Controlling an S_N2 Reaction by Electronic and Vibrational Excitation: Tip‐Induced Ether Cleavage on Si(001)

Abstract

Controlling chemicalr eactions beyond thermally activated reaction schemes can open alternative reaction channels,a nd thus lead to new final products.H erein, we show for tetrahydrofuran (THF) cleavage on Si(001), the surface analogue of an S N 2reaction, that excitation by electrons from the tip of as canning tunneling microscope (STM) not only opens new reaction channels,b ut that different final products can be selectively addressed by the type of excitation: Above athreshold voltage of 2.5 V, direct excitation by electron transfer into the antibonding CÀOo rbital of the THF molecules induces ether cleavage of the datively bonded intermediate of THF on Si(001). Belowt he threshold, ether cleavage is induced by multiple excitation of vibrational modes. In both modes of excitation, additional final configurations were observed when compared to the thermally activated reaction. The branching ratios of the final configurations are different for the two different excitation mechanisms,which in turn can be controlled by the applied sample bias.

Ring-Opening Reaction of Tetrahydrofuran on Ge(100) Surface

“… 22 , 23 Recently, the ring-opening reaction of tetrahydrofuran on a Si(100) surface has been observed. 24 , 25 Similarly, C–O bond cleavage of diethyl ether on a Si(100) surface has also been reported, which is kinetically prohibited on Ge(100). 8 , 26 In addition to diethyl ether, it was briefly stated that the reaction of tetrahydrofuran on the Ge(100) surface occurs via dative bond formation but without any data being provided.…”

Сan Plasmon Change Reaction Path? An Unprecedented Regioselective Decomposition of Unsymmetrical Iodonium Salts

“…[27][28][29][30][31] As a result, three main hypotheses have been proposed: (1) reaction acceleration through plasmonic heating, (Figure 1A); [32][33][34] (2) transfer of a hot electron to the organic molecule, followed by the formation and relaxation of the excited state (Figure 1B); and (3) intramolecular excitation of an electron to the LUMO orbitals via the decay of the optically excited surface plasmon (SP) (Figure 1B). 28,35,36 The all proposed mechanisms have been probed by theoretical and experimental studies in a range of (organic) transformations, but the final point in these discussions have not been set. One possible key issue into understanding the mechanism of plasmon-induced organic reactions involves analyzing their regioselectivity, which may act as a reporter of the reaction path of the interaction of the plasmon with the organic molecule.…”

“…39 The regioselectivity has been studied poorly, with only a handful of contributions dedicated to these issues, such as the regioselective cleavage of the C-O bond in the SN2 reaction. 36 However, the regioselectivity study is able to provide a deeper insight into the mechanism issues from the chemistry point of view and predict new possible pathways for plasmon-induced transformations.…”