Phosphates D'énols: XI—Étude en Spectrométrie de Masse des Dérivés Diméthyliques

The mass spectrometric study of a series of enolic phosphates of type A leades to fragmentation patterns influenced by the nature of the substituents (R, R′ and R″). It is generally observed that a simple or double hydrogen rearrangement occurs with the loss of the enolic groups. When R and R′ are alkyl groups, the migrating groups are the hydrogen atoms on the alkyl group at position 1. When there is no alkyl group at position 1, the hydrogen atoms of the alkyl group at position 2 induce the rearrangement process. Finally, if R, R′ and R″ are hydrogen atoms, the loss of the enolic chain occurs without any rearrangement.     

The mass spectra of ω-amino acid derivatives. The role of ω-activation in production of ions upon electron-impact

The mass spectra of a series of N-phthaloyl and N-trifluoroacetyl derivatives of ω-amino acids ranging from 3-aminopropionic acid to 6-aminohexanoic acid were determined. Ions of significant intensity resulting from the loss of neutral fragments from precursor ions were observed. Deuterium labeling studies indicate the initial fragmentation loss of a neutral molecule; i.e. the loss of water from the molecular ion involves ω-hydrogen loss from the alkyl chain. A fragmentation scheme consistent with metastable, high resolution and deuterium labeling data is presented.     

Fragmentation de la Méthyl-2 Indolizine sous Impact Electronique: perte de H˙ à partir de l'Ion Moléculaire; perte de HCN à partir de l'Ion [M?H˙]+

The origin of the hydrogen radical lost in the ionization chamber from the molecular ion of 2-methylindolizine has been studdied by examination of the spectra of four specifically deuterated species. Hydrogen loss involves preferentially a hydrogen from the methyl substituent but also one of the hydrogens of either ring, especially those of the 5-membered ring. The HCN elimination from the metastable [M? H^˙]⁺ ions was studied using a linked scan method; the results are consistent with loss of identity of all the hydrogen atoms of the precursor ion, which implies an extensive reorganization prior to fragmentation.     

Structural characterization of the regioisomers of di(hydroxybutyl) ether by GC‐EI MS and theoretical calculations

Di(hydroxybutyl) ether (DHBE), a liver protecting drug, is composed of a mixture of three regioisomers: 4‐(3‐hydroxybutoxy)‐2‐butanol (1), 3‐(4‐hydroxy‐2‐butoxy)‐1‐butanol (2), and 3‐(3‐hydroxybutoxy)‐1‐butanol (3). Unequivocal differentiation of each regioisomer of DHBE was rapidly obtained without isolation of the single components, using GC‐MS with electron ionization (EI). The mass spectrum of 1 showed a rearrangement ion at m/z 118, characteristic of the 3‐hydroxybutyl chain, deriving from loss of acetaldehyde from the molecular ion, whereas 2 and 3 were characterized by the ion at m/z 117, expected from α‐cleavage of the 4‐hydroxy‐2‐butyl chain. The species at m/z 118, in turn, loses a water molecule via a mechanism involving both alcohol hydrogens, as shown by deuterium exchange experiments. Both this finding and theoretical calculations support a mechanism in which the loss of acetaldehyde in 1 occurs via a cyclic intermediate, stabilized by a strong hydrogen bond between the alcohol oxygen bearing the charge and the other alcohol oxygen, and involves initial hydrogen transfer from the former to the latter. The EI spectrum of 2, having two 4‐hydroxy‐2‐butyl chains, showed the fragmentations expected from classical fragmentation rules of aliphatic ethers and alcohols, whereas the EI spectrum of 3, bearing one 4‐hydroxy‐2‐butyl and one 3‐hydroxybutyl chain, showed essentially the characteristic fragments of both chains. Copyright © 2009 John Wiley & Sons, Ltd.     

