采用密度泛函理论（DFT）B3LYP/6-311+G(d, p)及二级微扰理论（MP2）MP2/6-311G+(d, p)对3-呋喃甲酸单分子进行构型优化, 得到了该分子的两个稳定几何构型, 通过计算异构化反应的过渡态, 构型Ⅰ转变为构型Ⅱ要克服32.10 kJ·mol-1势垒, 异构化反应常温下较难进行。 玻尔兹曼分布结果表明常温下低能量的构型Ⅰ百分含量远高于高能量的构型Ⅱ, 故常温下以构型Ⅰ的形式存在。 在此基础上采用非谐性力场计算了单分子的红外光谱, 并计算了振动频率的势能分配比例, 指认了相应的振动模式, 发现单分子的计算数据与实际气相分子的红外谱图相似, 对2 000～2 500 cm-1出现的吸收峰可采用倍频、 和频给以解释。 对于二聚体, 采用考虑分子间弱相互作用校正的M06密度泛函进行模拟, 非谐性条件下二聚体的计算结果与固态谱图较为相符, 2 000～3 000 cm-1之间出现的弱吸收峰, 对应各种泛频峰, 经计算振动量子数对应的0→2红外跃迁的倍频吸收峰强度很小, 而基频之间形成的合频是造成这些峰的主因, 由于二聚体分子间是通过氢键而不是化学键结合的, 其刚性降低, 非谐性因素增大, 与之相关的合频峰的强度也随之增大, 在单体中不太明显的这些峰在二聚体中已很明显, 与实验谱图较为吻合。 但实际固体中由于存在多种二聚体、 多聚体, 使得羟基的红外吸收峰变宽且强度降低, 另外量子化学理论由于缺乏精准的弱相互作用的计算参数、 普适的力场、 合理的色散校正项等因素, 使得计算结果与实际谱图有一定差距。 进一步对该分子的二聚体进行了自然键轨道分析, 发现电子给体羰基氧原子与电子受体羟基形成的二级稳定化能为121.4 kJ·mol-1, 分子间结合能为65.27 kJ·mol-1, 给体反馈到受体轨道的电荷为0.067个电荷, 表明3-呋喃甲酸分子间的相互作用主要来自于形成的分子间氢键。 通过计算不同温度下二聚体的吉布斯自由能变, 当温度升高到500 K时ΔG值变为正值, 二聚体变得不稳定, 氢键被破坏, 单体分子将以分子间作用力结合在一起。

The single molecular configuration of 3-furoic acid was optimized using the density functional theory B3LYP/6-311G+(d,p) and the second-order perturbation theory MP2/6-311+G (d,p), and both the stable geometries were obtained, the barrier of the isomerization reaction, which corresponds to the configuration I turning into the configuration II, is 32.10 kJ·mol-1, which implies the isomerization reaction is very difficult to occur. The percentage of the configuration I with low energy is much more than that of the configuration II with high energy based on Boltzmann distribution law, which shows that the configuration I is stabler at room temperature. The vibration frequency of the monomer was calculated based on the stable structures at the same level in anharmonic force field, the potential energy distribution（PED） of each vibration frequency was calculated and the normal modes were analyzed and assigned, and the absorption peaks between 2 000~2 500 cm-1 can be explained using double frequency and combined frequency. It was found that the calculated IR spectrum of the monomer matched up with the experimental gaseous IR spectrum. As to the dimer, the M06 density functional was employed to simulate the nature for including the corrective term of weak interaction, the calculated IR spectrum of the dimer in anharmonic force field was familiar to the experimental IR spectrum of the solid-state, based on the theoretical computation, the weak peaks appearing on 2 000~3 000 cm-1 wavenumbers correspond to all kinds of overtone vibrations, the infrared transition between the vibrational ground state, of which the quantum number is 0, and the second vibrational excited state, of which the quantum number is 2, is too weak and can be ignored, and these overtone peaks are mainly from the sum of the fundamental frequencies, due to the dimers binding together with hydrogen bonds instead of chemical bonds, the rigidity of dimers is lower, and the anharmonicity of dimers increases, the intensity of the related overtone peaks also increases with the anharmonicity, these peaks in the dimer become very evident compared with those in the monomer, which agree with the experimental spectrum, however, because of a variety of dimers and polymers in the actual solid state, the intensity of the absorption peaks of the hydroxyl is reduced and the peak width of that is widened, in addition to the lack of the suitable parameters to calculate weak interaction, the universal force field and reasonable dispersion correcton factors in quantum chemistry makes the calculated spectra have certain error compared with the experiment ones, further more, the natural bond orbital (NBO) analysis was performed to reveal the origin of interaction, and it was found that the second order stabilization energy from the oxygen atom in the carboxyl group as the donor and the hydroxyl as the acceptor is 121.4 kJ·mol-1, the binding energy between the dimer is 65.27 kJ·mol-1, the amount of transferred charge from the donor orbital to the acceptor orbital is 0.067 electron. The result showed that the intermolecular interaction of 3-furoic acid mainly originated from the intermolecular hydrogen bond. The Gibbs free energy change ΔG of the dimer under different temperatures were computed, the dimer will become unstable at 500 K for the ΔG of the dimer being positive value, the hydrogen bond is destroyed, and all the monomers will get together with molecular interaction.