Hydrogen Rearrangement Research Articles

Syntheses and Mass Spectral Studies of (E)‐1‐Alkanesulfonylpropenes and (E)‐1‐Alkanesulfinylpropenes

Abstract(E)‐1‐Alkanesulfonylpropenes and (E)‐1‐Alkanesulfinylpropenes have been synthesized in good to excellent yields. Studies correlating molecular structure and fragmentation patterns upon electron impact have been carried out. Double hydrogen rearrangements with the elimination of alkenyl radicals are the most facile fragmentations for (E)‐1‐alkanesulfonylpropenes. Single hydrogen rearrangement with alkene elemination is however the most important fragmentation for (E)‐1‐alkanesulfinylpropenes. In this case the hydrogen atom only migrates to the sulfinyl oxygen. These differences in fragmentation patterns between the (E)‐styryl‐alkyl‐sulfones/sulfoxides and the (E)‐propenyl‐alkyl‐sulfones/sulfoxides are attributed to the fact that different ionization sites are involved.

Mass spectrometric study of camptothecin and related compounds

In this paper the mass spectral reactions of camptothecin and its analogs(1～10) were studied with results showing main features of fragmentations under electron impact as follows: 1. Most of the compounds showed abundant molecular ion peaks as dictated by the aromatic character of the ring system. 2. The fragmentation chain was initiated by RDA of the lactone ring E, giving rise to intense intermediate ion (M-CO_2) followed by stepwise loss of neutral species CH_2CO, CO, etc. and thus resulting in the formation of stable ions containing highly conjugated A-B-C-D ring skeleton. 3. Camptothecin exhibited characteristic ion series m/z 205+14n and 206+14n in mass range 200～300, while its analogs displayed the corresponding peaks with a definite value of mass shift, depending on the size of the substituent at ring A, e. g.1u for NH_2, NHCOR; 2u for OH, OR. 4. All position isomers of camptothecin analogs with the same substituent at ring A showed identical spectra irrespective of the location of substituent at 9-C,10-C or 11-C. However, pronounced proximity effect was observed in case of 12-substituted analogs, which in turn furnished additional peaks produced by hydrogen rearrangement to the peri-nitrogen atom and this allowed to differentiate these particular compounds from their isomeric counterparts. The fragmentation mechanisms so far established were substantiated by high resolution data and metastable measurement and are useful in further structural elucidation of unknown alkaloids of the same series.

Mass spectrometry in structural and stereochemical problems. 2617—The effect of stereochemistry on the course of the characteristic ring D fragmentation of steroid hydrocarbons

AbstractThe ring D cleavage of the sterol skeleton with loss of carbon atoms 15, 16 and 17 together with the side‐chain is one of the most characteristic and structurally useful mass spectral features of steroids. It has been tacitly assumed that the hydrogen rearrangements accompanying this process are not sensitive to stereochemical changes. Using deuterium labeling it has now been demonstrated that the stereochemistry at various positions of the nucleus, notably 8, 9 and 14, strongly affects this process. Possible rationalizations for this unexpected observation are presented.

Fragmentations of organic negative ions. Mercapto acids and esters. A reinvestigation

Thioglycollates and β-thiopropionates with SH and/or CO2H groups yield pronounced (M-H)- ions in their negative ion spectra, not molecular negative ions as we previously reported. Compounds containing R1-S-CH2- functionality (R1 = alkyl or aryl) undergo α cleavage to S to yield R1S- and -S-CH2-ions. Hydrogen rearrangements are rare but thioglycollates R1SCH2CO2H characteristically eliminate R1SH to yield CH2CO2-. Fragment negative ions generally do not contain enough excess energy to allow decomposition, so we have studied their collision induced dissociations. Simple cleavage reactions are usual: for example BuSCH2CO2- decomposes to yield both BuS- and BuSCH2-. Group migration to sulfur is also observed; for example, ions -SCH2CO2R2 (R2 = alkyl or aryl) eliminate carbon dioxide to produce R2SCH2- as the major product.

ChemInform Abstract: MASS SPECTROMETRY OF 2‐ALKYLTHIO‐2‐METHYLPROPANOIC ACIDS AND THEIR ESTERS AND AMIDES. STRUCTURAL AND STERIC EFFECTS ON THE MCLAFFERTY REARRANGEMENT

AbstractDie massenspektrometrische Fragmentierung der nach bekannten Methoden synthetisierten 2‐Alkylthiocarbonsäurederivate (I)‐(III) wird systematisch untersucht.