Résonance magnétique nucléaire de 13C et 17O d'éthers aliphatiques. Effets γ entre les atomes d'oxygène et de carbone

The ¹³C- and ¹⁷O-chemical shifts of 31 aliphatic ethers are measured and discussed. The ¹⁷O-chemical shifts of the ethers ROR′ correlate with chemical shifts for the methylene groups of the corresponding alkanes RCH₂R′. The constant of proportionality can be related to the orbital expansion term 〈r^?3〉_2p. The δ_c for carbon atoms can also be correlated with δ_c for the corresponding alkanes. The origin of the correlation is discussed taking into account the conformational modifications resulting from introduction of an oxygen atom in an alkyl chain.     

Diphenylprolinol Silyl Ether Catalyzed Asymmetric Michael Reaction of Nitroalkanes and β,β‐Disubstituted α,β‐Unsaturated Aldehydes for the Construction of All‐Carbon Quaternary Stereogenic Centers

The asymmetric Michael reaction of nitroalkanes and β,β‐disubstituted α,β‐unsaturated aldehydes was catalyzed by diphenylprolinol silyl ether to afford 1,4‐addition products with an all‐carbon quaternary stereogenic center with excellent enantioselectivity. The reaction is general for β‐substituents such as β‐aryl and β‐alkyl groups, and both nitromethane and nitroethane can be employed. The addition of nitroethane is considered a synthetic equivalent of the asymmetric Michael reaction of ethyl and acetyl substituents by means of radical denitration and Nef reaction, respectively. The short asymmetric synthesis of (S)‐ethosuximide with a quaternary carbon center was accomplished by using the present asymmetric Michael reaction as the key step. The reaction mechanism that involves the E/Z isomerization of α,β‐unsaturated aldehydes, the retro‐Michael reaction, and the different reactivity between nitromethane and nitroethane is discussed.     

Metastable [C4H8O]+˙ ions: Additional decompositions via the [2-butanone]+˙ ion

The losses of methyl and ethyl through the intermediacy of the [2-butanone]⁺˙ ion are shown to be the dominant metastable decomposition of 14 of 19 [C₄H₈O]⁺˙ ions examined. The ions that decompose via the [2-butanone]⁺˙ structure include ionized aldehydes, unsaturated and cyclic alcohols and enolic ions. [Cyclic ether]⁺˙ [cyclopropylmethanol]⁺˙ and [2-methyl-1-propen-1-ol]⁺˙ ions do not decompose through ionized 2-butanone. The rearrangements of various [C₄H₈O]⁺˙ ions the the 2-butanone ion were investigated by means of deuterium labeling. Those pathways involve up to eight steps. Ions with the oxygen on the end carbon rearrange to a common structure or mixture of structures. Those ions which ultimately rearrange to the [2-butanone]⁺˙ ion then undergo oxygen shifts from the terminal to the second and third carbons at about equal rates. However, this oxygen shift does not precede the losses of water and ethylene. Losses of water and ethylene were unimportant for ions with the oxygen initially on the second carbon. Ionized n-butanal and cyclobutanol, but not other [C₄H₈O]⁺˙ ions, undergo reversible hydrogen exchange between the oxygen and the terminal carbon. Rearrangement of ionized n-butanal to the [cyclobutanol]⁺˙ ion is postulated.     

Spectres de masse des composés organiques. 4e communication. Fragmentation de l'hexane

With the help of metastable peaks and high resolution, and by making extensive use of deuterated species we determined the main paths of fragmentation of hexane. Beside the simple splitting of a C? C-bond there are a series of internal rearrangement reactions. The loss of neutral fragments from alkyl ions is often, but not always, statistical. A small primary (0.96) and an even smaller (0.99) secondary isotope effect for a hydrogen transfer can be observed.     

Préparation de polyesteramides alternés

The polycondensation of hydroxyamido acids of general formula HO-R₁-CO-NH-R₂-COOH provides alternating polyesteramides only when R₁ and R₂ are alkyl groups. These aliphatic alternating polyesteramides, according to their structural high regularity, possess a more important content of interchain hydrogen bonds than the random copolymers. The higher melting point of the random copolymers is attributed to the heterogeneity of amide group partition in the chain. The existence of a benzyl group in the structure of the hydroxyamido acids reduces the polycondensation ability and the molecular weights of the products are low. These aromatic monomers are thermally degraded, p-toluic acid evolving; ester and amide functions stoechiometric ratio is not maintained, but infrared and differential thermal analysis show that these aromatic polyestermides keep a reasonable structural regularity.     

