Mass spectra of organometallic compounds: XIV—Some monometallic olefing manganese tricarbonyl derivatives

The metastable ion supported fragmentation process in the mass spectra of the cyclohexadienyl derivative C₆H₇Mn(CO)₃, the cycloheptadienyl derivative C₇H₉Mn(CO)₃, the 1,2,3,4,5-and 1,2,3,5,6-pentahaptocyclootadienyl derivatives C₈H₁₁Mn(CO)₃, the cyclooctatrienyl derivative C₈H₉Mn(CO)₃ and the substituted cyclopentadienyl derivative (CH₃)₂NCH₂C₅H₄Mn(CO)₃, are described. Losses of carbonyl groups, generally stepwise, from the molecular ions to give the corresponding [M – 3CO]⁺· ions are first observed. Further fragmentation of the carbonyl-free [M – 3CO]⁺· ions can involve a variety of processes such as the following: (a) elimination of a neutral manganese atom to give a hydrocarbon fragment; (b) elimination of a neutral hydrocarbon fragment to give an [MnH]⁺· ion; (c) dehydrogenation; (d) elimination of a 2-carbon C₂H₂ or C₂H₄ fragment; (e) elimination of a C₃H₄ or C₃H₆ fragment as a neutral species when it is bridging two carbon atoms bonded to manganese, as in C₈H₉Mn(CO)₃ and 1,2,3,4,5,h⁵-C₈H₁₁Mn(CO)₃, respectively. Fragmentation of the [M – 3CO]⁺· ion in (CH₃)₂NCH₂C₅H₄Mn(CO)₃ presents the following additional features: (a) elimination of C₆H₆ with a nitrogen shift from carbon to manganese; (b) elimination of a neutral dimethylamino fragment to give [C₆H₆Mn]⁺·, which then loses neutral C₆H₆, C₆H₅ or Mn fragments and thus is formulated tentatively as [(fulvene)Mn]⁺· or [C₆H₅MnH]⁺· rather than [(benzene)Mn]⁺·.     

A mass spectral study of 1-(aryldimethylsilyl)-2-propanones and their isomeric 2-(aryldimethylsiloxy)-1-propenes

The mass spectra of a series of β-ketosilanes, p-Y? C₆H₄Me₂SiCH₂C(O)Me and their isomeric silyl enol ethers, p-Y? C₆H₄Me₂SiOC(CH₃)?CH₂, where Y = H, Me, MeO, Cl, F and CF₃, have been recorded. The fragmentation patterns for the β-ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [M? Me·]⁺, [M? C₆H₄Y·]⁺, [M? Me₂SiO]⁺˙, [M? C₃H₄]⁺˙, [M? HC?CCF₃]⁺˙, [Me₂SiOH]⁺˙ and [C₃H₆O]⁺˙ Apparently, upon electron bombardment the β-ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [M? Me₂SiO]⁺˙ and [Me₂SiOH]⁺˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.     

Thermospray mass spectrometry of N-methylcarbamates

The thermospray mass spectrometry (TSP/MS) of five N-methylcarbamates is presented. This is the first time that ions other than [M + H]⁺ and [M + NH₄]⁺ have been reported using positive TSP/MS. Protonation of ROCONHCH₃ yields the [CH₃NH₂CO]^+· ion, with formation of the ion–molecule adduct [ROCONHCH₃ · CH₃NH₂CO]^+· through elimination of CO^+· from [CH₃NH₂CO]^+·, and the adduct [M + 75]^+·, [ROCONHCH₃ · OCONH₂CH₃]^+·, is also obtained.     

Electron ionization mass spectra of novel 2,3:4,5-bis-O-(1-methylethylidene)-β-D-fructopyranose derivatives and related sugar sulfamates

