The structure of 8-hydroxyquinoline-N-oxide was determined from diffractometer data by a direct method. The compound crystallizes in the monoclinic system with space group P21/c. The cell data are: a= 12.1364 (4), b=4.9211 (2), c= 13"1384 (4) /~, fl= I09"26 (1) °, Dealt= 1-449 g.cm -a, De,,p= 1.46 g.cm -3, Z= 4. The structure was solved by a direct method. A total of 1528 reflections were used in a full-matrix least-squares refinement. R was reduced to a final value of 0.053. Bond lengths between non-hydrogen atoms have e.s.d.'s between 0.002 and 0.003 A. The e.s.d.'s of the various bond angles (non-hydrogen atoms) range from 0"01 to 0"02 °. Distances and angles involving the hydrogen atoms have e.s.d.'s of 0.02/~ and 1 °, respectively. The two C-N distances of the quinoline ring are unusually long and the quinoline moiety is surprisingly similar to naphthalene in terms of bond distances and angles. It is believed that the inductive effect of the N-O group may in part be responsible for the C-N lengthenings. The hydroxyl hydrogen atom is bonded to the dative oxygen atom via a short intramolecular hydrogen bond. The direct relationship between the N-O dative bond distance and the strength of a hydrogen bond to the dative oxygen atom appears to be substantiated in this study.

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The structure of 2‐hydroxymethylpyridine N‐oxide was determined from X‐ray diffractometer data by a direct method. The compound crystallizes in the monoclinic space group P21/c with cell dimensions a = 7.079, b = 8.046, c = 10.599 Å, cosβ = −0.2252. A total of 1241 independent reflections were refined to an R value of 0.06. The N‐O dative bond has a length of 1.321 Å and the dative oxygen is bonded to a hydroxyl group on a symmetry related molecule by an inter‐molecular hydrogen bond. The structure corroborates recent findings concerning the relationship between the strength of hydrogen bonding to a dative oxygen and the length of the NO dative bond.