Mécanismes de Fragmentation en Spectrométrie de Masse par Ionisation Chimique. IV—Fragmentation des Ions Oxiranes Protonés

Fragmentation of oxians after chemical ionization, leading to the loss of water, involves several steps. The opening of the ring is the determining step. The potential energy surface of this reaction is given for the 2-methyltetrahydrofuran.     

Mass spectra of 1-(2′-hydroxy-5′-alkylphenyl)-1-alkanone (E)-oximes

The mass spectra of 1-(2′-hydroxy-5′-alkylphenyl)-1-ethanone (E)-oximes 1–6 and 1-(2′-hydroxy-5′-methylphenyl)-1-alkanone (E)-oximes 7–12 are given and the major fragmentation pathways discussed. The simultaneous loss of water and alkyl moieties from the molecular ion indicates that a skeletal rearrangement take place and a cycloheptatrienyloheterocyclic system is formed. The McLafferty rearrangement, γ-fission in the side aliphatic chain and oxygen expulsion are discussed with evidence being drawn from accurate mass measurements, metastable ions and comparison with mass spectral data of related compounds.     

Uncatalyzed,Regioselective Oxidation of Saturated Hydrocarbons in an Ambient Corona Discharge

Atmospheric pressure chemical ionization (APCI) in air or in nitrogen with just traces of oxygen is shown to yield regioselective oxidation, dehydrogenation, and fragmentation of alkanes. Ozone is produced from ambient oxygen in situ and is responsible for the observed ion chemistry, which includes partial oxidation to ketones and C−C cleavage to give aldehydes. The mechanism of oxidation is explored and relationships between ionic species produced from individual alkanes are established. Unusually, dehydrogenation occurs by water loss. Competitive incorporation into the hydrocarbon chain of nitrogen versus oxygen as a mode of ionization is also demonstrated.     

Uncatalyzed,Regioselective Oxidation of Saturated Hydrocarbons in an Ambient Corona Discharge

Atmospheric pressure chemical ionization (APCI) in air or in nitrogen with just traces of oxygen is shown to yield regioselective oxidation, dehydrogenation, and fragmentation of alkanes. Ozone is produced from ambient oxygen in situ and is responsible for the observed ion chemistry, which includes partial oxidation to ketones and C?C cleavage to give aldehydes. The mechanism of oxidation is explored and relationships between ionic species produced from individual alkanes are established. Unusually, dehydrogenation occurs by water loss. Competitive incorporation into the hydrocarbon chain of nitrogen versus oxygen as a mode of ionization is also demonstrated.     

Fragmentation des aldehydes cyclopropaniques en spectrometrie de masse: Intervention d'interactions bifonctionnelles

The mass spectra of aliphatic aldehydes which contain a cyclopropane group included in the polymethylenic chain, in some instances, show two intense peaks, called A and B that are not encountered either in other cyclopropane-containing aliphatic compounds or in other aliphatic aldehydes. The intensity of peaks A and B is strictly dependent upon the distance between cyclopropane and aldehyde. When the number x of methylene groups between the two functions is equal to 4 or higher than 10, peaks A and B are intense, but when x is equal to 7, the peaks are small.Specific labelling shows that ion A contains the atoms of the cyclopropane ring, the polymethylenic chain between the two functions and the aldehyde function. Ion B also contains the aldehyde function and results from the expulsion of the polymethylenic interfunctional chain to which a hydrogen atom of the other part of the molecule is added. This hydrogen atom arises, to an extent of about 60%, from the methylene of the cyclopropane ring. A mechanism is proposed in which cyclization of the molecular ion occurs; ion A is obtained by direct α-cleavage to the ether function in the cyclic ion; ion B results from alternative ether-cleavage causing opening of the carbo-ring. One hydrogen from the cyclopropane ring is transferred leading to the elimination of the interfunctional chain.The fact that formulas of ions A and B correspond to [C_nH_2n-3O]⁺ and that their intensities are dependent of x make questionable any structural determination established only by mass spectral examination of cyclopropane aldehydes.     