The electron-impact (EI) mass spectral fragmentation of ten bis-O- (1-methylethylidene)fructopyranose derivatives and three related sugar sulfamates were investigated. In particular, 2,3:4,5-bis-O - (1-methylethylidene)-β-D-fructopyranose sulfamate (topiramate), a potent anticonvulsant, was examined in greater detail. The fragmentation of the 2,3:4,5-bis-O-(1-methylethylidene) fructopyranose derivatives in general was not very dependent on the nature of substitution; the mechanisms of the common and unique fragmentation patterns are presented. These compounds showed characteristic peaks at m/z [M – 15]⁺, [M – 15 – 58]⁺, [M – 15 – 58 – 60]⁺, [M ? CH₂X]⁺ and [M ? CH₂X – 58]⁺ where X = OSO₂NR₂ (R ? H, CH₃, and/or Ph), OC (O)NHR, NH₂, CI and OH. The fragmentation of isomeric bis-O-(1-methylethylidene) derivatives of aldopyranose, ketopyranose and ketofuranose sulfamates was also investigated. The results indicate that isomeric sugar sulfamates can be easily distinguished in the EI mode. Key fragmentation pathways are discussed for these compounds.     

Atmospheric pressure chemical ionization and fragmentation of aminomonosaccharides in H2O and D2O

Aminomonosaccharides (glucosamine, galactosamine, and mannosamine) in H₂O and D₂O were ionized by atmospheric pressure chemical ionization (APCI) and their fragmentation patterns were investigated to identify them. All the aminomonosaccharides showed the same fragment ions but their relative ion intensities were different. Major product ions generated in H₂O were [M + H]⁺, [M + H – H₂O]⁺, and [2M + H – 3H₂O]⁺, while in D₂O were [M_D6 + D]⁺, [M_D6 + D – D₂O]⁺, and [2M_D6 + D – D₂O – 2HDO]⁺. At a high fragmentor voltage above 120 V, the relative ion intensities of the major product ions showed different trends according to the aminomonosaccharides. For the use of H₂O as solvent and eluent, the order of the ion intensity ratio of [M + H – H₂O]⁺/[2M + H – 3H₂O]⁺ was galactosamine > mannosamine > glucosamine. When using D₂O as solvent and eluent, the order of the ion intensity ratios of [M_D6 + D – D₂O]⁺/[M_D6 + D]⁺ and [2M_D6 + D – D₂O – 2HDO]⁺/[M_D6 + D]⁺ was mannosamine > galactosamine > glucosamine. It was found that glucosamine, galactosamine, and mannosamine could be distinguished by the specific trends of the major product ion ratios in H₂O and D₂O. Copyright © 2009 John Wiley & Sons, Ltd.     

Mass spectrometry of 3-substituted 4-hydroxyisoquinolines and their derivatives

Under electron impact, 3-aryl-4-hydroxyisoquinolines form [M – H]⁺, [M – CO]⁺ and [M – H – CO]⁺ ions with a subsequent elimination of HCN or CH₃CN. A cyclic structure for the [M – H]⁺ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH₃?, as well as H?; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]⁺, [M – OH]⁺ and [M – CH₅?]⁺ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.     

Gaseous [C2H3O]+ ions

[C₂H₃O]⁺ ions with the initial structures [CH₃CO]⁺, and [CH₂CHO]⁺ cannot be distinguished on the basis of their collisional activation spectra, demonstrating that these isomers interconvert at energies below their threshold for decomposition. Self-protonation of ketene leads to the [CH₃CO]⁺ ion, while the [C₂H₃O]⁺ ion generated from glycerol most probably has the structure of an oxygen protonated ketene [CH₂?C?OH]⁺.     

[C]+· and [CH]+ from doubly charged ions formed from malononitrile

The metastable ions [M]²⁺, [M – H]²⁺· and [M – H₂]²⁺ from malononitrile fragment by loss of [CH]⁺, [C]⁺· and [C]⁺·, respectively. The reaction of the molecular ion involves the methylene and nitrile carbon atoms in the statistical probability ratio, while that of [M – H]²⁺· involves exclusively the nitrile carbon and that of [M ? H₂]²⁺ involves an approximately equal contribution, from both sources. It is suggested that the metastable molecular ion fragments through a bipyrimidal intermediate.     

