Department of Physics, Banaras Hindu University, Varanasi, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2010 Jan;75(1):281-92. doi: 10.1016/j.saa.2009.10.025. Epub 2009 Oct 21.
FTIR spectra of nicotinamide and its N-oxide have been recorded and analyzed in the range 400-4000 cm(-1). The stabilities, optimized molecular geometries, APT charges and vibrational characteristics for the two possible conformers of nicotinamide and its N-oxide have been studied theoretically using restricted Hartree-Fock (RHF) and density functional theory (DFT) methods. The E (trans) conformers of nicotinamide and its N-oxide are found to be more stable and less polar than their respective Z (cis) conformers. Due to addition of an O atom at the N(1) site in the NA molecule the magnitudes of atomic charges on all the H atomic sites are found to increase. For all the studied molecules, magnitude of the wagging mode of the NH(2) group is found to be higher than its torsion mode, which is in the reverse order as compared to that for the aniline molecule. Most of the vibrational frequencies have nearly the same magnitude for the two conformers of nicotinamide and its N-oxide, however, significant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands. The frequency of the ring breathing mode for the NA molecule is found to decrease by 100 cm(-1) in going to the NANO molecule for both the conformers. The IR intensity for the scissoring mode of the CON(H(2)) group is found to decrease significantly for the NA-II conformer as compared to that for the NA-I conformer.
已记录并分析了烟酰胺及其 N-氧化物在 400-4000 cm(-1) 范围内的傅里叶变换红外（FTIR）光谱。使用受限哈特利-福克（RHF）和密度泛函理论（DFT）方法研究了烟酰胺及其 N-氧化物两种可能构象的稳定性、优化分子几何形状、APT 电荷和振动特性。发现烟酰胺及其 N-氧化物的 E（反式）构象比其各自的 Z（顺式）构象更稳定且极性更小。由于在 NA 分子的 N(1)位添加了一个 O 原子，所有 H 原子位置的原子电荷值都增大。对于所有研究的分子，NH(2)基团的摇摆模式的幅度都高于其扭转模式，这与苯胺分子的顺序相反。对于烟酰胺及其 N-氧化物的两种构象，大多数振动频率的大小几乎相同，但是它们的红外强度、拉曼活性和拉曼带的退偏比发生了明显变化。对于两种构象，NA 分子的环呼吸模式的频率都降低了 100 cm(-1)，在 NANO 分子中。与 NA-I 构象相比，CON(H(2))基团的剪切模式的红外强度对于 NA-II 构象显著降低。
