Acidities of radical cations derived from arylacetonitriles

Abstract

The equilibrium acidities of phenylacetonitrile, and 20 of its m-and p-substituted derivatives have been measured in Me2S0 solution. Their pK,'s plot linearly with those of the corresponding anilines.Combination of the pK,'s of these acids with their oxidation potentials, &,,(HA), and those of their conjugate bases, Ec,x(A-), provide an estimate of the acidities of the corresponding radical cations. The pKI,*+ values for ArCH2CN+', where Ar is Ph, 1-and 2-naphthy1, and 9-anthry1, are -32, -18.5, -17.5, and -1 I , respectively, compared to 21.9,2045.20.6.5, and 19.8 for the corresponding ArCHzCN acids. Acidities of PhCH(Me)CN+., PhZCHCN+', 9-CN-FlH+ . and Y- respectively, compared to 234, 17.5.8.3, and 13.6 for the corresponding acids from which they were derived. The homolytic bond dissociation energies (BDEs) for the benzylic C-H bonds in these arylacetonitriles, estimated by combining pK,lA with &&(A-), fall in the range of 69 kcalimol for 9-CN-XnH to 82 kcalimol for PhCHZCN. For GC,H4CH2CNt radical cations the acidities are decreased, relative to G = H, when G is an electron donor substituent and increased when G is an acceptor. The BDEs of the benzylic C-H bonds in GC6H4CH2CN are weakened by up to 4 k c a h o l by para donors and strengthened by up to 1.2 kcalimol by m-or p-acceptors. The significance of these changes in BDEs with regard to the use of 0' scales and the AAOP method for estimating substituent effects on radical stabilities is discussed.

Hartree–Fock and density functional theory study of remote substituent effects on heterolytic Fe―C bond energies of p‐G‐C6H4CH2Fe(CO)2(η5‐C5H5) and p‐G‐C6H4(H)(CN)CFe(CO)2(η5‐C5H5)

“…Thermodynamic studies of the important FpR complexes are notably scarce . In our laboratory, methods described by Venimadhavan et al , Bordwell et al , and Brauman for obtaining enthalpies of heterolysis (Δ H het ) for the cleavage of Fe―C bonds to produce resonance‐stabilized cations, anions were extended to the study of iron–carbon σ‐bond energies through the reactions of α‐cyanobenzyl anions [abbreviated as p ‐G‐PAN − , where PAN = C 6 H 4 CH(CN)] with Fp + BF 4 − formed in solution. However, the directly accurate experimental thermodynamic data were not available.…”

Cyanoalkylierung: Alkylnitrile in katalytischen C‐C‐Kupplungen

“…Gleichwohl steigert die Eingliederung einer geeigneten elektronenziehenden Gruppe in den aromatischen Ring, wie in Abbildung 2g e- zeigt, [5,11] die Azidität substituierter Benzylnitrile,w as die Erzeugung von a-Cyanocarbanionen durch milde Brønsted-Basen ermçglicht. Im Vergleich zu Alkylnitrilen weisen Benzylnitrile eine geringfügig hçhere Azidität auf (pK a 21.9 in DMSO), wenngleich diese immer noch unzureichend für eine katalytische Erzeugung dieser Spezies ist.…”

Development of Green/Red-Absorbing Chromophores Based on a Coumarin Scaffold That Are Useful as Caging Groups

“…No reaction occurred with phenylacetonitrile, whose acidity is much lower than that of 10 (pK a =12.3) 17 or malononitrile (pK a =11.1) 18 . Taking into account these results and the spectroscopic properties of 4 (see below), we selected the 4-nitrophenyl moiety for exploring the incorporation of different substituents at the ortho positions of the aromatic ring (CN,F and NO 2 ) with the aim of tuning the photophysical properties of the coumarin chromophore.…”

“…The reaction mixture was stirred at 160ºC under an Ar atmosphere for 15 h. Then, the solvent was removed under vacuum. The crude was dissolved in DCM and precipitated upon addition of cold hexane to give (E)-2-(2,4-dinitrophenyl)- (17). The published method with some modifications was followed to synthesize compound 17.…”