Loss of methyl from [H2CC(OH)?CH3]+˙ ions prepared by electron impact ionization of unstable 2-hydroxypropene

Unstable 2-hydroxpropene was prepared by retro-Diels-Alder decomposition of 5-exo-methyl-5-norbornenol at 800°C/2 × 10^?6 Torr. The ionization energy of 2-hydroxypropene was measured as 8.67±0.05 eV. Formation of [C₂H₃O]⁺ and [CH₃]⁺ ions originating from different parts of the parent ion was examined by means of ¹³C and deuterium labelling. Threshold-energy [H₂C?C(OH)? CH₃]^+˙ ions decompose to CH₃CO⁺+CH₃^˙ with appearance energy AE(CH₃CO⁺) = 11.03 ± 0.03 eV. Higher energy ions also form CH₂?C?OH⁺ + CH₃ with appearance energy AE(CH₂?C?OH⁺) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C₂H₃O]⁺ ions containing the original methyl group and [CH₃]⁺ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate-determining isomerization [H₂C?C(OH)? CH₃]^+˙ →[CH₃COCH₃]^+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.     

Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)?CHCH2]+˙ and [CH2CH?CHCH(OH)]+˙ and their relationship with their keto counterparts

The [C₄H₆O]^+˙ ion of structure [CH₂?CHCH?CHOH]^+˙ (a) is generated by loss of C₄H₈ from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔH_f of [CH₂?CHCH?CHOH]^+˙ was estimated to be 736 kJ mol^?1. The isomeric ion [CH₂?C(OH)CH?CH₂]^+˙ (b) was shown to have ΔH_f, ? 761 kJ mol^?1, 54 kJ mol^?1 less than that of its keto analogue [CH₃COCH?CH₂]^+˙. Ion [CH₂?C(OH)CH?CH₂]^+˙ may be generated by loss of C₂H₄ from ionized hex-1-en-3-one or by loss of C₄H₈ from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C₄H₆O]^+˙ ion generated by loss of C₂H₄ from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH₂?CHCH?CHOH]^+˙ and [CH₂?C(OH)CH?CH₂]^+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH₃˙ and CO, [CH₂?CHCH?CHOH]⁺˙ and [CH₂?C(OH)CH?CH₂]^+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C₄H₆O]^+˙ ion [CH₂?C?CHCH₂OH]^+˙ are also reported.     

Functionalised Tris(pyrazolyl)methane Ligands and Re(CO)3 Complexes Thereof

The synthesis of new tripodal nitrogen ligands derived from tris(pyrazolyl)methane (Tpm^R, R = H, tBu, Ph in 3‐position) is described. After deprotonation of the parent tris(pyrazolyl)methane Tpm^R, the carbanion reacts readily with ethylene oxide to yield the 3,3,3‐tris(3′‐substituted pyrazolyl)propanol ligands[(3‐Rpz)₃CCH₂CH₂OH, R = H, tBu, Ph, 1a – c ]. These ligands can be easily derivatised at the alcohol function. Microwave‐assisted reactions of these ligands and [Re(CO)₅Br] yields the complex [( 1a )Re(CO)₃]Br ( 4 ) in the case of ligand 1a , whereas in the case of the substituted ligands 1b and 1c degradation was observed. The degradation products are identified as [(Hpz^R)₂Re(CO)₃Br] [R = tBu ( 7b ), Ph ( 7c )]. These complexes were also prepared directly from [Re(CO)₅Br] and the corresponding pyrazoles by microwave‐assisted synthesis. The Re(CO)₃ complexes 4 and [( 1a )Re(CO)₃]OTf ( 5 ) are water‐soluble. The structures of 5· H₂O and [{(pz)₃CCH₂CH₃}Re(CO)₃]OTf · 1.5H₂O · ¹/₂CH₃CN ( 6· 1.5H₂O · ¹/₂CH₃CN) as well as the structure of 7b have been elucidated by X‐ray crystallography.     

Mass spectrometric monitoring of oxidation of aliphatic C6–C8 hydrocarbons and ethanol in low pressure oxygen and air plasmas

