Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic-weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic-weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope-abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope-abundance variations potentially are large enough to result in future expansion of their atomic-weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope variations in materials of natural ter- restrial origin are too small to have a significant effect on their standard atomic-weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio.

Poly(isosorbide carbonate) (PIC) was synthesized by melt polycondensation of dimethyl carbonate (DMC) and isosorbide using lithium acetylacetonate (LiAcac) as the catalyst. The reaction conditions were optimized to achieve PIC with relatively high number‐average molecular weight (Mn) of 28,800 g/mol and isosorbide conversion of 95.2%. A series of poly(aliphatic diol‐co‐isosorbide carbonate)s (PAICs) were also synthesized by melt polycondensation of DMC with isosorbide and equimolar amounts of aliphatic diols (1,4‐butanediol, 1,5‐pentanediol, 1,6‐hexanediol, and 1,4‐cyclohexane dimethanol) in the presence of LiAcac and the TiO2/SiO2‐based catalyst (TSP‐44). PAICs with Mn values ranging from 18,700 to 34,400 g/mol and polydispersities between 1.64 and 1.69 were obtained. The 13C NMR analysis revealed the random microstructure of PAICs. The differential scanning calorimetry results demonstrated that all the PAICs were amorphous with a unique Tg ranging from 46 to 88 °C. The dynamic analysis results showed that the incorporation of linear or cyclohexane structure changed the dynamic mechanical properties of PIC drastically. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Difluoroalkylated compounds play a remarkably important role in life and materials sciences because of the unique characteristics of the difluoromethylene (CF) group. In particular, precise introduction of a CF group at the benzylic position can dramatically improve the biological properties of the corresponding molecules. As a consequence, difluoroalkylation of aromatic compounds has become a powerful strategy in modulating the bioactivities of organic molecules. However, efficient strategies to selectively synthesize difluoroalkylated arenes had been very limited before 2012. Traditional synthetic methods in this regard suffer from either harsh reaction conditions or narrow substrate scope, significantly restricting their widespread applications, particularly for late-stage difluoroalkylation of bioactive molecules. To overcome these limitations, a straightforward route to access these valuable difluoroalkylated skeletons is the direct introduction of the difluoroalkylated group (CFR) onto aromatic rings through transition-metal-catalyzed cross-coupling. However, because of the instability of some difluoroalkylated metal species, which are prone to protonation, dimerization, and/or generation of other unknown byproducts, it is difficult to selectively control the catalytic cycle to suppress these side reactions. In this context, we proposed the use of low-cost and widely available difluoroalkyl halides as fluoroalkyl sources for transition-metal-catalyzed difluoroalkylation reactions via cross-coupling. In this Account, we summarize our major efforts on copper-, palladium-, and nickel-catalyzed difluoroalkylations of aromatics with low-cost and widely available difluoroalkyl halides as fluoroalkyl sources. Four modes of catalytic difluoroalkylation reactions, including nucleophilic difluoroalkylation, electrophilic difluoroalkylation, radical difluoroalkylation, and metal-difluorocarbene coupling (MeDiC), have been demonstrated through careful modulation of the catalytic systems. Among these reactions, the MeDiC reaction represents a new mode of fluoroalkylation. These processes enable difluoroalkylation of a variety of aryl halides and arylboron reagents under mild reaction conditions. A wide range of difluoroalkyl halides, including activated difluoroalkyl halides (Cl/BrCFR, R = π system), unactivated difluoroalkyl halides (BrCFR, R = alkyl, H), and especially the inert and inexpensive industrial chemical chlorodifluoromethane (ClCFH), are applicable to these reactions, providing straightforward and facile routes to a diverse range of difluoroalkylated (hetero)arenes. These difluoroalkyl halide-based strategies can also be applied to prepare difluoroalkylated alkenes, alkynes, and alkanes and feature impressive advantages over conventional methods for the synthesis of difluoroalkylated compounds in terms of synthetic efficiency, functional group tolerance, and structural diversity. In particular, the late-stage difluoroalkylation of bioactive molecules through these processes offers good opportunities for the...