Chemical Education Today
Letters Phototropic Reaction I refer to the article Cornell College Students Achieve the Highly Improbable by A. Ault (J. Chem. Educ. 2000, 77, 1386–1387). The authors give a wrong interpretation for the interesting phototropic reaction. They have failed to study the relevant literature which should also be given as references, for example: Sixl, H.; Warta, R. Chem. Phys. 1985, 94, 147–155. Lehn, J.-M., et al. J. Phys. Chem. 1996, 100, 16175– 16186.
According to this, a hydrogen atom is transferred to the nitrogen atom of the pyridine ring and not to an oxygen atom of a nitro group. Paul Rademacher Institut für Organische Chemie Universität Essen, 45117 Essen, Germany
[email protected] The author replies: I thank Paul Rademacher for drawing my attention to recent publications that concern the structure of the blue substance that is produced by exposure of 2-(2,4dinitrobenzyl)pyridine to the light. Apparently, while exposure of the “CH” substance to light produces both the “OH” and “NH” substances, it is the “NH” material that is responsible for the blue color. O + O N H
H
−
H O + O N H
N
N
−
O H
+
H
O
−
N
N
CH brown sugar brown
OH
NH blue jeans blue
We could speculate that the deep blue color is a result of the effective resonance delocalization that is present in the NH form: O H
H
+
O
−
−
N
H
H
O
+
O
−
N
+
N
N
NH form Addison Ault Department of Chemistry Cornell College, Mount Vernon, IA 52314
[email protected] 1596
Journal of Chemical Education • Vol. 78 No. 12 December 2001 • JChemEd.chem.wisc.edu
