The crystal structure of the title compound, C 6 H 5 NO 2 , has been redetermined to confirm that the space group C2/c is correct for the averaged structure in time and space. A zigzag chain is formed by the hydrogen bonds, N-H···N and O-H···O, and these protons are disordered around the twofold axis or the center of symmetry. The solid state high resolution 15 N-CP/ MAS NMR spectrum clearly revealed the two separate signals of protonated and nonprotonated N atoms. It was concluded that the intermolecular N-H···N hydrogen bond is asymmetric and hydrogen atom is trapped at one of the two nitrogen atoms. However, there is a crystallographic twofold axis through the mid point of the N···N bond. These facts indicate that the neutral molecules and zwitter ions are arranged alternately at local domains in the NMR time scale. ExperimentalBoth single and twin crystals were grown from the benzene/ethyl acetate (1:1) solution. They could easily be distinguished from their crystal habits. RefinementThe crystal structure is essentially the same with that reported by Takusagawa and Shimada (1973). The H2 and H3 atoms, which are involved in the intermolecular hydrogen bonds, O2-H2···O2 (2 − x, 1 − y, 1 − z) and N3-H3···N3 (2 − x, y, 1/2 − z), show positional disorder. There are two possible positions both for H2 and H3, which are related by center of symmetry or twofold axis, and their site occupation factors were assumed to be 50%. The positional and isotropic thermal parameters of H2 and H3 were refined. The positions of H atoms bonded to C were calculated geometrically, and a riding model was used in their refinement [C-H 0.96 Å, U iso (H)=0.05 Å 2 ]. Computing detailsData collection: AFC/MSC Diffractometer Control System (Rigaku Corporation, 1993); cell refinement: AFC/MSC Diffractometer Control System; data reduction: local programs; program(s) used to solve structure: CRYSTANGM (Edwards et al., 1996); program(s) used to refine structure: CRYSTANGM; molecular graphics: CRYSTANGM; software used to prepare material for publication: CRYSTANGM. 2-pyridinecarboxylic acidCrystal data C 6 H 5 N 1 O 2 V = 1084.0 (12) Å 3

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structure structure (organic substances) K 9000 -037(E)-o-Stilbenecarboxylic Acid and Its p-Methyl, -Chloro and -Methoxy Derivatives. -The crystal structures of title compounds (I) are determined. Bromination of carboxylic acid (Ia) in solution gives isocoumarin (IIa) as major product, whereas in solid state dibromo compound (IIIa) is generated selectively. Bromination of derivatives (Ib) and (Ic) in solid state gives only dibromo compounds (IIIb) and (IIIc), resp., but derivative (Id) gives mainly isocoumarin (IId). -(HAMAZAKI, H.; OHBA, S.; TODA, F.; TAKUMI, H.; Acta Crystallogr.