In present study the relevance of using the time-dependent density functional theory (DFT) within the adiabatic approximation for computing oscillator strengths (f) is assessed using different LDA, GGA, and hybrid exchange-correlation (XC) functionals. In particular, we focus on the lowest-energy valence excitations, dominating the UV/visible absorption spectra and originating from benzenelike HOMO(pi)-->LUMO(pi(*)) transitions, of several aromatic molecules: benzene, phenol, aniline, and fluorobenzene. The TDDFT values are compared to both experimental results obtained from gas phase measurements and to results determined using several ab initio schemes: random phase approximation (RPA), configuration interaction single (CIS), and a series of linear response coupled-cluster calculations, CCS, CC2, and CCSD. In particular, the effect of the amount of Hartree-Fock (HF) exchange in the functional is highlighted, whereas a basis set investigation demonstrates the need of including diffuse functions. So, the hybrid XC functionals--and particularly BHandHLYP--provide f values in good agreement with the highly correlated CCSD scheme while these can be strongly underestimated using pure DFT functionals. These results also display systematic behaviors: (i) larger f and squares of the transition dipole moments (mid R:mumid R:(2)) are associated with larger excitation energies (DeltaE); (ii) these relationships present generally a linear character with R>0.9 in least-squares fit procedures; (iii) larger amounts of HF exchange in the XC functional lead to larger f, R:mumid R:(2), as well as DeltaE values; (iv) these increases in f, mid R:mumid R:(2), and DeltaE are related to increased HOMO-LUMO character; and (v) these relationships are, however, not universal since the linear regression parameters (the slopes and the intercepts at the origin) depend on the system under investigation as well as on the nature of the excited state.

Pd(II)-Insertion into β-methylene C(sp3)–H bonds was enabled by a mutually-repulsive and electron-rich quinoline ligand. Ligand tuning has led to the development of a method that allows for installation of an aryl group on a range of acyclic and cyclic amides containing β-methylene C(sp3)–H bonds.

There have been numerous developments in C–H activation reactions in the past decade. Attracted by the ability to directly functionalize molecules at ostensibly unreactive C–H bonds, chemists have discovered reaction conditions that enable reaction of C(sp2)–H and C(sp3)–H bonds with a variety of coupling partners. Despite these advances, the development of suitable ligands that enable catalytic C(sp3)–H bond functionalization remains a significant challenge. Here, we report the discovery of a mono-N-protected amino acid (MPAA) ligand that enables Pd(II)-catalyzed coupling of γ-C(sp3)–H bonds in triflyl-protected amines (R–NHTf) with arylboron reagents. Remarkably, no background reaction was observed in the absence of ligand. A variety of amine substrates and arylboron reagents were cross-coupled using this method. Arylation of optically active amino acid-derived substrates also provides a potential route for preparing non-protenogenic amino acids.

In this article, as a first step to develop an efficient approximation for predicting the molecular electronic excited state properties at ab initio level, we propose local excitation approximation (LEA). In the LEA scheme, the only local electron excitations within selected substructure (Chromophore) are treated to calculate the targeted excited state wavefunctions, whereas the other electron excitations (local electron excitations in other substructure and charge-transfer excitations between different regions) are simply discarded. This concept is realized by using the localized molecular orbitals (LMO) localizing on the chromophore substructure. If the targeted transitions show the strong local character and the adequate substructure is selected as chromophore region, the LEA scheme can provide excited state properties without large loss of accuracy. The fatal slowdown of convergence speed of Davidson's iterative diagonalization due to the use of LMO can be avoided by additional transformation of LMOs. To assess the accuracy and efficiency of the LEA scheme, we performed test calculations using various compounds at configuration interaction single (CIS) and time-dependent Hartree-Fock (TDHF) level of theory.