In this Perspective, we will focus on the use of both experimental and theoretical methods in the exploration of reaction mechanisms in homogeneous transition metal catalysis. We briefly introduce the use of Hammett studies and kinetic isotope effects (KIE). Both of these techniques can be complemented by computational chemistry - in particular in cases where interpretation of the experimental ...

Acid-catalyzed hydrocarbon reactions involve by far the largest amount of catalyst and the largest volume of transformation in oil refinery and chemical industry. However, despite the general agreement on the carbocationic nature of the reaction intermediates, the initial steps and the true nature of the cations on the surface are still open to debate. On these points our basic knowledge has ga...

Enantioselective copper(I) hydride (CuH)-catalyzed hydroamination has undergone significant development over the past several years. To gain a general understanding of the factors governing these reactions, kinetic and spectroscopic studies were performed on the CuH-catalyzed hydroamination of styrene. Reaction profile analysis, rate order assessment, and Hammett studies indicate that the turno...

The influence of electron donors and electron acceptors of variable strength in the 4 and 4' position of 2 and 2' propyl-bridged axial chiral biphenyl cyclophanes on their atropisomerization process was studied. Estimated free energies ΔG(‡)(T) of the rotation around the central biphenyl bond which were obtained from (1)H-NMR coalescence measurements were correlated to the Hammett parameters σ(...

Site-selective functionalizations of complex small molecules can generate targeted derivatives with exceptional step efficiency, but general strategies for maximizing selectivity in this context are rare. Here, we report that site-selectivity can be tuned by simply modifying the electronic nature of the reagents. A Hammett analysis is consistent with linking this phenomenon to the Hammond postu...

In analogy to 4-b-substituted benzoyl)-N-methylpyridinium cations (1 -X's), the title species (2-X's, -X = -0CH3, -CH3, -H, -Br, -COCH3, -N02) undergo two reversible, well-separated (E1122650 mV) one-electron reductions. The effect of substitution on the reduction potentials of 2-X's is much weaker than the effect of the same substituents on 1-X's: the Hammett p-values are 0.80 and 0.93 for the...

The effects of substituents on the pKas of a set of 16 substituted benzoic acids have been examined using density functional theory [B3LYP/6-311G(d, p)] calculations. A variety of quantum chemical parameters were examined as indicators for the variations observed in the experimental pKas, including the Löwdin, Mulliken, AIM, and natural population analysis charges (QL, QM, QA, and Qn) on atoms ...

The methane negative chemical ionization (NCI) mass spectra of the medically important 1,3-dihydro-5-phenyl-1,4-benzodiazepin-2-ones generally consisted solely of M- and (M-H)- ions. Attempts to find the location of the H lost in the generation of the (M-H)- ion were unsuccessful, although many possibilities were eliminated. A Hammett correlation analysis of the relative sensitivities of a seri...

A new class of highly fluorescent 9,9′-bis-(alkyl)-2,7-diarylfluorene having electron withdrawing or electron donating groups on the p-phenyl positions were synthesized and characterized. The highly luminescent fluorene derivatives, 1–6 showed blue emission (376–416 nm), narrow FWHM (~ 50 nm), high quantum yield (φF = 0⋅12–0⋅87) and short fluorescence lifetimes, τF = 0⋅23–1⋅14 ns. The HOMO leve...

A dual-transducer approach based on sol-gel optical sensors was recently reported to measure acid and salt concentrations, C(acid) and C(salt), in concentrated aqueous LiCl-HCl, CaCl2-HCl, and AlCl3-HCl solutions (C(acid) at 5-6 M; C(salt) < or = 2 M). The scope of this new approach has been studied in salt-containing HCl solutions with C(acid) at 2-9 M, and factors that influence sensor respon...