bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometry of 2‐substituted‐1‐keto‐3‐aryl‐5H‐imidazo‐(1,5‐a)‐pyrroles derived from Schiff bases of N‐terminal prolyl peptides
Authors: Hamilton R. E. , Patil G. V. , Jayasimhulu K. , Day R. A. 
Published: May 2005

AbstractWe have been able to extend the use of Schiff base derivatives in peptide sequencing to N‐terminal prolyl peptides. Earlier studies from this laboratory revealed that certain aromatic Schiff bases of peptide esters gave electron‐impact mass spectra with relatively intense molecular, sequence and internal fragment ions. We observed that the reaction of N‐terminal prolyl peptide esters with 4‐dimethylaminonaphthaldehyde, p‐dimethylaminobenzaldehyde and 2‐pyridinecarboxaldehyde gave cyclization products which were found to be 2‐substituted‐1‐keto‐3‐aryl‐5H‐imidazo‐[1,5‐a]‐pyrrole derivatives. The molecular ion and many of the expected cleavages were prominent in the mass spectra. Deuterium labeling at the α‐carbon, amide nitrogen, or other exchangeable positions has been used in assigning the structure. It was also confirmed by the fragmentation pattern of the products derived by permethylation of the peptide derivative with tetramethylammonium hydroxide. Comparable cleavage patterns were seen among the N‐terminal prolyl peptides examined. Proline amide gave the corresponding cyclized product. With the inclusion of N‐terminal prolyl peptides in the list of peptides that we have examined, we may now prepare volatile derivatives of peptides containing any of the protein amino acids in two steps: esterification and treatment with the appropriate aromatic aldehyde.
Mass spectra of B, B′‐disubstituted bis(amino)diboranes(4)
Authors: Hancock Kenneth G. , Uriarte Anthony K. 
Published: May 2005

AbstractThe mass spectra of five B,B′‐disubstituted derivatives of the bis(amino)diboranes(4). Most of the fragmentations postulated have a precedent in similar processes of isoelectronic and/or isopolar species and are supported by the occurrence of metastable peaks.
Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen. IX—Struktur der Stabilen [C9H11]+‐Ionen aus Isomeren C9H11‐Chloriden
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand 
Published: May 2005

AbstractDie Struktur der stabilen [C9H11]+‐Ionen aus verschiedenen Modellverbindungen der Summenformel C9H11Cl wird mit Hilfe energetischer Messungen untersucht. Es wird ferner gezeigt, daß Acetylenverbindungen im Bereich der Auftrittspotentiale zu aromatischen Ionen cyclisieren.
Mass spectrometry of onium compounds. XXI—Substituent effect on the evaporation of anilinium oxides
Authors: El‐Mouafi Hamdi M. R. , Hvistendahl Georg , Undheim Kjell 
Published: May 2005

AbstractThe ionisation potentials and characteristic fragmentations of a series of anilinium oxides and their isomeric ethers have been used to assign structures for the gaseous species from the zwitterions. Transmethylation and direct evaporation of the zwitterions are competing processes. A bulky substituent ortho to the oxygen or a strongly electron attracting group in the 2‐isomer will prevent or reduce the transmethylation. If the volatility is much reduced, however, the temperature increase for evaporation results in transmethylation. The 4‐isomer was transmethylated even with two tert‐butyl groups ortho to the oxygen. The appearance potentials for an isomeric pair showed the energy difference between the zwitterion and the ether in the gas phase to be 11.5 kcal/mol.
Chemical ionisation mass spectra of explosives
Authors: Gillis R. G. , Lacey M. J. , Shannon J. S. 
Published: May 2005

AbstractThe chemical ionisation mass spectra of a number of representative explosives have been obtained using hydrogen as reagent gas. Fragmentation modes of the protonated molecular ions tend to be simple although some rearrangements have been noted. Loss of a radical from an even electron parent ion has been observed. The use of ‘ghost spectra’ for confirmation of the molecular weight of the sample is stressed: these consist of ions of low abundance resulting from reactions between sample ions and sample molecules. Labelling studies were carried out using deuterium as reagent gas.
Massenspektren Alicyclischer Verbindungen. IV—Die Massenspektren der Thiacycloalkanone und der Thiacycloalkanon‐1,1‐Dioxide
Authors: Herzschuh Rainer , Remane Horst 
Published: May 2005