Experimental and theoretical studies on the oxidation of saturated hydrocarbons (n‐hexane, cyclohexane, n‐heptane, n‐octane and isooctane) and ethanol in 28 Torr O₂ or air plasma generated by a hollow cathode discharge ion source were made. Ions corresponding to [M + 15]⁺ and [M + 13]⁺ in addition to [M ? H]⁺ and [M ? 3H]⁺ were detected as major ions where M is the sample molecule. The ions [M + 15]⁺ and [M + 13]⁺ were assigned as oxidation products, [M ? H + O]⁺ and [M ? 3H + O]⁺, respectively. By the tandem mass spectrometry analysis of [M ? H + O]⁺ and [M ? 3H + O]⁺, H₂O, olefins (and/or cycloalkanes) and oxygen‐containing compounds were eliminated from these ions. Ozone as one of the terminal products in the O₂ plasma was postulated as the oxidizing reagent. As an example, the reactions of C₆H₁₄^+? with O₂ and of C₆H₁₃⁺ (CH₃CH₂CH⁺CH₂CH₂CH₃) with ozone were examined by density functional theory calculations. Nucleophilic interaction of ozone with C₆H₁₃⁺ leads to the formation of protonated ketone, CH₃CH₂C(=OH⁺)CH₂CH₂CH₃. In air plasma, [M ? H + O]⁺ became predominant over carbocations, [M ? H]⁺ and [M ? 3H]⁺. For ethanol, the protonated acetic acid CH₃C(OH)₂⁺ (m/z 61.03) was formed as the oxidation product. The peaks at m/z 75.04 and 75.08 are assigned as protonated ethyl formate and protonated diethyl ether, respectively, and that at m/z 89.06 as protonated ethyl acetate. Copyright © 2016 John Wiley & Sons, Ltd.     

Bridgehead nitrogen heterocycles—II: The mass spectra of some pyrazolo[1,5-a]pyridines

Pyrazolo[1,5-a]pyridine undergoes fragmentation upon electron-impact by loss of HCN or C₂H₂N·. In the 2,3-dimethyl derivative loss of HCN and CH₃CN were both observed from the [M – 1]⁺ ion and, in the 3-methyl-2-phenyl derivative, loss of PhCN occurred from the corresponding [M – 1]⁺ ion. Loss of methyl and phenyl radicals was also observed. In 3-acetyl-2-methyl and 3-benzoyl-2-phenyl derivatives, characteristic losses of the CH₃CO· and PhCO· groups were noted. The introduction of a 7-methyl substituent into the six-membered ring had little effect on the fragmentation pattern.     

Untersuchungen in der Thiazolreihe. III—massenspektrometrische Untersuchung von 2-Amino-3-hydroxythiazoliumchloriden

The mass spectrometric decomposition of 2-aminothiazole-3-oxides is characterised by the abstraction of O and OH out of the molecule ion. Distinct differences between 4-alkyl and 4-aryl derivatives as well as defined dependence of the [M – O]⁺·: [M – OH]⁺ ratio on the substituents are interpreted by a stabilisation of the [M – O]⁺·: radical cation through aromatic substitution. The effects of temperature suggest an equilibrum between tautomers in the inlet system.     

Why Are B ions stable species in peptide spectra?

Protonated amino acids and derivatives RCH(NH₂)C(+O)X · H⁺ (X = OH, NH₂, OCH₃) do not form stable acylium ions on loss of HX, but rather the acylium ion eliminates CO to form the immonium ion RCH = NH ₂ ⁺ . By contrast, protonated dipeptide derivatives H₂NCH(R)C(+O)NHCH(R′)C(+O)X · H⁺ [X = OH, OCH₃, NH₂, NHCH(R″)COOH] form stable B₂ ions by elimination of HX. These B₂ ions fragment on the metastable ion time scale by elimination of CO with substantial kinetic energy release (T _1/2 = 0.3–0.5 eV). Similarly, protonated N-acetyl amino acid derivatives CH₃C(+O)NHCH(R′)C(+O)X · H⁺ [X = OH, OCH₃, NH₂, NHCH(R″)COOH] form stable B ions by loss of HX. These B ions also fragment unimolecularly by loss of CO with T _1/2 values of ～ 0.5 eV. These large kinetic energy releases indicate that a stable configuration of the B ions fragments by way of activation to a reacting configuration that is higher in energy than the products, and some of the fragmentation exothermicity of the final step is partitioned into kinetic energy of the separating fragments. We conclude that the stable configuration is a protonated oxazolone, which is formed by interaction of the developing charge (as HX is lost) with the N-terminus carbonyl group and that the reacting configuration is the acyclic acylium ion. This conclusion is supported by the similar fragmentation behavior of protonated 2-phenyl-5-oxazolone and the B ion derived by loss of H-Gly-OH from protonated C₆H₅C(+O)-Gly-Gly-OH. In addition, ab initio calculations on the simplest B ion, nominally HC(+O)NHCH₂CO⁺, show that the lowest energy structure is the protonated oxazolone. The acyclic acylium isomer is 1.49 eV higher in energy than the protonated oxazolone and 0.88 eV higher in energy than the fragmentation products, HC(+O)N⁺H = CH₂ + CO, which is consistent with the kinetic energy releases measured.     