RELATION STRUCTURE-FRAGMENTATION SOUS IMPACT ELECTRONIQUE. II STEREOSPECIFICITE DES REARRANGEMENTS A UN ET DEUX HYDROGENES EN SERIE TRIOXA-2,4,7 PHOSPHA-3 BICYCLO (4,4,0) DECANE

Abstract The origin of the hydrogen atoms implicated in the single and double hydrogen rearrangements (leading to [C6H9O]+ and [C6H8O]+ ions, whose relative abondance is typical of the phosphorus configuration) was investigated by means of selective deuteriation of the β and γ carbon (relative to phosphorus) of the isomeric 2,4,7-trioxa-3-methyl-3-phospha-3-thionobicyclo (4,4,0) decanes 1a and 1b. For both isomers the β hydrogen atoms are involved predominantly in the single hydrogen rearrangement. In the case of the double hydrogen rearrangement the hydrogens H1 (β) and H10, H10'(γ) for the a isomer and H6(γ) and H10, H10'(γ) for the b isomer are preferentialy transferred. The proposed fragmentation mechanisms attempt to explain the effect of the P[dbnd]S bond orientation on the fragmentation stereospecificity. La recherche de l'origine des atomes d'hydrogene impliques dans les fragmentations avec rearrangement a un ou deux atomes d'hydrogene (conduisant aux ions [C6H9O]+ et [C6H8O]+ dont l'abondance rel...

Vibrational spectroscopy of hydrogenated evaporated amorphous silicon films

The infrared absorption spectra of amorphous silicon films prepared by evaporation in a hydrogen beam are measured between 400 and 4800 cm −1. The dependence of the spectra on the temperature of the substrate and on the annealing temperature is investigated. A rearrangement of hydrogen to SiH sites at intermediate annealing temperatures (≈ 600 K) is observed, which parallels to the steep decrease of the electric room temperature dark conductivity. Impurity vibrations are also studied and a comparison is made with gdaSi and magnetron-sputtered aSi films, where the SiH strecthing mode near 2000 cm −1 predominates.

Electron impact induced water elimination from hydroxyamides. 2—N‐acetyl‐ and N‐benzoyl‐4a‐hydroxydecahydroquinoline and N‐Methyl‐4a‐hydroxy‐2‐oxodecahydroquinoline

AbstractElectron impact induced water elimination from the metastable molecular ions of N‐acetyl‐ and N‐benzoyl‐4a‐hydroxydecahydroquinoline mainly follows a formal [1,2] elimination. The initiating and ratedetermining step in the reaction is the hydrogen rearrangement from C‐8a onto the carbonyl group. The transferred hydrogen is subsequently lost, together with the hydroxyl group. The almost complete absence of H2O loss from both diastereomers of N‐methyl‐4a‐hydroxy‐2‐oxodecahydroquinoline confirms that the reaction can only proceed when the carbonyl group is able to function as ‘hydrogen carrier’ by occupying positions in the vicinity of both a hydrogen and the hydroxyl function.

Lignin depolymerizes coal at 300 °C

Liquefaction of coal requires thermal rupture of its carbon–carbon bonds to form free-radical fragments. Before these radicals can recombine or polymerize they must be stabilized by hydrogen atoms usually supplied by a hydrogen-donating solvent or by gaseous hydrogen. The conditions required for such liquefaction reactions are usually temperatures ≳400 °C and hydrogen pressures of several hundred atmospheres1,2. Often catalysts can be used to accelerate the breaking of carbon–carbon bonds and the transfer of hydrogen. Ouchi et al.5 reported that p-toluenesulphonic acid catalysed the depolymerization of coal. Darlage and Bailey6 investigated various solvents and Friedel–Crafts catalysts and found that repolymerization of the coal radical fragments was a predominant reaction when coal liquefaction was conducted in non-phenolic solvents such as toluene, xylene or tetralin. Heating coals in phenol at 425 °C was reported7 to cause extensive depolymerization accompanied by rearrangement of hydrogen to form a hydrogen-rich soluble fraction and a hydrogen-poor insoluble fraction. We now report that bituminous coal can be depolymerized at 300 °C by using, instead of phenol, the abundant, renewable raw material lignin which is a major component of all vascular plants. When a mixture of coal and lignin is reacted in a solvent in the presence of an acid catalyst both the coal and the lignin depolymerize in relatively mild conditions to form a filterable liquid product. The presence of the lignin increases substantially the amount of the coal that can be so liquefied.