AbstractDie elektronenstoßinduzierte Fragmentierung einer Reihe von 1‐Thiacycloalkanonen und 1‐Thiacycloalkanon‐1.1‐dioxiden mit 5 bis 8 Ringgliedern wurde untersucht. Die Ergebnisse wurden mit denen des Fragmentierungsverlaufes in den Cycloalkanonen, in den Thiacycloalkanen und in den 1‐Thiacycloalkan‐1.1‐dioxiden verglichen. Es Zeigte sich, daß in den Thiacycloalkanonen der bevorzugte Ort der Ladungslokalisierung der Schwefel ist.
Common electron‐impact fragmentations of 2‐methoxy‐8,9‐dehydroadamantane and 2‐exo‐methoxyprotoadamantene
Authors: Murray Roger K. , Jelus Barbara L. , Babiak Kevin A. 
Published: May 2005

Abstract2‐Methoxy‐8,9‐dehydroadamantane and 2‐exo‐methoxyprotoadamantene undergo common electron‐impact fragmentations at 70, 20 and 14.3 eV.
Isomerisation of hydrocarbon ions:I—Isomeric octanes: Acollisional actiation study
Authors: Levsen K. 
Published: May 2005

AbstractThe molecular ions of isomeric octanes retain their structural identity, while their alkyl fragments [CnH2n+1]+ (n = 3 to 7) isomerise to common structures prior to decomposition. Structures for [C6H13]+ and [C7H15]+ ions are proposed.
Mass spectrum and heat of formation of isocyanic acid. Production of [hco]+ from discrete electronic state of molecular ion
Authors: Compernolle F. 
Published: May 2005

AbstractThe appearance potentials for the transition ([HNCO]+·→ [HCO]+ + N), determined for the reaction in the ion source and in the first field free region (15·84 and 15·52 eV) correspond, respectively, to the vertical and adiabatic third ionisation potential of HNCO, as determined by photoelectron spectroscopy. The formyl ion and nitrogen radical are formed in the ground state, which requires predissociation of a quartet molecular ion of HNCO.A heat of formation δHf(HNCO)g = −25 ± 3 kcal mol·1 was determined from the appearance potential and kinetic energy release for the metastable ion [HCO]+, and from the difference in appearance potentials for the ion [NH]+· produced from the isoelectronic molecules HNCO and HN3.
Fragmentation sous impact electronique de l'acetate de tertiobutyle
Authors: Corval Madeleine 
Published: May 2005

AbstractL'examen des spectres de masse à resolution moyenne de l'acétate de tertiobutyle et de trois variétés marquées asu deutérium permet de déterminer les modes defragmentation à 70 e V, confirmés pour la présence de transitions métastables. Oute le réarrangement de McLafferty deux types de réarrangement moins classiques des ions oxygénés sont observés, et quelques effets d'isotopie sont mis en évidence.
Massenspektrometrische Untersuchung ungesättigter Carbonylverbindungen: Radikal‐eliminierung durch α‐Spaltung oder Cyclisierung?
Authors: Schwarz Helmut , Richter Bernd , Bohlmann Ferdinand 
Published: May 2005

AbstractDie Mechanismen der Alkyleliminierung aus verschieden Carbonylverbindungen werden diskutiert. Sowohl das Fragmentierungsverhalten als auch die Isomerisierungstendenz der Molek%uUl‐Ionen werden stark durch die Anzahl der Doppelbindungen, die Natur der Ketofunktion und die Position des eliminierten Radicals beeinfluust.
Ionisation potentials in structure analysis of isomeric nitrones, oxaziranes, O‐ether oximes and acid amides
Authors: Thorstad Olav , Undheim Kjell , El‐Gendy Mahmoud A. F. 
Published: May 2005

AbstractComparative studies of the ionisation potentials and the mass spectra of some isomeric nitrones, oxaziranes, O‐ether oximes and acid amides gave no evidence for hermally‐induced isomerisation in the mass spectrometer. Characteristic differences in the electron‐impact‐induced fragmentation patterns are discussed.
Effects of bifunctional interactions in the chemical ionization mass spectrometry of carboxylic acids and methyl esters
Authors: Weinkam Robert J. , Gal Joseph 
Published: May 2005