A quantum chemical consideration of ligand exchange in palladium(ii) aqueous and chloride complexes

The behavior of potassium tetrachloropalladate(II) in media simulating biological fluids has been studied. In aqueous solutions of NaCl, the aquation rate is higher than the rate of chloro ligand introduction into the internal coordination sphere of palladium. In HCl solutions, on the contrary, the process of palladium chloro complex formation predominates. The latter is apparently due to protonation of water molecules composing aqua complexes. By means of the ZINDO/1 method, the substitution of ligands – water molecules and hydronium ion – in planar complexes of palladium(II) by chloride ion has been investigated. All complexes containing H₂O and H₃O⁺ ligands, other than [Pd(H₂O)₄]²⁺, have intramolecular hydrogen bonds. In [Pd(H₂O)₃(H₃O)]³⁺ and trans-[Pd(H₂O)₂(H₃O)Cl]²⁺, a “non-classic” symmetric hydrogen bond O ··· H ··· O is established (ZINDO/1, RHF/STO-6G*). By the first three steps the substitution of hydronium ion in the internal sphere of palladium atom is more favorable thermodynamically, compared to water molecules. Logarithms of stepwise stability constants of palladium(II) chloride complexes correlate linearly to enthalpies (ZINDO/1, PM3) of water substitution by chloride ion.     

Protonated silanoic acid HSi(OH)2+ and its neutral counterpart: a tandem mass spectrometric and CBS-QB3 computational study

Protonated silanoic acid, HSi(OH)₂⁺, 1a ⁺, is cleanly generated by the dissociative electron ionization of triethoxysilane, HSi(OC₂H₅)₃, and tetraethoxysilane, Si(OC₂H₅)₄. This follows from tandem mass spectrometric experiments and CBS-QB3 model chemistry calculations. The calculations predict that 1a ⁺ (ΔH_f(298 K) = 205 kJ mol⁻¹) is separated by high barriers from its isomers HOSiOH₂⁺, 1b ⁺ and HSi(O)OH₂⁺, 1c ⁺. Low-energy (metastable) ions 1a ⁺ dissociate by loss of H₂O via the pathway 1a ⁺ → 1b ⁺ → SiOH⁺ + H₂O. Analysis of the metastable peak for this process confirms that the isomerization step 1a ⁺ → 1b ⁺ is rate determining. The calculations further predict that the incipient ions 1b ⁺ communicate via a low barrier with the proton-bound dimer SiO···H···OH₂⁺, 1d ⁺. This dimer ion is much lower in energy than its counterpart OSi···H···OH₂⁺, 1e ⁺, which is calculated to be only marginally stable. A comparison of the potential energy diagram for the silicon-containing ions 1a ⁺– 1e ⁺ with that of their carbon analogues reveals that the dissociation chemistries of HSi(OH)₂⁺ and HC(OH)₂⁺ are only superficially similar. Neutralization–reionization experiments confirm the theoretical prediction that the HSi(OH)₂^• radical (ΔH_f(298 K) = −455 kJ mol⁻¹) is a stable species in the rarefied gas phase. However, owing to a mismatch of Franck–Condon factors a large fraction of the neutralized ions dissociates by loss of H^• yielding Si(OH)₂. Copyright © 2004 John Wiley & Sons, Ltd.     

