Origins of relative acidity: First and second period hydrides

Abstract

The origins of the trends of relatively acidity across and between the first and second period hydrides (BH3, CH4, NH3, H2O, HF, AIH3, SiH4, PH3, H2S, and HCl) were investigated using molecular and subsystem quantum mechanics at the Hartree‐Fock (HF)/6–31 + + G **//HF/6–31 + + G ** level of theory. The total deprotonation energies, Δ Eacid, are interpreted in terms of three component processes: Δ E1; deprotonation without electronic and nuclear relaxation; Δ E2, electronic relaxation within the acid geometry; and Δ E3, nuclear relaxation. Δ E1 is given from the electrostatic potential at the acidic proton, Δ E3 + Δ E2 (= Δ E *) is given from the calculated energy of the conjugate anion at the acid geometry. The increased acidity across a given period is shown to be already mostly an inherent property of the acid. © 1996 by John Wiley & Sons, Inc.

On the Relative Acidities of Organic Compounds: Electronic and Geometric Relaxation Energies

“…This is in line with the reasoning of Siggel and Thomas . The same result was obtained for quite different systems by Speers et al, Laidig and Streitwieser, and Tupitsyn et al A closer look at the data in Table reveals that the initial state electrostatic potential at the site of the acidic proton, V (H), is distinctly different for the four classes of compounds. I.e., for the alcohols − V (H) is 624−625 kcal/mol, which is smaller than − V (H) for the alkanes but larger than − V (H) for the enols or the carboxylic acids.…”

“…Further, trends for the relaxation energies R 1 and R 2 and for the electrostatic potential V (H) are discussed. This kind of analysis has also been applied to other systems: Speers et al have investigated the deprotonation of dimethyl sulfide, dimethyl sulfoxide, and dimethyl sulfone, and Laidig and Streitwieser have studied trends in acidity over the first and second period hydrides . Recently, Tupitsyn et al reported on the investigation of CH acidity trends in monosubstituted methanes…”

A Potassium Diboryllithate: Synthesis, Bonding Properties, and the Deprotonation of Benzene

“…Anionic mononuclear hydrides of p‐block elements possessing lower electronegativity exhibit a higher basicity in general, as theoretical calculations indicate. Accordingly, boron‐centered anions may exhibit a higher basicity than carbon‐centered anions . We recently reported the first isolation of a lithium salt of a boryl anion and demonstrated that the THF‐solvated boryllithium is able to deprotonate toluene and dihydrogen .…”

Boryllithium: Isolation, Characterization, and Reactivity as a Boryl Anion

“…1B, top) to satisfy the octet rule rather than deprotonation to form a boryl anion. Furthermore, electronegativity considerations predict lower stability for a boryl anion than for the corresponding carbanion (Pauling_s electronegativity: C, 2.55; B, 2.04) (20). Thus, we selected the reduction of a diaminohaloborane (5) for our synthetic approach to boryllithium (Fig.…”