Rearrangements in chemical ionization mass spectra

AbstractRearrangements reported in the literature for positive ions formed by chemical ionization are briefly reviewed, with particular emphasis on illustrative examples of hydrogen and skeletal rearrangements.

Mechanism of the elimination of methyl radical from the [M - H 2O] +· ion of 1,4-butanediol derivatives

Upon electron ionization 1,4-butanediol gives a fragment ion, ion k , 1 which is formed by loss of water and methyl radical from the molecular-ion. As the mechanism of the loss of water, leading to ion i , the precursor of ion k , has been discussed previously (ref. 1) this paper deals with the mechanism of the formation of ion k from ion i . The hydrogen rearrangement(s) preceding the loss of the methyl group could be [1,3]- and/or [1,2] migrations. It is shown by investigating appropriate deuterium labelled derivatives of 1,4-butanediol, that a double [1,2] hydrogen rearrangement is mainly operating upon formation of ion k .

Transport mechanism and its relationship with heterogeneity in a-Si: H

Hydrogen evolution and dc electrical conductivity measurement have been carried out for a-Si: H prepared by d.c. and r.f. glow discharge decomposition of silane. We show that the kink in log σ vs 1/ T plot can be explained in terms of the film heterogeneity. Kinks can appear or disappear after successive annealing depending on the specimens, and the upward shift in kink temperature by annealing is observed for the specimens showing kinks. These results are interpreted to be due to the structural and compositional change in heterogeneity caused by the diffusion and rearrangement of hydrogen.

Electron impact induced hydrogen rearrangements in (Z)‐ and (E)‐styryl alkyl sulfoxides

AbstractAlkene elimination, alkyl loss, styryl and alkyl migrations to oxygen are the major fragmentations of (Z)‐ and (E)‐alkane‐sulfinyl‐2‐phenylethenes (cis‐ and trans‐styryl alkyl sulfoxides) under electron impact. Alkene elimination has been found to go through a McLafferty‐type hydrogen rearrangement to yield the benzylic carbon and the sulfinyl oxygen, respectively. This is the most facile and interesting process for compounds with longer alkyl chains (R⩾C3H7), and is a unique feature for styryl sulfoxides. Product ion analyses show the migrating aptitude to carbon and to oxygen to be qualitatively similar.

An MO theoretical study on approximate potential energies of proton migration and fragmentation in protonated n-propanolamine and n-butanolamine.

Potential energies of proton migration and the H2, H2O, and NH3 elimination reactions in the protonated n-propanolamine were determined by MINDO/3. The elimination reactions in the protonated n-butanolamine were also examined and discussed in an attempt to explain the difference of the ratio of loss of water to loss of ammonia between these alcoholamines. Proton migration between carbon atoms in the protonated alkyl group was found to involve a low activation energy less than 84 kJ/mol but unlikely to take place because of other channels. Elimination of H2 was shown to take place from the C-protonated MH+ ion. There were several reaction paths for water and ammonia losses from the MH+ ion and the paths with hydrogen rearrangements were more likely to occur than the simple cyclization mechanism with the neighboring assistance of the hetero atom of the other end.

Mass spectrometry of 2-alkylthio-2-methylpropanoic acids and their esters and amides. Structural and steric effects on the McLafferty rearrangement.

The electron ionization mass spectra (MS) of S-methylated derivatives of N-(2-mercapto-2-methylpropanoyl)-L-cysteine and 2-alkylthio-2-methylpropanoic acids, as well as their esters and amides, were examined. Use of the deuterium labeling technique and accurate mass measurement supported the proposed fragmentation pathways. Extensive loss of CH2S from a molecular ion by the McLafferty rearrangement of a primary hydrogen is important in the MS of S-methyl compounds of amide derivatives. It was demonstrated that the intensity of the rearrangement ion decreases in the order of amide, ester, and acid, and in the case of amides the rearrangement is suppressed by the nonbonded interaction between methyl groups on the α carbon and the amide nitrogen.