Charakterisierung von Distorsionsisomeren der Anionen Pentacyano-oxo-molybdat(IV) sowie Tetracyano-oxo-aqua-molybdat(IV) im festen Zustand. Kristallstrukturen von [(C6H5)4P]3[MoO(CN)5] · 7 H2O(grün), [(C6H5)4As]2 [MoO(OH2)(CN)4] · 4 H2O (blau) und [(C6H5)4P]2[MoO(OH2)(CN)4] · 4 H2O (grün)

Characterization of Distortional Isomers of the Anions Pentacyano-oxo-molybdate(IV) and of Tetracyano-aqua-oxo-molybdate(IV) in the Solid State. Crystal Structures of [(C₆H₅)₄P]₃[MoO(CN)₅] · 7 H₂O (green), [(C₆H₅)₄As]₂[MoO(OH₂)(CN)₄] · 4 H₂O (blue), and [(C₆H₅)₄P]₂[MoO(OH₂) (CN)₄] · 4 H₂O (green) Preparation of a series of salts containing the new pentacyano-oxo-molybdate(IV) anion is described: Cs₂H[MoO(CN)₅] (blue), [(CH₃)₄N]₂H[MoO(CN)₅] · 2 H₂O (blue) and [Cr(en)₃] [MoO(CN)₅] · 4 H₂O (green). The green [(C₆H₅)₄P]₃[MoO(CN)₅] · 7 H₂O crystallizes triclinic in the space group P1 . The molybdenum(IV) center is in an pseudo-octahedral environment of a terminal oxo-group (d(Mo?O); 1.705(4) Å), a CN^? group in the trans-position (d(Mo? C): 2.373(6) Å), and four equatorial CN^? groups (averaged d(Mo? C): 2.178 (Å). The blue and green salts exhibit v(Mo?O) stretching frequencies at 948 cm^?1 and 920 cm^?1, respectively. Blue and green salts containing the [MoO(OH₂)(CN)₄]^2? anion and [(C₆H₅)₄P]⁺ or [(C₆H₅)₄As]⁺ cations have been prepared and characterized by single crystal crystallography. [(C₆H₅)₄P]₂[MoO(OH₂)(CN)₄] · 4 H₂O (green) and [(C₆H₅)₄As]₂[MoO(OH₂)(CN)₄] · 4 H₂O (blue) crystallize monoclinic in the space group C—P2₁/n. They are considered to be distortional isomers of the complex anion: the green species has a Mo?O bond distance of 1.72(2) Å whereas for the blue species d(Mo?O) = 1.60(2) Å is found; the corresponding v(Mo?O) frequencies are at 920 cm^?1 and 980 cm^?1.     

Stereochemical applications of mass spectrometry. 3—Energy dependence of the fragmentation of stereoisomeric methylcyclohexanols

Breakdown graphs have been constructed from charge exchange data for the epimeric 2-methyl-, 3-methyl- and 4-methyl-cyclohexanols. Although the breakdown graphs for epimeric pairs are essentially identical above ～12 eV recombination energy, significant differences are observed for the epimeric 2-methyl- and 4-methyl-cyclohexanols at low internal energies. For the 2-methylcyclohexanols the ratio ([M? H₂O]^+·/[M]^+·)_cis/([M? H₂O]^+·/[M]^+·)_trans is 3.2 in the [C₆F₆]^+· charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis-1,4-H₂O elimination for the cis epimer. The breakdown graph for trans-4-methylcyclohexanol shows a sharp peak in the abundance of the [M? H₂O]^+· ion at ～10 eV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attributed to the stereospecific cis-1,4-elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [C₆F₆]^+· charge exchange mass spectra the ([M? H₂O]^+·/[M]^+·)_trans/([M? H₂O]^+·/[M]^+·)_cis ratio is ～24, compared to the value of 13 observed in the 70 eV EI mass spectra. No differences are observed in either the metastable ion abundances or the associated kinetic energy releases for epimeric molecules.     

NEt4OH·4H2O containing infinite hydro­xide–water ribbons

In tetraethyl­ammonium hydro­xide tetrahydrate, C₈H₂₀N⁺·­OH^?·­4H₂O, the array of mirror symmetric NEt₄⁺ cations gives rise to a system of parallel channels which are filled with hydrogen‐bonded anionic ribbons. The central part of each ribbon is constituted by a [OH^?(HOH)_4/2] spiro‐chain, with each hydro­xide ion accepting four strong linear hydrogen bonds [d(O?O) between 2.692 (1) and 2.727 (1) Å] but donating none. Additional (two‐coordinate) H₂O mol­ecules bridge between the (four‐coordinate) H₂O mol­ecules of the spiro‐chain [d(O?O) between 2.831 (1) and 2.835 (1) Å].