Why Does Pivalaldehyde (Trimethylacetaldehyde) Unexpectedly Seem More Basic Than 1‐Adamantanecarbaldehyde in the Gas Phase? FT‐ICR and High‐Level Ab Initio Studies

Quintanilla, Esther; Dávalos, Juan Z.; Abboud, José‐Luis M.; Alcamı́, Manuel; Cabildo, Pilar; Claramunt, Rosa M.; Elguero, José; Mó, Otília; Yáñez, Manuel

doi:10.1002/chem.200400781

Cited by 14 publications

(8 citation statements)

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“…It should be underlined at this stage that several of the proton affinity values presented in Scheme are deduced from a correlation with ionization energies (Benoit & Harrison, , Bouchoux, ). An interesting case is that of 2,2‐dimethyl propanal (pivalaldehyde, 1 ) for which we deduce, from this correlation, a PA value of 806 kJ/mol (Scheme ) while an experimental value, recently obtained from bracketing experiments in a FT‐ICR mass spectrometer, was PA = 832 ± 5 kJ/mol (Quintanilla et al, ). This surprisingly high PA value has been interpreted by a facile isomerization of protonated pivaladehyde, 1H + , to protonated methyl‐isopropyl ketone, 2H + , via a pinacolic type rearrangement involving a combination of 1,2‐methide and 1,2‐hydride shifts (Scheme ).…”

Section: Aldehydes and Ketonessupporting

confidence: 60%

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

Bouchoux

2014

Mass Spec Rev

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This article constitutes the fourth part of a general review of the gas-phase protonation thermochemistry of polyfunctional molecules (Part 1: Theory and methods, Mass Spectrom Rev 2007, 26:775-835, Part 2: Saturated basic sites, Mass Spectrom Rev 2012, 31:353-390, Part 3: Amino acids, Mass Spectrom Rev 2012, 31:391-435). This fourth part is devoted to carbonyl containing polyfunctional molecules. After a short reminder of the methods of determination of gas-phase basicity and the underlying physicochemical concepts, specific examples are examined under two major chapters. In the first one, aliphatic and unsaturated (conjugated and cyclic) ketones, diketones, ketoalcohols, and ketoethers are considered. A second chapter describes the protonation energetic of gaseous acids and derivatives including diacids, diesters, diamides, anhydrides, imides, ureas, carbamates, amino acid derivatives, and peptides. Experimental data were re-evaluated according to the presently adopted basicity scale. Structural and energetic information given by G3 and G4 quantum chemistry computations on typical systems are presented.

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Section: Aldehydes and Ketonessupporting

confidence: 60%

“…More insidiously such reactions may occur inside proton transfer complexes and thus perturb gas‐phase basicity determination. Several examples of such behavior were identified for ketones (Quintanilla et al, ), diketones (Akrour et al, ) and substituted aromatic ketones or acid derivatives.…”

Section: Introductionmentioning

confidence: 99%

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

Bouchoux

2014

Mass Spec Rev

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“…The mechanism proposed to explain the formation of [MHH 2 O] + implies a transfer of the methyl group from C13 to C17, as presented in the upper part of Scheme . Such a 1,2‐transfer of a methyl anion to an adjacent positively charged carbon atom has been previously reported 22. The second hydrogen atom of the eliminated water molecule could come either from the methyl group on C17, through a four‐center concerted mechanism leading to the ion (b) in Scheme , or from the C14 position after the migration of a hydrogen atom from C14 to C13 via a four‐center concerted mechanism, leading to the ion (a) in Scheme .…”

Section: Resultssupporting

confidence: 63%

Elucidation of the decomposition pathways of protonated and deprotonated estrone ions: application to the identification of photolysis products

