Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
J Phys Chem A. 2013 Feb 21;117(7):1651-8. doi: 10.1021/jp3117038. Epub 2013 Feb 7.
(14)N nuclear quadrupole resonance frequencies have been measured in solid 2-pyridone, 3-hydroxypyridine, and 4-pyridone by (1)H-(14)N nuclear quadrupole double resonance. Two slightly nonequivalent nitrogen positions are observed in solid 3-hydroxypyridine, whereas only one nitrogen position has been observed in 2-pyridone and 4-pyridone within the experimental resolution. Rather low (14)N quadrupole coupling constants in pyridones are the consequence of the delocalization of the nitrogen lone pair electrons in the aromatic rings. Two different compounds have been obtained by crystallization of 4-pyridone from ethanol in a normal and in a dry atmosphere. The compound obtained in the dry atmosphere is identical to the commercial sample. The compound obtained in the normal atmosphere cannot be converted to the commercial polymorph by melting. It is thus not a polymorph of anhydrous 4-pyridone. The temperature coefficient of the (14)N quadrupole coupling constant is negative in 3-hydroxypyridine and positive in 2- and 4-pyridone. Therefore, in 3-hydroxypyridine, molecular librations dominate the temperature variation of the quadrupole coupling constant, whereas in 2- and 4-pyridone, the changes in the hydrogen bonding interactions with temperature seem to give the dominant effect.
（14）N 核四极共振频率已通过（1）H-（14）N 核四极双共振在固体 2-吡啶酮、3-羟基吡啶和 4-吡啶酮中进行了测量。在固体 3-羟基吡啶中观察到两个稍微不等价的氮位置，而在 2-吡啶酮和 4-吡啶酮中，在实验分辨率范围内仅观察到一个氮位置。吡啶酮中相当低的（14）N 核四极耦合常数是由于氮孤对电子在芳香环中的离域化所致。通过在正常和干燥气氛中从乙醇中结晶 4-吡啶酮获得了两种不同的化合物。在干燥气氛中获得的化合物与商业样品相同。在正常气氛中获得的化合物不能通过熔融转化为商业多晶型物。因此，它不是无水 4-吡啶酮的多晶型物。在 3-羟基吡啶中，（14）N 核四极耦合常数的温度系数为负，而在 2-和 4-吡啶酮中为正。因此，在 3-羟基吡啶中，分子摆动主导着核四极耦合常数随温度的变化，而在 2-和 4-吡啶酮中，氢键相互作用随温度的变化似乎起着主导作用。
