The Role of Methyl Groups in the Formation of Hydrogen Bond in DMSO−Methanol Mixtures

Abstract

When examining the formation energetics of a hydrogen-bonded complex R-X-H...Y-R', focus has been almost always on the atoms directly involved, namely the atoms X, Y, and H. Little attention has been paid to the effects of the secondary alkyl groups R and R'. Taking dimethyl sulfoxide (DMSO)-methanol binary system as an example, we have studied the roles of the alkyl groups in stabilizing the hydrogen bonds by employing FTIR and NMR techniques and quantum chemical calculations. We found that methyl groups play different roles in response to the hydrogen-bonding interactions. The methyl groups of DMSO are electron-donating, whereas that of methanol is electron-withdrawing, both making positive contributions. The findings reveal non-negligible effects of secondary alkyl groups in hydrogen bonding interaction and may shed light on the understanding of other more complicated hydrogen-bonded systems in chemical and biological systems.

Comparative Study of Halogen‐ and Hydrogen‐Bond Interactions between Benzene Derivatives and Dimethyl Sulfoxide

“…Assignments of the 19 FNMR spectroscopy signals to the fluorine atoms in C 6 F 5 Br and C 6 F 5 Ia re displayed in Figure 5.…”

“…Single-point energy changes of the four complexes (C 6 F 5 HÀDMSO,C 6 F 5 ClÀDMSO,C 6 F 5 BrÀDMSO, and C 6 F 5 IÀDMSO) Figure 6. The molar fraction dependenceso fthe 19 FNMR spectroscopysignals in the C 6 F 5 BrÀDMSO(A) and C 6 F 5 IÀDMSO( B) systems. in their most stable forms as functions of the bond angle were calculated, and the results are shown in Figure 8w ith the corresponding angle shown in the inset.…”

“…[19,20] Briefly,a ne xcess IR spectrum is defined as the difference between the spectrum of areal solution and that of the respective ideal solution under identical conditions. The working equation for calculating the excess IR spectrum is given by Equation (1):…”

“…Although the methyl groups of DMSO do not participate directly in the formationo ft he halogen/hydrogen bonds, they donate electrons to the S=O group and contribute positively to the stabilityo ft he complexes.T his is in agreementw ith our earlier work on the back groups. [18][19][20] …”

“…1-Bromo-2,3,4,5,6-pentafluorobenzene (C 6 F 5 Br) and1 -iodo-2,3,4,5,6-pentafluorobenzene (C 6 F 5 I) weret he selected XB donors, DMSO was still taken as the XB acceptor. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) and 19 FNMR spectroscopy and ab initio calculations were employedt oi nvestigate the halogen-bonding properties. In particular,e xcessI Rs pectroscopy [18][19][20][21][22][23][24][25][26] was used to reveal details of the molecular interactions.…”