Hydrogen rearrangements in ionized alkanoic acids. An ion lifetime study

Single and double hydrogen rearrangements involving β-bond cleavage have been studied in ionized butanoic, pentanoic and hexanoic acids specifically deuterium labelled at the hydroxy group and all carbon atoms of the side chains. The reactions have been studied in the range 6×10 −11-10 −5 s after ionization using the field ionization kinetic technique. At short ion lifetimes ( r<10 −10s) n-butanoic acid shows exclusively a single hydrogen rearrangement which specifically involves the γ-hydrogen and which is followed by β-bond cleavage. At longer ion lifetimes ( t>10 −8s) this rearrangement is preceded by hydrogen exchange between the hydroxylic hydrogen and the β- and γ-hydrogens as found previously. In ionized n-pentanoic and n-hexanoic acids, double hydrogen transfer with β-bond cleavage competes effectively with single hydrogen transfer at long ion lifetimes. At short ion lifetimes (< 10 −10s) single hydrogen rearrangement in n-pentanoic and n-hexanoic again involves predominantly the γ-hydrogen atom, the double hydrogen transfer involving those atoms from the γ- and δ-positions. In the acids extensive hydrogen exchange which is observed even on the picosecond time scale leads to participation of the β- and ϵ- (for n-hexanoic acid) positions in the hydrogen transfer reactions, although γ- and δ-hydrogens are predominantly involved even at the longest time (∼ 10 −5 s).

MNDO study of reaction paths: Hydroboration of carbonyl systems

The hydroboration reactions of acetaldehyde and acetone have been investigated by the MNDO method. The reactions have been shown to be twostep reactions involving an intermediate adduct. This adduct subsequently undergoes hydrogen rearrangement. The hydroboration reactions of acetaldehyde and acetone have been compared with the corresponding reaction of formaldehyde. The charge transfer effects accompanying these reactions have also been discussed.

ChemInform Abstract: A HYDROGEN REARRANGEMENT OF FORMAMIDINE AND THE SOLVENT EFFECTS THEREUPON

Chemischer InformationsdienstVolume 13, Issue 12 Preparative Organic Chemistry ChemInform Abstract: A HYDROGEN REARRANGEMENT OF FORMAMIDINE AND THE SOLVENT EFFECTS THEREUPON K. YAMASHITA, K. YAMASHITASearch for more papers by this authorM. KAMINOYAMA, M. KAMINOYAMASearch for more papers by this authorT. YAMABE, T. YAMABESearch for more papers by this authorK. FUKUI, K. FUKUISearch for more papers by this author K. YAMASHITA, K. YAMASHITASearch for more papers by this authorM. KAMINOYAMA, M. KAMINOYAMASearch for more papers by this authorT. YAMABE, T. YAMABESearch for more papers by this authorK. FUKUI, K. FUKUISearch for more papers by this author First published: March 23, 1982 https://doi.org/10.1002/chin.198212134AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue12March 23, 1982 RelatedInformation

HIGH-TEMPERATURE EVACUATED HYDROXYAPATITE AS A BASE CATALYST FOR THE ISOMERIZATION OF 1-BUTENE

Abstract Hydroxyapatite calcined in air did not show any catalytic activity for the isomerization of 1-butene even at 573 K, but hydroxyapatite evacuated above 773 K catalyzed the isomerization at 273 K selectively to form cis-2-butene by an intramolecular hydrogen rearrangement.

ChemInform Abstract: RADICAL ELIMINATIONS FROM GASEOUS CATION RADICALS VIA MULTISTEP PATHWAYS ‐ THE CONCEPT OF “HIDDEN” HYDROGEN REARRANGEMENTS

Chemischer InformationsdienstVolume 13, Issue 3 Reviews ChemInform Abstract: RADICAL ELIMINATIONS FROM GASEOUS CATION RADICALS VIA MULTISTEP PATHWAYS - THE CONCEPT OF “HIDDEN” HYDROGEN REARRANGEMENTS H. SCHWARZ, H. SCHWARZSearch for more papers by this author H. SCHWARZ, H. SCHWARZSearch for more papers by this author First published: January 19, 1982 https://doi.org/10.1002/chin.198203349Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue3January 19, 1982 RelatedInformation