In the title compound, C(17)H(20)FN(3)O(3)·6H(2)O, the pefloxacin (pef) neutral zwitterion is accompanied by six water mol-ecules of hydration. An extensive network of O-H⋯O and N-H⋯O hydrogen bonds help to establish the crystal packing.

The title compound, C(9)H(10)N(2)O(4)·H(2)O, exists as a zwitterion with a deprotonated carboxyl group and a protonated amine group. The crystal packing is stabilized by inter-molecular N-H⋯O and O-H⋯O hydrogen bonds, building sheets parallel to the (001) plane.

In the crystal structure of the title compound, C(3)H(8)N(2)O(2)·H(2)O, the organic mol-ecule exists as zwitterion with the carboxyl group deprotonated and the amino group protonated. In the crystal, the components are linked by O-H⋯O and N-H⋯O hydrogen bonds.

The title γ-amino-butyric acid, C(7)H(13)NO(2), exists as a zwitterion. The crystal structure is stabilized by a network of inter-molecular N-H⋯O hydrogen bonds, forming a two-dimensional bilayer. An inter-molecular C-H⋯O hydrogen bond is also observed.

Reaction of the -CH2OSiMe3 substituted allyldimesitylphosphane 5 with HB(C6F5)2 resulted in a hydroboration/(C6F5)2BOSiMe3 elimination sequence to give the phosphinomethyl substituted cyclopropane derivative , probably via a phosphiranium type intermediate. Addition of B(C6F5)3 to compound gave the stable phosphiranium/borate zwitterion that was isolated and characterized by X-ray diffraction.

The phosphonium borane [p-Mes(2)B(C(6)H(4))PMePh(2)](+) complexes fluoride in water containing 10% methanol with a binding constant of 1.0(+/-0.1) x 10(3) M(-1) to afford the zwitterion p-Mes(2)FB(C(6)H(4))PMePh(2).

The title compound, C(7)H(8)N(2)O(4), crystallizes as a zwitterion, with mol-ecules organized into mol-ecular sheets via carbox-yl-carboxyl-ate and N(+)-H⋯carboxyl-ate contacts. These sheets are constructed from translationally related mol-ecules that further link to neighboring motifs via π-stacking [centroid-centroid distance 3.504 (3) Å] and weak C-H⋯O contacts.

Six 3-methylpyridine zwitterions and six quinoline zwitterions were synthesized through the reaction of 4-hydroxycoumarins, p-benzoquinone and the corresponding N-aromatics. The novel pseudo-cyclic face-to-face rigid structure of the zwitterion was elucidated by (1)H-NMR at different temperatures, and assumed to be caused by both the intramolecular ion pair attraction and the steric interaction.

The title compound, C(16)H(20)NO(4)P, crystallizes as a zwitterion. In the mol-ecule, the two aromatic rings form a dihedral angle of 55.2 (1)°. In the crystal, inter-molecular N-H⋯O and O-H⋯O hydrogen bonds link the mol-ecules into columns propagating in [010].

The title compound, C(7)H(11)NO(7)P(2), exists as a zwitterion in which the positive charge resides on the protonated pyridyl N atom and the negative charge on one of the two phosphate groups. In the crystal, adjacent molcules are linked by O-H⋯O and N-H⋯O hydrogen bonds into a three-dimensional network.