IsoméRisation avant la perte d'eau des ions aldéhydes et cétones protonés en spectrométrie de masse

Isomerization of Protonated Aldehyde and Ketone Ions in the Mass-Spectrography Before the Loss of Water In mass spectrometry, protonated aldehyde and ketone ions isomerize before the loss of a molecule of water. In order to specify this process, the spectra of deuterium labelled protonated aldehydes and ketones have been compared to the spectra of the corresponding isomer ions.     

Etude de la réactivité de la fonction carbonyle avec le cétène en présence d'un alcoxyde de titane. 1ère communication. Nouvelle méthode de synthèse de β-hydroxyesters

A new synthesis of β-hydroxyesters involving a reaction between a carbonyl compound, ketene and an alkyl-orthotitanate is described. The following carbonyl compounds have been studied: aldehydes, ketones, α-diketones, α- or γ-ketoesters. A reaction mechanism is proposed.     

Spectrométrie de Masse d'Hétérocycles Azotés. X–Contribution à l'Etude du Comportement de ll'Ion Aniline et des Ions Aminopyridines avant Fragmentation par Perte de HCN

The study of the mass analysed ion kinetic energy spectra of deuterated derivatives of aniline, aminopyridines and 2-chloro-5-aminopyridine shows that prior to HCN loss, hydrogen scrambling does not occur for aminopyridines and is limited but noticeable for aniline. In the case of this last compound the extent of scrambling varies markedly for small variations in the energy of the ions studied, these variations being within the energy window corresponding to metastable ions. Furthermore, an examination of the mass analysed ion kinetic energy spectra of monodeuterated derivatives of aminopyridines leads to the rejection of the generally accepted mechanism for HCN loss from the molecular ions of these compounds.     

Physico-chemical aspects of polyethylene processing in an open mixer. Part 28: Formal kinetics of aldehyde and carboxylic acid formation in the advanced stages

The rate of acid formation at high temperature is constantly increasing but temperature independent. Two main mechanisms can account for this behavior in the advanced stages of polyethylene processing. The first mechanism is based on free radical induced oxidation of aldehyde pairs that are formed on acid-catalyzed decomposition of allylic hydroperoxides. The last will be formed essentially on mechanical stress-induced oxygen addition to trans-vinylene groups. Peroxidation of one of the aldehydes might yield an acyl-peroxy radical that is likely to abstract the labile hydrogen atom from the second aldehyde. The acyl radical formed in the reaction will abstract a hydroxyl group from the peracid formed in the same reaction. This yields an acid and an acyl-oxy radical that will give a primary alkyl radical on decarboxylation. The second mechanism involves oxidation of ketones and alcohols that accumulate in the oxidizing melt. Acid-catalyzed decomposition of the α-keto-hydroperoxides yields simultaneously an acid and an aldehyde. Formal kinetics based on each mechanism shows that they do not involve significant activation energy, as it is required by the experimental data. The dependency on the oxygen concentration deduced from the formal kinetics for the oxidation of aldehyde pairs is in agreement with the experiments.     

The γ‐form of n‐eicosanol

In the crystal of the title compound, C₂₀H₄₂O, the mol­ecules are packed in layers parallel to the (100) plane. The alkyl chains are parallel to the [30] direction and these molecular chains are hydrogen‐bonded into chains parallel to the c axis. All C—C bonds of the alkyl chain show an antiperiplanar (trans) conformation, with a slight deviation from the ideal value (180°) in the C—C bonds close to the hydrogen bonds. The length of the alkyl chain is 27.92 (2) Å and the tilt angle is 59.7 (2)°.