An extremely highly electrophilic heteroaromatic structure: 4,6-dinitrotetrazolo[1,5-a]pyridineElectronic supplementary information (ESI) available: Fig. S1 Effect of pH on the ionization of the OH group of C-4a to give the diadduct D-4a in aqueous solution. See http://www.rsc.org/suppdata/ob/b3/b306437a/

Abstract

A detailed thermodynamic and kinetic investigation of the reactions of 4,6-dinitrotetrazolo[1 ,5-a]pyridine (DNTP) with water and methanol has been made in the corresponding solvents. In aqueous solution, covalent addition of water to DNTP occurs with the exclusive formation of an anionic hydroxy sigma-complex C-4a which is half-formed in a 0.4 M HCl solution (pKa(sigma) = 0.4). This corresponds to a 3 pK-units jump in thermodynamic stability from the most stable hydroxy sigma-complex known so far, i.e. the hydroxy adduct C-3a of 4,6-dinitrobenzofuroxan (DNBF). DNTP forms similarly a very stable methoxy sigma-complex C-4b in methanol (pKa(sigma) = 2.64). Interestingly, the addition of methanol to DNTP also results in the partial formation of a neutral carbinolamine-type adduct (C-5b) at low pH. Rate and equilibrium constants pertaining to most of the reaction pathways involved in the interactions have been determined. In particular, the following rate constants k1(H2O) and k1(MeOH) for formation of C-4a and C-4b have been measured: k1(H2O) = 1.93 s(-1); k1(MeOH) = 3.50 s(-1), to be compared with k1(H20) = 0.035 s(-1); k1(MeOH) = 0.030 s(-1) for sigma-complexation of DNBF under similar experimental conditions. Altogether, the results obtained reveal that DNTP is a considerably more powerful electrophile than DNBF, the common reference as to whether an electron-deficient aromatic or heteroaromatic substrate may be accorded superelectrophilic properties in addition or substitution processes.

Electrophilicities of 4‐Nitrobenzochalcogenadiazoles

“…Another interesting result is the finding that nitrobenzoselenadiazole 1 b is 2 orders of magnitude more electrophilic than 1,3,5‐trinitrobenzene 8 ( E =‐13.19), the common reference aromatic electrophile in σ‐complexation processes …”

“…In an effort to obtain a quantitative measure of the reactivity of nitro derivatives of 2,1,3‐benzothiadiazole and 2,1,3‐benzoselenadiazole towards nucleophilic addition processes, we now report on the kinetic and structural analysis of the coupling reaction of 4‐nitrobenzothiadiazole 1 a and 4‐nitrobenzoselenadiazole 1 b with the reference nitroalkyl anions 2 a‐c (Scheme , Table ) in order to evaluate the electrophilic parameter E at the C‐7 position of the two electrophiles 1 a and 1 b according to Eq. (1) and to include them into the comprehensive electrophilicity scale of Mayr…”

The Ambident Reactivity of 2,4,6‐Tris(trifluoromethanesulfonyl)anisole in Methanol: Using the SO2CF3 Group as a Tool to Reach the Superelectrophilic Dimension in σ‐Complexation Processes

“…As discussed in depth in previous studies of the covalent addition of water or methanol to many electrophilic Meisenheimer structures, for example, DNBF, [3] as well as to various heterocyclic cations such as the isoquinolinium or tropylium cations 10 and 11, [3,13,15,35] the observed rate constant (k obsd ) is, at a given pH, the sum of the individual first-order rate constants for formation (k f ) and decomposition (k d ) of 8 d-Me [Eq. (10)].…”

“…[3, 5, [13][14][15] These studies have revealed that there is a close relationship between the thermodynamic reactivity of Meisenheimer electrophiles, as measured by the related pK [Eqs. (1) and (3)] to the formation of the corresponding adducts.…”

“…It thus appears that the water and methanol pathways contribute to some extent to the formation of all hydroxy and methoxy s complexes with pK H 2 O a 7-8 in water and pK MeOH a 9.5-10.5 in methanol, respectively. [13,15,16] It is these borderline pK a values that have commonly been the major criterion as to whether a neutral electron-deficient aromatic or heteroaromatic substrate may be accorded superelectrophilic properties. [13,16] Interestingly, we have recently shown that pK a values for s complexation in water and methanol are related through the relationship shown in Equation (5).…”