AbstractThe methane chemical ionization mass spectra of dodecan‐1, 10‐dioic acid and the methyl ester show enhanced water and methanol elimination relative to monofunctional analogs. Elimination of acetic acid from 1,10‐diacetoxydecane, however, was reduced relative to 1‐acetoxydecane. This appears to be the result of bifunctional interactions. The steric requirement of this interaction is shown in an homologous series of dicarboxyl compounds. The change in interfunctional separation is shown to affect the proton and ammonium ion affinities in the ammonia chemical ionization spectra of the dicarboxyl compounds in a manner explained in terms of proton and ammonium ion complex formation. The observation is extended to various other functional groups.
Differentiation of isomeric cyclic diamides by electron impact mass spectra
Authors: Foti S. , Montaudo G. , Lüderwald I. , Przybylski M. , Ringsdorf H. 
Published: May 2005

AbstractThe behaviour under electron impact of two series of isomeric cyclopentane‐ and cyclohexane‐1, 2‐ and ‐1, 3‐dicarboxylic acid dipiperidides was studied. Diagnostic fragmentation pathways were found to differentiate the isomeric diamides. Additional evidence was obtained from the metastable transitions.
Field desorption mass spectrometry of quaternary ammonium salts: Cluster ion formation
Authors: Veith H. J. 
Published: May 2005

AbstractThe field desorption mass spectra of salts such as quaternary ammonium and carbenium salts with organic cations in addition to high cation intensities show signals for cluster ions composed of the salt cation + salt molecule, i.e. [C + nM]+, n = 1–5, thus allowing determination of the molecular weights of salts. In some cases cluster ions of the type [nM – 1]+ are detected. Conditions for the formation of cluster ions are discussed.
On the formation of the [M  OH]+ ion in m‐nitrobenzaldoxime. evidence for a cyclohexadiene‐type intermediate ion
Authors: Vijfhuizen Peter C. , Verboom Wim , Heerma Wigger 
Published: May 2005

AbstractIn m‐nitrobenzaldoxime a strongly enhanced loss of OH⋅ is observed as compared with the p‐nitro compound. Evidence is presented for a fragmentation mechanism involving the formation of a cyclohexadiene‐type intermediate ion formed by a rearrangement of the hydroxyl hydrogen to the phenyl ring.
Massenspektrometrische Untersuchungen zu Dyotropen Umlagerungen
Authors: Schwarz Helmut , Kliment Miroslav , Reetz Manfred T. , Holzmann Gerhard 
Published: May 2005

AbstractDie elektronenstoßinduzierte spaltung der Sauerstoff‐Kohlenstoff‐(bzw. silicium)‐Bindung wird durch eine gleichzeitige Wanderung der Silylfunktion zum Sauerstoff ermöglicht. Der mechanistische Verlauf entspricht teilweise dem von dyotropen Umlagerungen.
Mass spectrometric studies of 6‐chloro‐6H‐dibenz[c,e] [1,2]oxaphosphorine‐6‐sulphide and its derivatives
Authors: Bhatia M. S. , Pawanjit  
Published: May 2005

AbstractThe electron‐impact induced fragmentation of 6‐chloro‐6H‐dibenz[c,e] [1,2]oxaphosphorine‐6‐sulphide and its 6‐ethoxy and 6‐hydroxy derivatives has been studied and it has been found that formation of the dibenz[c,e] [1,2]oxaphosphorin system and elimination of HCP are common features. β‐Hydrogen rearrangement, in the case of the ethoxy derivative, is comparable to ethers with a POCH2CH3 linkage.
Effect of substituent group interaction in the fragmentation of some pyrrolidin‐3‐ones
Authors: Cum Giampietro , Sindona Giovanni , Uccella Nicola 
Published: May 2005

AbstractThe decomposition after electron impact of someN‐alkyl andN‐aryl pyrrolidin‐3‐ones has been examined and fragmentation mechanisms influenced by the substituents on the nitrogen have been observed. Accurate mass measurement, deuterium labelling, kinetic energy release measurements and metastable (DADI) ion abundances, permit the elucidation of the probable mechanism of formation of the most intense fragment ions. The available experimental evidence indicates the occurrence of rearrangement processes leading to important product ions in the mass spectra of theN‐aryl derivatives. This type of fragmentation has been interpreted as the result of the combined action of two groups on the nitrogen atom of the heterocyclic nucleus.
Computer‐aided interpretation of mass spectra. STIRS prediction of rings‐plus‐double‐bonds values
Authors: Dayringer Henry E. , McLafferty F. W. 
Published: May 2005

