Does repeat synthesis in materials chemistry obey a power law?

Finding examples where experimental measurements have been repeated is a powerful strategy for assessing reproducibility of scientific data. Here, we collect quantitative data to assess how often synthesis of a newly reported material is repeated in the scientific literature. We present a simple power-law model for the frequency of repeat syntheses and assess the validity of this model using a specific class of materials, metal-organic frameworks (MOFs). Our data suggest that a power law describes the frequency of repeat synthesis of many MOFs but that a small number of "supermaterials" exist that have been replicated many times more than a power law would predict. Our results also hint that there are many repeat syntheses that have been performed but not reported in the literature, which suggests simple steps that could be taken to greatly increase the number of reports of replicate experiments in materials chemistry.

Origin of π-Facial Stereoselectivity in Thiophene 1-Oxide Cycloadditions.

We report a DFT computational study (M06-2X) of π-facial selectivity in the Diels-Alder reactions of thiophene 1-oxide. The preference for the syn cycloaddition arises because the ground state geometry of thiophene 1-oxide is predistorted into an envelope conformation that resembles the syn transition state geometry. The syn distortion occurs to minimize the effect of hyperconjugative antiaromaticity in the thiophene 1-oxide, arising from overlap of the σ*SO with the π-system. The syn selectivity follows through to the product structure that is stabilized by a π-σ*SO interaction, related to the 7-norbornenyl ion stability.

Computational investigation of double nitrogen doping on graphene.

Density functional theory (DFT) calculations were performed to study doping of two nitrogen atoms at different positions on a finite-sized graphene model of C82H24. We examined 21 structures of double nitrogen doped graphene to calculate their relative stabilities. The structure with two nitrogen atoms located apart is the most stable among the positional isomers considered in this study. For double nitrogen doping within a six-membered ring, the 1,4-position is more preferred than 1,3- or 1,2-positions for the finite-sized single layer graphene sheet. Our computational study supports the experimental observation of two nitrogen atoms at the 1,3- and 1,4-positions in a single six-membered ring of graphene. Furthermore, the structures with N-N bond are the least stable among two nitrogen doped graphene structures. The effects of nitrogen doping and the positions of two nitrogen atoms on the HOMO-LUMO energy gap of pristine graphene were analyzed.