The Transition State for Carboxylic Acid Deprotonation on Cu(100)

Abstract

The kinetics of acid deprotonation on the Cu(100) surface have been studied using four different fluorinated carboxylic acids (CF2HCO2H, CF3CO2H, CF2HCF2CO2H, and CF3CF2CO2H). All four acids adsorb molecularly on Cu(100) at 90 K but deprotonate during heating to form carboxylates on the surface at temperatures below 300 K. Temperature-programmed reaction spectroscopy and X-ray photoemission spectroscopy were used to verify that the acids deprotonate on the Cu(100) surface. Work function measurements were used to study the deprotonation kinetics during heating and to estimate the activation energy barriers ( ) to deprotonation. The nature of the transition state to acid deprotonation on Cu(100) was probed by analysis of linear free energy relationships (LFER) or correlations of with the acid substituent constants, σF. The field reaction constant, ρF, or the slope of the LFER was found to be ρF = −52 ± 13 kJ/mol in the limit of zero coverage and ρF = −19 ± 2 kJ/mol at a coverage of 1/2 ML. These values of ρF can be compared to the value of ρF = −104 kJ/mol for acid deprotonation in the gas phase. This comparison suggests that the transition state for acid deprotonation on Cu(100) must be anionic with respect to the reactant (RCO2H(ad) ↔ [RCO2 δ-···Hδ+]‡ → ).

Asymmetry Induction by Cooperative Intermolecular Hydrogen Bonds in Surface‐Anchored Layers of Achiral Molecules

“…Consequently, it is assigned to carboxylate formation, which agrees well with the peak shifts reported in the literature. [47][48][49] The ratio of carboxyl to carboxylate, extracted from fitted curves, amounts to 2:1, which indicates that only one out of three tmla carboxylic functionalities becomes deprotonated in the process of adlayer formation at elevated temperature. Furthermore, a remarkable change in the peak shape is apparent in the O1 s spectrum of this phase (Figure 1 d).…”

Visualization of nucleation and growth of supramolecular networks on Cu(001) and Au(111)

“…The IV curve from the β-phase is shifted by approximately 0.3 V to lower voltages with respect to the curve from the α-phase. This corresponds to a reduction of the work function in the β-phase, as is expected for a deprotonated acid [106].…”

“…To clarify the picture we obtained here by studying mostly the ordering on the mesoscopic scale with LEEM, further research with other techniques is required. For example by imaging directly the intermolecular bonds with high resolution STM [125,126] or by unambiguously assigning a deprotonation reaction with spectroscopic methods [106].…”

“…The molecule is a typical building block used for the formation of supramolecular or metal-coordinated networks on metal surfaces [12,26,43,25,19,44,38,78]. On Cu(001) at or above room temperature, BDA adsorbs in a flat lying geometry with the carboxylic acid groups deprotonated [106,11,107]. At low BDA coverage, the molecules form a 2D dilute phase without long range order.…”

Disrupting Aryl-CH···O Interactions on Pt(111) Through the Coadsorption of Trifluoroacetic Acid and 2,2,2-Trifluoroacetophenone (TFAP): Inhibition of Competing Processes in Heterogeneous Asymmetric Catalysis

“…Second, the number of possible TFAP-TFA-TFAP geometries depends on whether or not the acid is molecularly intact. Given that TFA is deprotonated on Cu(100) below room temperature [21], it can be assumed that it is in large majority deprotonated on Pt(111) at room temperature. However, the formation of TFA dimers (Fig.…”