AbstractThe number of rings‐plus‐double‐bonds (R + DB) in an unknown molecule can be predicted from its mass spectrum using the ‘Self‐Training Interpretive and Retrieval System’.2 The average R + DB value of the 15 compounds selected by the overall match‐factor (highest MF11.0 values) predicts the R + DB value of the unknown within ±1 of the correct value for predictions between 0 and 4 in 87% of the cases, and within ±2 for predictions between 5 and 11 for 77% of the cases.
Mass spectra of some perfluoroalkyl and perfluoroalkylether substituted 1,2,4‐oxadiazoles
Authors: Paciorek Kazimiera J. L. , Nakahara James H. , Kratzer Reinhold H. , Rosser Robert W. 
Published: May 2005

AbstractElectron impact fragmentation patterns were obtained for 1,4‐bis[(5‐perfluoro‐n‐heptyl)‐1,2,4‐oxadiazolyl]‐benzene, its perfluoroalkylether substituted analogue, 3,5‐bis(perfluoroalkyl)‐, 3,5‐bis(perfluoroalkylether)‐ and 3‐perfluoroalkylether‐5‐perfluoroalkyl‐1,2,4‐oxadiazoles. In the compounds containing the phenylene group the molecular ion constituted the base peak; the main process was the breakdown of the oxadiazole ring with concurrent liberation of the perfluoroalkyl or perfluoroalkylether nitrile molecule; cleavage of the fluorinated chain α to the oxadiazole ring was found to take place to a considerable degree. In the perfluorinated 1,2,4‐oxadiazoles cleavage β to the oxadiazole ring occurred preferentially; fragmentation of the ring itself took place to a limited degree only. The 3‐perfluoroalkylether‐5‐perfluoroalkyl‐1,2,4‐oxadiazole appeared to undergo the primary β‐cleavage exclusively at the perfluoroalkylether sidechain.
Hydrogen migrations in mass spectrometry. III–Energetics of formation of [R′CO2H2]+ in the mass spectra of R′CO2R
Authors: Benoit F. M. , Harrison A. G. , Lossing F. P. 
Published: May 2005

AbstractThe appearance potentials for the [R'CO2H2]+ ion produced in the fragmentation process \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm R}^{\rm '} {\rm CO}_{\rm 2} {\rm R}} \right]_{}^{_.^ + } $\end{document} → [R'CO2H2]++[R2H] have been measured using mono‐energetic electron impact techniques for ethyl, n‐propyl, and i‐propyl formates and acetates. The results indicate that at the threshold the product ion has the protonated acid structure with the hydrogen on the carbonyl and not the hydroxyl group, and that the neutral product for the propyl esters is the allyl radical and not the cyclopropyl radical. For the propyl formates and acetates the appearance potential of the [R'CO2H2]+ ion is identical with the adiabatic ionization potential of the parent ester (measured by photoelectron spectroscopy) indicating that fragmentation occurs for ground state molecular ions. A two‐step mechanism is proposed to rationalize the results.
A study of deuterium exchange in adamantane carboxylic acids and alcohols under electron impact
Authors: Yurchenko A. G. , Dovgan N. L. , Chizhov O. S. , Karpenko N. F. , Ya. Podel'ko A. 
Published: May 2005

AbstractThe mass spectra of 1‐adamantyl substituted carboxylic acids and alcohols with and without deuterated hydroxyl groups were studied. Deuterium exchange between functional group and adamantane nucleus was observed and a possible explantation of the phenomenon is given.
Mass spectrometry of transition‐metal π‐complexes. III—a study of an iron‐coordinated tautomer of phenol
Authors: Calleja J. , Davis R. , Ojo I. A. O. 
Published: May 2005

