By combining large basis and complete basis set (CBS) extrapolations of the coupled-cluster equilibrium geometry results with rovibrational and relativistic corrections, we demonstrate that it is possible to achieve near-quantitative accuracy for the NMR shielding constants in three group 15 trifluorides - NF3, PF3 and AsF3. These systems provide a rich test set for the calculation of dynamic electron correlation effects on NMR shielding constants. Basis sets as large as aug-cc-pCV6Z were employed, together with coupled-cluster expansion up to CCSDT, at the CCSD(T)/aug-cc-pCVTZ optimised geometries. The results of this work serve to highlight the application of state-of-the-art theoretical techniques which can be employed to guide and supplement NMR experimentation. Combining chemical shifts (either from experiment or high-level calculations) has also enabled a revised reference 19F NMR shielding constant for gas phase CFCl3 to be determined.

The molecular species C3H4O represents a striking example of an astrochemical conundrum.

A new robust surface-walking algorithm for locating transition states is presented. By modifying the Trust-Region Image Surface Minimization method to walk to higher-order stationary points, where the Hessian has more than one negative eigenvalue, we have developed an approach that determines transition states from above, by walking downhill on the potential energy surface. We call this algorithm “ALTRUISM”Alpine Trust-region Image Surface Method. We test the performance of the approach by applying it to a range of systems with several different quantum-chemical methods. Our results demonstrate that ALTRUISM is a systematic, robust, and unbiased method for connecting a reactant and a product via a transition state. The algorithmic combination of walking uphill (to different higher-order stationary points) and downhill to saddle points enables us to explore qualitatively distinct reaction pathways and construct a network of elementary reactions on a given potential energy surface.

A computational study of a set of synthetically unknown beryllium-containing rings, anionic analogues of antiaromatic boroles, has been carried out to investigate their structure, stability, and potential reactivity. The results indicate that these compounds should be electronically viable (as assessed from HOMO-LUMO and singlet-triplet gaps) and therefore potential targets for synthesis. In strong contrast with boroles, these beryllium species are predicted to be not Lewis acidic but rather Lewis basic, with reactivity centered on the endocyclic Be-C bond.

AE-CCSD(T)/cc-pVDZ optimized geometry ( Å)Trans-acrolein E: −191.416459970692500 a.u.