The gas-phase basicity of hydroxamic acid derivatives

Abstract

mation of the secondary alcohol 6c would be consistent with a transition state, as in 10, again resembling a structure leading to the more stable carbenium ion 12a. In this situation, however, the more stable carbenium ion site is the primary carbon, because the positive charge can be stabilized by carbon-silicon -bond hyperconjugation (12b).19Experimental Section General Procedures. All steps in the preparation, transfer, and main reactions of the organometallic reagents studied here were conducted under an atmosphere of anhydrous and oxygen-free argon. All solvents and apparatus were likewise freed of traces of dissolved or adsorbed moisture and oxygen and then maintained under argon. Methods and techniques for working under anhydrous and anaerobic conditions and for conducting standard chromatographic and spectrometric analyses have been described previously.20Starting Materials and Products. Diisobutylaluminum hydride and triisobutylaluminum were obtained as neat reagents from Texas Alkyls Inc., Deer Park, TX. Diisobutylaluminum sec-butoxide was generated in situ by the cautious treatment of i-Bu2AlH in heptane with 1 equiv of sec-butyl alcohol.1,2-Epoxydecane and styrene oxide were commercially available and (epoxyethyl)triphenylsilane was prepared from the epoxidation of triphenylvinylsilane with m-chloroperbenzoic acid.21The reaction products 1-decanol, 2-decanol, 1-phenyl-l-ethanol, and 2-phenyl-l-ethanol were purchased, while the l-(triphenylsilyl)-l-ethanol and 2-(triphenylsilyl)-l-ethanol were synthesized by known procedures.22 (19) Any electrophilic attack on 5c, such as where E = MeAlCl2, is known to favor formation of the carbenium ion ß to silicon jse.

Modeling of Protonation Processes in Acetohydroxamic Acid

“…for the formohydroxamic acid at the MP2(FC)/6-311++G(d,p)//HF/6-311G(d,p) level. The present result agrees with the conclusion of Decouzon et al, obtained by comparison of FT-ICR results for acetohydroxamic acids and alkyl-substituted amides, regarding preferred protonation on oxygen.…”

“…By similarity with the chemical behavior of amides, it is usually accepted that the protonation site is the carbonyl oxygen ,, rather than the nitrogen or the OH group. However, Fourier transform ion cyclotron resonance (FT-ICR) studies of gas-phase basicities on the acetohydroxamic acid and its N -methyl and O -methyl derivatives do not provide conclusive results. In this context, 14 N NMR measurements on acetohydroxamic acid in aqueous solution seem to support protonation on the oxygen …”

Gas-phase basicities of polyfunctional molecules. Part 4: Carbonyl groups as basic sites

“…Gas‐phase basicity of several aliphatic carboxamides has been determined by the equilibrium method in FT‐ICR mass spectrometers (Decouzon et al, ; Homan et al, ; Witt and Grützmacher, ,; Azeim & van der Rest, ). Carboxamides are significantly more basic than their keto homologues as shown by a comparison of the proton affinities of Schemes and .…”

“…10 kJ/mol than the tabulated value (PA exp ( 1 ) = 834.7 kJ/mol; Hunter & Lias, 1998, ). Gas‐phase basicity of methylated derivatives CH 3 CONHOH, 2 , CH 3 CON(CH 3 )OH, 3 , and CH 3 CONHOCH 3 , 4 were determined by the equilibrium method using FT‐ICR mass spectrometry (Decouzon et al, ). The authors concluded that protonation was also occurring at the carbonyl oxygen, PA values of these three molecules (854, 876, and 879 kJ/mol for 2 , 3 , and 4 , respectively) reflecting the polarizability effect of the methyl group.…”

Fourier transform-ion cyclotron resonance study of the gas-phase acidities of germane and methylgermane; Bond dissociation energy of germane

“…Negative ion-molecule reactions were monitored as previously described [22] by using the Fouriertransform-ion cyclotron resonance mass spectrometer constructed at the University of Nice-Sophia Antipolis, which has been described elsewhere [23]. Briefly, it consists of Bruker CMS 47 electronics, a Varian IS-in.…”