AbstractA study of the fragmentation of the \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{\left({{\rm C}_{\rm 6} {\rm H}_{\rm 6} {\rm O}} \right){\rm Fe}} \right]_{}^{_.^ + } $\end{document} ion formed from two different precursors suggests that the ions adopt different structures over that part of the energy distribution giving rise to decomposition in the ion source.
Equivalency of the carbon atoms in the molecular ion of cyclopropabenzene
Authors: Wentrup‐Byrne E. , Gülaçar F. O. , Müller P. , Buchs A. 
Published: May 2005

AbstractThe carbon atoms of the molecular and [MH]+ ions of cyclopropabenzene which are formed upon electron impact at 70 and at 12 eV lose their positional identity completely before C2H2 is expelled.
Mass spectra of substituted Δ2‐1,2,4‐oxadiazolines—I
Authors: Srivastava R. M. 
Published: May 2005

AbstractThe electron impact fragmentation of four Δ2‐1,2,4‐oxadiazolines with substituents at positions 3 and 5 has been examined. The direct analysis of daughter ions and high resolution mass measurements provided valuable information regarding certain ions. The present study clearly demonstrates that the substitution of phenyl or a substituted phenyl group for alkyl at C‐3 and alkyl in place of a phenyl substituent at C‐5 in the oxadiazoline system alters the fragmentation modes considerably.
Der massenspektrometrische Verlust eines N‐Substituenten aus monoacylierten 1.3‐Diaminopropanen
Authors: Eckhardt Gert , Gessi Ennio 
Published: May 2005

AbstractN‐Acyl‐N′,N′‐dialkyl‐1.3‐diaminopropane spalten beim elektronenstoßinduzierten Zerfall einen N‐Substituenten aus den Molekülionen ab. Die Natur aller N‐Substituenten bestimmt, ob vorzugsweise die Acyl‐ oder eine Alkylgruppe eliminiert wird.
Transfert d'Hétéroatomes (Cl, Br, OH) lors de la Fragmentation d'Acétyléniques δ‐Fonctionnalisés
Authors: Arseniyadis S. , Gore J. , Roumestant M. L. 
Published: May 2005

AbstractLes spectres de masse de trois alcynes δ‐fonctionnalisés montrent qu'il y a migration de chlore, de brome et. d'hydroxyle vers l'insaturation. La similitude existant entre ces spectres et ceux des composés alléniques isomères suggère qu'il y a transformation acétylène→allène après l'impact électronique.
Zum massenspektrometrischen Verhalten von Diarylaminen
Authors: Riepe W. , Zander M. 
Published: May 2005

AbstractZur Deutung des Fragmentierungsverhaltens von Diarylaminen im Massenspektrometer ist die Annahme von Carbazol‐Ringschlüssen am plausibelsten. Dabei kann zunachst eine Cyclisierung unter Abspaltung eines Wasserstoffatoms angenommen werden, wonach es in einem zweiten Schritt unter Abspaltung eines weiteren Wasserstoffs zur Ausbildung der Carbazolstruktur kommt. Wie durch die Untersuchung von 10 Diarylaminen gezeigt wird, hangt die Bereitschaft zum postulierten Ringschluß von der Größe des π‐Elektronensystems ab.
On the chemical ionization reactions of alkyl substituted cyclopropanes
Authors: Andrist A. Harry , Gemperline Paul J. , Chen Hsiao‐Chiung 
Published: May 2005

AbstractAs predicted by semi‐empirical molecular orbital calculations, the methane chemical ionization mass spectra of alkylcyclopropanes exhibit both proton addition and hydride abstraction processes; both the calculations and the observed substituent effects suggest the common intermediacy of gas phase cyclopropylcarbinyl cations. In agreement with this hypothesis are the results of an isotopic labeling experiment which identifies the reactive site as the cyclopropylcarbinyl carbon.
Mass spectral skeletal and hydrogen rearrangements in some bicyclic ketones
Authors: Henion J. D. , Kingston D. G. I. 
Published: May 2005

