Lasers and Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2011 Dec 15;84(1):6-21. doi: 10.1016/j.saa.2011.07.043. Epub 2011 Aug 2.
IR and spectra of the L-ascorbic acid (L-AA) also known as vitamin C have been recorded in the region 4000-50 cm(-1). In order to make vibrational assignments of the observed IR and Raman bands computations were carried out by employing the RHF and DFT methods to calculate the molecular geometries and harmonic vibrational frequencies along with other related parameters for the neutral L-AA and its singly charged anionic (L-AA(-)) and cationic (L-AA(+)) species. Significant changes have been found for different characteristics of a number of vibrational modes. The four ν(O-H) modes of the L-AA molecule are found in the order ν(O(9)-H(10))>ν(O(19)-H(20))>ν(O(7)-H(8))>ν(O(14)-H(15)) which could be due to complexity of hydrogen bonding in the lactone ring and the side chain. The CO stretching wavenumber (ν(46)) decreases by 151 cm(-1) in going from the neutral to the anionic species whereas it increases by 151 cm(-1) in going from the anionic to the cationic species. The anionic radicals have less kinetic stabilities and high chemical reactivity as compared to the neutral molecule. It is found that the cationic radical of L-AA is kinetically least stable and chemically most reactive as compared to its neutral and anionic species.
L-抗坏血酸（L-AA），又称维生素 C，其红外和光谱在 4000-50cm^(-1) 范围内已被记录。为了对观察到的红外和拉曼带进行振动分配，我们采用 RHF 和 DFT 方法计算了分子几何形状和简谐振动频率，以及中性 L-AA 及其单电荷阴离子（L-AA(-)）和阳离子（L-AA(+)）物种的其他相关参数。对于许多振动模式的不同特征，我们发现了显著的变化。L-AA 分子的四个 ν(O-H)模式按 ν(O(9)-H(10))>ν(O(19)-H(20))>ν(O(7)-H(8))>ν(O(14)-H(15))的顺序排列，这可能是由于内酯环和侧链中氢键的复杂性。从中性到阴离子物种时，CO 伸缩振动频率（ν(46)）降低了 151cm^(-1)，而从阴离子到阳离子物种时，它增加了 151cm^(-1)。阴离子自由基的动力学稳定性较低，化学活性较高，与中性分子相比。与中性和阴离子物种相比，我们发现 L-AA 的阳离子自由基在动力学上最不稳定，在化学上最具反应性。
