Comparison of brönsted acidities of neutral NH-acids in gas phase, dimethyl sulfoxide and water

• Published in: International journal of mass spectrometry and ion processes Vol. 175; no. 1; pp. 61 - 69
• Main Authors: Koppel, Ilmar, Koppel, Juta, Maria, Pierre-Charles, Gal, Jean-Francois, Notario, Rafael, Vlasov, Vladislav M., Taft, Robert W.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.1998
• Subjects: Acidities in DMSO; FTICR; Gas-phase activities; NH-acids; Solvent effects; NH-acids; Gas-phase activities; FTICR; Acidities in DMSO; Solvent effects
• ISSN: 0168-1176; 1873-2801
• DOI: 10.1016/S0168-1176(98)00113-X

The Brönsted acidities of several neutral NH-acids (substituted diphenylamine, substituted anilines and imides) were measured in the gas phase (pulsed FT ICR spectrometry), dimethyl sulfoxide and aqueous solution. Comparison of the Brönsted acidities of neutral NH-acids in the gas phase, dimethyl sulfoxide and water was also carried out. It was shown that substituent effects on the acidity of the studied compounds are significantly attenuated by the transfer of the reaction series of acidic dissociation of neutral acids from the gas phase into dimethyl sulfoxide and water. The strongest solvent-induced attenuation of the substituent effects is characteristic of the meta-substituted anilines whose sensitivity towards substituent effects decreases with transfer from the gas phase into DMSO by 2.83 times and with transfer into water by 4.13 times. At the same time, the reaction series of para and/or ortho-π-acceptor substituted anilines, amides, imides and substituted diphenylamines are less sensitive to a change in gas phase for DMSO or water. In the special case of para-acceptor substituted anilines it was demonstrated that the specific solvation induced an increase in the acidity of the para- and/or ortho-acceptor substituted anilines as compared with the behavior of the corresponding meta-substituted anilines by amounts up to 10 pK a units.