AbstractThe mass spectra of bicyclic ketones bicyclo[4.2.1]nonan‐9‐one, bicyclo[5.2.1]decan‐10‐one, bicyclo[4.3.1]decan‐10‐one and bicyclo[5.3.1]undecan‐11‐one specifically deuterated in positions both adjacent and nonadjacent to the carbonyl carbon have been investigated. The fragmentation and rearrangement processes predominating appear to be dictated by the inherent strain in the molecules. An unusual tendency for fragment ions to recyclize is supported by deuterium labeling results, high resolution mass measurements, metastable studies and comparison with model compounds. The mass spectra of the bicyclic ketones under investigation are considerably more complex than those of acyclic ketones.
Utilisation du 13C en Spectrométrie de Masse: Etude de la Fragmentation de Disaccharides
Authors: Bosso Claude , Taravel François , Ulrich Jacques , Vignon Michel 
Published: May 2005

AbstractUn ensemble de 29 dérivés disaccharidiques dans la série du D‐glucose et présentant des liaisons glycosidiques α‐ et β‐ (1 → 3), α‐ et β‐ (1 → 4) et β‐ (1 → 6) a été analysé par spectrométrie de masse en impact électronique. Outre les mécanismes déjà connus le marquage au 13C de quelques composés conduit à proposer un mécanisme de formation pour un ion c formé de l'unité réductrice B avec rétention de C‐1′ de l'unité non réductrice A d'où part la fragmentation et le réarrangement.
Hydrogen rearrangement in the mass spectra of (E)‐1‐alkylsulfonyl‐2‐phenylethenes
Authors: Liu Lilian Kao , Hong C. T. 
Published: May 2005

AbstractA novel McLafferty‐type rearrangement has been found to be the most facile fragmentation of (E)‐1‐alkylsulfonyl‐2‐phenylethenes and the migratory aptitudes for different kinds of hydrogen involved has been qualitatively estimated as benzylic ∼tertiary>secondary>primary.
Evidence for a [2+4] cycloaddition in the ion‐molecule reaction of ionized 1,3‐butadiene with vinyl ethyl (methyl) ether in the gas phase
Authors: Van Doorn R. , Nibbering N. M. M. , Ferrer‐Correia A. J. V. , Jennings K. R. 
Published: May 2005

AbstractBy use of deuterium labelling it is shown that the radical cation of 1,3‐butadiene reacts with vinyl methyl (or ethyl) ether in the gas phase through a [2+4] cycloaddition reaction. This leads to an excited collision complex of ionized 4‐methoxy‐ (or ethoxy) cyclohexene, which expels mthanol (or ethanol) through a 1,3 elimination, as does 4‐methoxycyclohexene itself upon electron impact. The spectrum of daughter ions produced by collision induced decomposition of the resulting ion with m/e 80 has been compared with spectra produced by the collision induced decompositions of the m/e 80 ions given by 1,3‐cyclohexadiene, 1,4‐cyclohexadiene, 1,3,5‐hexatriene and the [M–MeOH]\documentclass{article}\pagestyle{empty}\begin{document}$\mathop +\limits_\cdot$\end{document} ion from 4‐methoxycyclohexene.
Negative ion chemical ionization mass spectrometric studies of tetradentate schiff base coordination compounds. Fluorinecontaining reagent gases
Authors: Baumgartner Erwin , Dillard John G. 
Published: May 2005

AbstractNegative ion mass spectra using chemical ionization conditions have been measured for a series of tetradentate Schiff base corrdination compounds of Co(II), Ni(II) and Cu(II). Fluorine‐containing reagent gases CF4, SO2F2 and SF6 have been used. The formation of molecular negative ions for the complexes is dependent on the reagent gas used. The secondary ions detected are produced by incorporation of CF3, F and F2 species into the coordination compounds.
Ionen‐Cyclotron‐Resonanz‐Messungen von Ion/Molekül‐Reaktionen bei Chinonen
Authors: Suhr Harald , Szabo Andras , Miller Lary L. 
Published: May 2005

AbstractDie ICR‐Spektren von p‐Benzochinon, Methyl‐p‐benzochinon, Durochinon und Tetrafluor‐p‐benzochinon stimmen bei 10−6 Torr weitgehend mit den normalen Massenspektren überein, zeigen jedoch oberhalb von 10−5 Torr zahlreiche Signale für Produktionen. Doppelresonanzmessungen ergaben, daß alle Produktionen durch Analagerung des Molekularions bzw. eines Fragmentions an ein neutrales Chinonmolekül gebildet werden und zwar meistens unter Abspaltung von Kohlenmonoxyd.