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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Dimeric molecular association of dimethyl sulfoxide in solutions of nonpolar liquids
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Dimeric molecular association of dimethyl sulfoxide in solutions of nonpolar liquids

机译：非极性液体溶液中二甲基亚砜的二聚分子缔合

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摘要

Although many vibrational spectroscopic studies using infrared (IR) absorption and Raman scattering (RS) techniques revealed that dimethyl sulfoxide (DMSO) forms intermolecular dimeric associations in the pure liquid state and in solutions, the results of a number of dielectric relaxation studies did not clearly show the presence of such dimers. Recently, we found the presence of dimeric DMSO associations in not only the pure liquid but also in solutions of nonpolar solvents, such as tetrachloromethane (CCl _4) and benzene (Bz), using dielectric relaxation (DR) techniques, which ranged from 50 MHz to 50 GHz at 25 °C. The dimeric DMSO associations cause a slow dielectric relaxation process with a relaxation time of ca. 23 ps for solutions in CCl _4 (ca. 17 ps in Bz) due to the dissociation into monomeric DMSO molecules, while the other fast relaxation is caused by monomeric DMSO molecules with a relaxation time of ca. 5.0 ps (ca. 5.5 ps in Bz) at 25 °C. A comparison of DR and vibrational spectroscopic data for DMSO solutions demonstrated that the concentration dependence of the relative magnitude of the slow and fast DR strength corresponds well to the two IR and RS bands assigned to the vibrational stretching modes of the sulfoxide groups (S=O) of the dimeric associations and the monomeric DMSO molecules, respectively. Moreover, the concentrations of the dimeric associations ([DIM]) and monomeric DMSO molecules ([MON]) were governed by a chemical equilibrium and an equilibrium constant (K _d = [DIM] ~2[MON] ~(-1)) that was markedly dependent on the concentration of DMSO and the solvent species (K _d = 2.5 ± 0.5 M ~(-1) and 0.7 ± 0.1 M ~(-1) in dilute CCl _4 and Bz solutions, respectively, and dramatically increased to 20-40 M -1 in pure DMSO at 25 °C).
机译：尽管许多使用红外（IR）吸收和拉曼散射（RS）技术的振动光谱研究表明二甲基亚砜（DMSO）在纯液态和溶液中形成分子间二聚体缔合，但许多介电弛豫研究的结果尚不清楚表明存在这种二聚体。最近，我们发现介电弛豫（DR）技术不仅在纯净液体中，而且在非极性溶剂（例如四氯甲烷（CCl _4）和苯（Bz））的溶液中也存在二聚DMSO缔合，其范围为50 MHz在25°C下达到50 GHz。二聚体DMSO缔合会导致缓慢的介电弛豫过程，弛豫时间约为。 CCl _4中溶液的解离速率为23 ps（Bz中约为17 ps），这是由于解离成单体DMSO分子引起的，而另一个快速弛豫是由单体DMSO分子引起的，弛豫时间约为3 ps。在25°C下为5.0 ps（在Bz中约为5.5 ps）。 DMSO解决方案的DR和振动光谱数据的比较表明，慢速和快速DR强度的相对大小的浓度依赖性与分配给亚砜基团的振动拉伸模式的两个IR和RS波段很好地对应（S = O ）分别是二聚体缔合和DMSO单体分子。此外，二聚体缔合（[DIM]）和单体DMSO分子（[MON]）的浓度受化学平衡和平衡常数控制（K d = [DIM]〜2 [MON]〜（-1））。这明显取决于DMSO的浓度和溶剂种类（分别在CCl _4和Bz稀溶液中的K _d = 2.5±0.5 M〜（-1）和0.7±0.1 M〜（-1），并显着增加至在25°C的纯DMSO中为20-40 M -1）。

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