Mukhopadhyay Anamika, Mukherjee Moitrayee, Pandey Prasenjit, Samanta Amit K, Bandyopadhyay Biman, Chakraborty Tapas
Department of Physical Chemistry and Raman Center for Atomic Molecular and Optical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India.
J Phys Chem A. 2009 Apr 2;113(13):3078-87. doi: 10.1021/jp900473w.
Blue-shifting C-H...O hydrogen bonded complexes between chloroform and three small cyclic ketones (cyclohexanone, cyclopentanone, and cyclobutanone) have been identified by use of FTIR spectroscopy in CCl(4) solution at room temperature. The shifts of the C-H stretching fundamental of chloroform (nu(C-H)) in the said three complexes are +1, +2, and +5 cm(-1), respectively, and the complexation results in enhancement of the nu(C-H) transition intensity in all three cases. The 1:1 stoichiometry of the complexes is suggested by identifying distinct isosbestic points between the carbonyl stretching (nu(C=O)) fundamentals of the monomers and corresponding complexes for spectra measured with different chloroform to ketone concentrations. The nu(C=O) bands in the three complexes are red-shifted by 8, 19, and 6 cm(-1), and apparently have no correlation with the respective blue shifts of the nu(C-H) bands. Spectral analysis reveals that the complex with cyclohexanone is most stable, and the stability decreases with the ring size of the cyclic ketones. A qualitative explanation of the relative stabilities of the complexes is presented by correlating the hydrogen bond acceptor abilities of the carbonyl groups with the ring size of the cyclic ketones. Quantum mechanical calculations at the DFT/B3LYP/6-311++G(d,p) and MP2/6-31+G(d) levels were performed for predictions of the shapes of the complexes, electronic structure parameters of C-H (donor) and C=O (acceptor) groups, intermolecular interaction energies, spectral shifts, and evolution of those properties when the hydrogen bond distance between the donor-acceptor moieties is scanned. The results show that the binding energies of the complexes are correlated with the dipole moments, proton affinity, and n(O) --> sigma*(C-H) hyperconjugative charge transfer abilities of the three ketones. NBO analysis reveals that the blue shifting of the nu(C-H) transition in a complex is the net effect of hyperconjugation and repolarization/rehybridization of the bond under the influence of the electric field of carbonyl oxygen.
在室温下的四氯化碳溶液中，利用傅里叶变换红外光谱法已鉴定出氯仿与三种小环酮（环己酮、环戊酮和环丁酮）之间形成的蓝移C-H...O氢键复合物。在上述三种复合物中，氯仿的C-H伸缩基频（ν(C-H)）的位移分别为+1、+2和+5 cm⁻¹，并且在所有三种情况下，络合作用都会导致ν(C-H)跃迁强度增强。通过识别单体的羰基伸缩（ν(C=O)）基频与不同氯仿与酮浓度下测量的光谱中相应复合物之间明显的等吸收点，表明复合物的化学计量比为1:1。三种复合物中的ν(C=O)带红移了8、19和6 cm⁻¹，并且显然与ν(C-H)带各自的蓝移没有相关性。光谱分析表明，与环己酮形成的复合物最稳定，并且稳定性随着环酮的环尺寸减小而降低。通过将羰基的氢键受体能力与环酮的环尺寸相关联，对复合物的相对稳定性进行了定性解释。在DFT/B3LYP/6-311++G(d,p)和MP2/6-31+G(d)水平上进行了量子力学计算，以预测复合物的形状、C-H（供体）和C=O（受体）基团的电子结构参数、分子间相互作用能、光谱位移以及当供体-受体部分之间的氢键距离被扫描时这些性质的演变。结果表明，复合物的结合能与三种酮的偶极矩、质子亲和力和n(O)→σ*(C-H)超共轭电荷转移能力相关。自然键轨道（NBO）分析表明，复合物中ν(C-H)跃迁的蓝移是超共轭以及在羰基氧电场影响下键的再极化/再杂化的净效应。
