Bordwell's method of overlapping indicators was used to determine the pK(a) values of some of the most popular (thio)urea organocatalysts via UV spectrophotometric titrations. The incremental effect of CF(3) groups on acidic strength was also investigated. The pK(a)'s are in the range of 8.5-19.6. The results may lead to a better understanding of noncovalent organocatalysis and may aid in future catalyst development.

The hydrogen‐bonding strength of a variety of commonly employed thiourea catalysts was quantified by using a trialkylphosphine oxide as a 31P NMR probe. Simple diarylthioureas and more complex bifunctional amine‐ and hydroxy‐substituted thiourea derivatives were examined. Their catalytic activity was determined in a Diels–Alder reaction, and the obtained pseudo‐first‐order rate constants were correlated with the 31P NMR chemical shifts. A linear correlation between both variables was observed throughout the functionalized thioureas. The 31P NMR probe correlation fared better in comparison to a pKa correlation. Accordingly, the quantification presented herein by using a 31P NMR probe offers an elegant way to estimate the catalytic activity of thiourea catalysts in hydrogen‐bond‐activated reactions such as the Diels–Alder reaction.

Soil organic carbon (SOC) has primary importance in terms of soil physics, fertility and even of climate change control. An intensively cultivated Cambisol was studied in order to quantify SOC redistribution under subhumid climate. One hundred soil samples were taken from the representative points of the solum along the slopes from the depth of 20-300 cm with a mean 1.2 % SOC content. They were measured by the simultaneous application of diffuse reflectance (240-1900 nm) and traditional physico-chemical methods in order to compare the results. On the basis of the results hierarchical cluster analyses were performed. The spatial pattern of the groups created were similar, and even though the classifications were not the same, diffuse reflectance has proven to be a suitable method for soil/sediment classification even within a given arable field. Both organic and inorganic carbon distribution was found a proper tool for estimations of past soil erosion process. Results show SOC enrichment on two sedimentary spots with different geomorphological positions. Soil organic matter compound also differs between the two spots due to selective deposition of the delivered organic matter. The components of low molecular weight reach the bottom of the slope and there can leach into the profile, while the more polymerised organic matter compounds are delivered and deposited even before, on a higher segment of the slope in an aggregated form. This spatial difference appears below the uppermost tilled soil layer as well; referring the lower efficiency of conventional ploughing tillage in spatial soil homogenisation.