Artefactual pyruvate and 2-oxobutyrate produced by trimethylsilylation of methylmalonic and ethylmalonic acids in the presence of oxygen
Trimethylsilylation of methylmalonic and ethylmalonic acids in the presence of headspace atmospheric oxygen is shown to produce the trimethylsilyl derivatives of pyruvic and 2-oxobutyric acids, along with 2-hydroxy-2-methylmalonic and 2-hydroxy-2-ethylmalonic acids, respectively. This may lead to overestimation of these keto acids, if they were not oximated in the original sample, and the mistaken reporting of the 2-hydroxymalonates.
Trimethylsilylation of malonate ester enols.
Malonic acid silylates readily to yield the expected bis-trimethylsilyl (TMS) ester; this ester reacts further in the silylating mixture to yield a tris-TMS derivative, apparently through enolization of one of the ester groups. Methylmalonic and hydroxymalonic acids behave similarly. The methyl and ethyl esters of malonic acid also silylate once with some facility. Mass spectra of these derivatives are presented
Stretching frequency versus bond distance correlation of OD(H)⋯Y (Y N, O, S, Se, Cl, Br, I) hydrogen bonds in solid hydrates
From a compilation of spectroscopic and structural data of solid hydrates 61 different compounds containing more than 250 OD(H)⋯Y groups have been selected, for which uncoupled OD stretching frequencies, hydrogen bond distances and assignments of sufficient reliability and accuracy are available. ν(OD) versus R(O⋯Y) and R(H⋯Y) diagrams and calculated correlation curves are presented for Y  N, O, S, Se, Cl, Br, I. Depending on the scatter of points and the number of data included in the plots the predictive value and the statistical significance varies from very high for O, S and Cl acceptors down to rather poor for Br and I acceptors. At equal bond distances the frequencies may differ by up to about 150 cm−1 depending on the specific chemical nature of the proton acceptors included in a plot, while the influence of different cation—water contacts is less significant and distinct. Anion effects play, therefore, a dominant role in producing large scatters, while action effects and experimental inaccuracies are of minor importance. Furthermore it is shown, that the relation between ν(OD) and ν(OH) frequencies is almost perfect and the frequency—distance correlations involving ν(OD) are also representative without serious restrictions for corresponding correlations involving ν(OH).