Bourcier

Poisson

Souissi

et al. 2010

Rapid Comm Mass Spectrometry

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With the future aim of elucidating the unknown structures of estrogen degradation products, we characterized the dissociation pathways of protonated estrone (E1) under collisional activation in liquid chromatography/tandem mass spectrometry (LC/MS/MS) experiments employing a quadrupole time-of-flight mass spectrometer. Positive ion and negative ion modes give information on the protonated and deprotonated molecules and their product ions. The mass spectra of estrone methyl ether (CH(3)-E1) and estrone-d(4) (E1-d(4)) were compared with that of E1 in order (i) to elucidate the dissociation mechanisms of protonated and deprotonated molecules and (ii) to propose likely structures for each product ions. The positive ion acquisition mode yielded more fragmentation. The mass spectra of E1 were compared with those of estradiol (E2), estriol (E3) and 17-ethynylestradiol (EE2). This comparison allowed the identification of marker ions for each ring of the estrogenic structure. Accurate mass measurements have been carried out for all the identified ions. The resulting ions revealed to be useful for the characterization of structural modifications induced by photolysis on each ring of the estrone molecule. These results are very promising for the determination of new metabolites in the environment.

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“…The activation barrier, estimated at the G3B3 level, is 60 kJ mol −1 . As previously suggested,17, 18 one may reasonably guess that this energy is provided by the strong interactions (hydrogen bonds and ion–dipole) that, under normal experimental conditions, occur between the neutral and deprotonated bases. These interaction energies are typically15 between 70 and 125 kJ mol −1 .…”

Section: Resultsmentioning

confidence: 69%

Gas‐Phase Protonation and Deprotonation of Acrylonitrile Derivatives NCCHCHX (X=CH₃, NH₂, PH₂, SiH₃)

Luna

Mó

Yáñez

et al. 2006

Chemistry A European J

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A combined experimental and theoretical study on the gas-phase basicity and acidity of a series of cyanovinyl derivatives is presented. The gas-phase basicities and acidities of (N[triple chemical bond]C--CH==CH--X, X=CH(3), NH(2)) were obtained by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry techniques. The corresponding calculated values were obtained at the G3B3 level of theory. The effects of exchanging CH(3) for SiH(3), and NH(2) for PH(2), were analyzed at the same level of theory. For the neutral molecules, the Z isomer is always the dominant species under standard gas-phase conditions at 298 K. The loss of the proton from the substituent X was found systematically to be much more favorable than deprotonation of the HC==CH linking group. The corresponding isomeric E ion is much more stable than the Z ion, so that only the former should be found in the gas phase. The most significant structural changes upon deprotonation occur for the methyl and amino derivatives because, in both cases, deprotonation of X leads to a significant charge delocalization in the corresponding anion. Protonation takes place systematically at the cyano group, whereby the isomeric E ion is again more stable than the Z ion. Push-pull effects explain the preference of aminoacrylonitrile to be protonated at the cyano group, which also explains the high basicity of this derivative relative to other members of the analyzed series that present rather similar gas-phase basicities, GB approximately 780 kJ mol(-1), indicating that the different nature of the substituents has only a weak effect on the intrinsic basicity of the cyano group. The cyanovinyl derivatives have a significantly stronger gas-phase acidity than that of the corresponding vinyl compounds CH(2)==CH--X. This acidity-strengthening effect of the cyano group is attributed to the greater stabilization of the anion with respect to the corresponding neutral compound.

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Why Does Pivalaldehyde (Trimethylacetaldehyde) Unexpectedly Seem More Basic Than 1‐Adamantanecarbaldehyde in the Gas Phase? FT‐ICR and High‐Level Ab Initio Studies

Cited by 14 publications

References 36 publications

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

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

Elucidation of the decomposition pathways of protonated and deprotonated estrone ions: application to the identification of photolysis products

Gas‐Phase Protonation and Deprotonation of Acrylonitrile Derivatives NCCHCHX (X=CH₃, NH₂, PH₂, SiH₃)

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Why Does Pivalaldehyde (Trimethylacetaldehyde) Unexpectedly Seem More Basic Than 1‐Adamantanecarbaldehyde in the Gas Phase? FT‐ICR and High‐Level Ab Initio Studies

Cited by 14 publications

References 36 publications

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

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

Elucidation of the decomposition pathways of protonated and deprotonated estrone ions: application to the identification of photolysis products

Gas‐Phase Protonation and Deprotonation of Acrylonitrile Derivatives NCCHCHX (X=CH3, NH2, PH2, SiH3)

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Gas‐Phase Protonation and Deprotonation of Acrylonitrile Derivatives NCCHCHX (X=CH₃, NH₂, PH₂, SiH₃)