterionic character include differences in solubility, acid-base behavior, reactivity, and spectroscopic signature, as internal charge separation influences intermolecular interactions and crystal packing. In studies of amino acids and related compounds, recognizing whether a species is zwitterionic or nonzwitterionic helps interpret dissolution equilibria, crystallography results, and electrostatic properties.

The term is mostly descriptive and context-specific rather than a fixed property of a molecule. It is used to distinguish species that do not form internal charge-separated structures from true zwitterions.