Semiconductor Surface-Induced 1,3-Hydrogen Shift:  The Role of Covalent vs Zwitterionic Character

Abstract

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to compare the reaction of 1,2-cyclohexanedione (1,2-CHD) with Si(001) and diamond(001) surface dimers under ultra-high-vacuum conditions. 1,2-CHD is known to undergo a keto-enol tautomerization, with the monoenol being the primary equilibrium species in the solid and gas phases. XPS and FTIR data demonstrate that 1,2-CHD reacts with diamond(001) through the OH group of the monoenol, resulting in only one O atom being bonded to the surface. In contrast, XPS and FTIR data suggest that both oxygen atoms in the 1,2-CHD molecule bond via Si-O-C linkages to the Si(001) surface dimer, and that the molecule undergoes an intramolecular 1,3-H shift. While the Si(001) and diamond(001) surfaces are both comprised of surface dimers, the diamond(001) dimer is symmetric, with little charge separation, whereas the Si(001) dimer is tilted and exhibits zwitterionic character. The different reaction products that are observed when clean Si(001) and diamond(001) surfaces are exposed to 1,2-CHD demonstrate the importance of charge separation in promoting a 1,3-H shift and provide new mechanistic insights that may be applicable to a variety of organic reactions.

Chemical manipulation of multifunctional hydrocarbons on silicon surfaces

“…A theoretical analysis by Barriocanal Fig. 3.25 [246]. The proposed product of this reaction is identical to the Diels-Alder adducts considered above; however by comparing the chemistry of 1,2-cyclohexanedione on Si(100-2×1 and C(100)-2×1, the authors could infer several important points about the role of the dimer structure in determining the surface reaction pathway, specifically the fact that the zwitterionic silicon dimer induces an intramolecular 1,3-hydrogen shift that was previously never reported on a surface.…”

“…In selected examples of silicon surface chemistry this energy requirement may contribute to the barriers of the reactions that need the s-cis diketone as a reactant. One of the recent examples of diketone chemistry that overcomes the issue of s-cis vs. strans α-diketone is the reaction of 1,2-cyclohexanedione with Si(100) and C(100) surface by Hamers group[245,246]. As opposed to the diamond surface, where the chemisorption occurs via a dissociation of an O-H group of the enol form, resulting in only one O atom bonded to the surface, bonding to the Si(100)-2×1 surface occurs via two Si-O-C linkages and an intramolecular 1,3-hydrogen shift is observed as illustrated by a mechanism proposed in…”

Reaction of acetonitrile with the silicon(001) surface: A combined XPS and FTIR study

“…8a [21]. A 1,3-H-transfer has previously been observed for 1,2-cyclohexanedione on Si(0 0 1), and was attributed to the ability of a Si@Si dimer to accept charge, and it might be possible for a H transfer to occur for acetonitrile as well [48]. The C@C@N configuration that would result from the mechanism shown in Fig.…”

One-Step Direct Fixation of Atmospheric CO2 by Si-H Surface in Solution

“…At first, there is only silicon powder and only two strong Si-O peaks at 1,050 and 1,090 cm À1 . After the addition of HF solution and exposure of the silicon to CO 2 atmosphere, these two Si-O peaks disappear gradually and various new peaks appear; the peaks at 1,145 and 1,218 cm À1 belong to C-F bonds (Wang et al, 2016;Li et al, 2016); those at 1,030, 1,042 and 1,084 cm À1 are attributed to Si-O-C bonds (Schwartz et al, 2006;Jung and Park, 2011); and peaks at 920, 975, and 1,200 cm À1 are assigned to C-H bonds. With the increase of time, the intensity of C-F vibration becomes stronger (Figure 3B), indicating increase in the F-POM product.…”