Optimized NMR Experiments for the Isolation of I=1/2 Manifold Transitions in Methyl Groups of Proteins

Optimized NMR experiments are developed for isolating magnetization belonging to the I=1/2 manifolds of ¹³CH₃ methyl groups in proteins, enabling the manipulation of the magnetization of a ¹³CH₃ moiety as if it were an AX (¹H-¹³C) spin-system. These experiments result in the same ‘simplification’ of a ¹³CH₃ spin-system that would be obtained from the production of {¹³CHD₂}-methyl-labeled protein samples. The sensitivity of I=1/2 manifold-selection experiments is a factor of approximately 2 less than that of the corresponding experiments acquired on {¹³CHD₂}-labeled methyl groups. The methodology described here is primarily intended for small-to-medium sized proteins, where the losses in sensitivity associated with the isolation of I=1/2 manifold transitions can be tolerated. Several NMR applications that benefit from simplification of the ¹³CH₃ (AX₃) spin-systems are described, with an emphasis on the measurements of methyl ¹H-¹³C residual dipolar couplings in a {¹³CH₃}-methyl-labeled deletion mutant of the human chaperone DNAJB6b, where modulation of NMR signal intensities due to evolution of methyl ¹H-¹³C scalar and dipolar couplings follows a simple cosine function characteristic of an AX (¹H-¹³C) spin-system, significantly simplifying data analysis.     

Applications of NMR spectroscopy of chiral association complexes 5. Stereodynamics and diastereotopism in chiral 1,3-dienes \documentclass{article}\pagestyle{empty}\begin{document}${\rm HOCMe}_{\rm 2} \rlap{--} ({\rm CCl =\!= CCl\rlap{--})}_{\rm 2} {\rm X}$\end{document}

The barriers to partial rotation around the central single bond in chiral dienes \documentclass{article}\pagestyle{empty}\begin{document}${\rm HOCMe}_{\rm 2} \rlap{--} ({\rm CCl =\!= CCl\rlap{--})}_{\rm 2} {\rm X}$\end{document} have been determined by coalescence of either ¹H NMR signals (X = CH₂OCH₃) or ¹³C NMR signals (X = H). In the presence of the optically active shift reagent (+) ? Eu(hfbc)₃ all ¹H signals were split at temperatures where the interconversion of enantiomers is slow. The temperature dependence of these spectra also yielded free activation enthalpies for the enantiomerizations which were in agreement with the ones obtained without Eu(hfbc)₃. The assignment of the four methyl resonances appearing in the presence of (+) ? Eu(hfbc)₃ at low temperature was possible by gradually increasing the rate of enantiomerization or gradually replacing the optically active auxiliary compound by the racemic one.     

Yttrium Siloxide Complexes Bearing Terminal Methyl Ligands: Molecular Models for Ln−CH3 Terminated Silica Surfaces

Surface organometallic chemistry (SOMC) on silica materials is a prominent approach for the generation of highly active heterogenized polymerization catalysts. Despite advanced methods of characterization, the elucidation of the catalytically active surface species remains a challenging task. Alkylated rare‐earth metal siloxide complexes can be regarded as molecular models of respective covalently bonded alkylated surface species, primarily used for 1,3‐diene polymerization. Here, we performed both salt metathesis reactions of [Y(MMe₄)₃] (M = Al, Ga) with [K{OSi(OtBu)₃}] and alkylation reactions of [Y{OSi(OtBu)₃}₃]₂ with AlMe₃. The obtained complexes [Y(CH₃)[(AlMe₂){OSi(OtBu)₃}₂](AlMe₄)]₂, [Y(CH₃)[(AlMe₂){OSi(OtBu)₃}₂]‐{OSi(OtBu)₃}], [Y{OSi(OtBu)₃}₃(μ‐Me)Y(μ‐Me)₂Y{OSi(OtBu)₃}₂(AlMe₄)], and [Y(CH₃)(GaMe₄){OSi(OtBu)₃}]₂ represent rare examples of organoyttrium species with terminal methyl groups. The formation and purity of the mixed methyl/siloxy yttrium complexes could be enhanced by treating [Y(MMe₄)₃] with [K(MMe₂){OSi(OtBu)₃}₂]_n (M=Al: n=2; M=Ga: n=∞). Complexes [K(MMe₂){OSi(OtBu)₃}₂]_n were obtained by addition of [K{OSi(OtBu)₃}] to [Me₂M{OSi(OtBu)₃}]₂. Deeper insight into the fluxional behavior of the mixed methyl/siloxy yttrium complexes in solution was gained by ¹H and ¹³C NMR spectroscopic studies at variable temperature and ¹H–⁸⁹Y HSQC NMR spectroscopy.     

Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials

Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}₃] [when R = Me, Ar = 2‐C₅H₄N ( 1 ), 2‐C₄H₃O ( 2 ) or 2‐C₄H₃S ( 3 ); and when R = H, Ar = 2‐C₅H₄N ( 4 ), 2‐C₄H₃O ( 5 ) or 2‐C₄H₃S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. ¹H and ¹³C{¹H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by ²⁹Si{¹H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO_3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPrⁱ)₃ in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH₃)C₄H₃O}₃.Al(OPrⁱ)₃]. Spectroscopic techniques ¹H, ¹³C{¹H}, ²⁷Al{¹H} and ²⁹Si{¹H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m²/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(vinylpyrrolidone): Configurational assignments by one- and two-dimensional NMR spectroscopy

The configurational assignment of poly(vinylpyrrolidone) (PVP) prepared by peroxide-initiated solution polymerization was studied by the combination of one- and two-dimensional NMR spectroscopy. The broad and overlapping ¹H-NMR and ¹³C{¹H}-NMR spectra of PVP were assigned to the configurational triad, pentad (CH, ²CH₂, ³CH₂, and ⁴CH₂ regions), and tetrad (β-CH₂ region) sequences. The configurational assignments of the various carbon resonances were confirmed with the help of two-dimensional experiments such as heteronuclear single quantum correlation (HSQC), heteronuclear single quantum correlation–total correlation spectroscopy (2-D HSQC–TOCSY). The various geminal and vicinal couplings within the configurational sequences were assigned with the help of total correlation spectroscopy (TOCSY low mixing time). The propagation pathway was studied using the ¹³C{¹H}-NMR (carbonyl carbon) and ¹⁵N{¹H}-NMR spectra. The ¹⁵N{¹H} resonance signals were assigned to pentad-level configurational sequences. The results obtained by the analysis of the area under the resonance signals confirmed that poly(vinylpyrrolidone) obeys Bernoullian statistics. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3922–3928, 1999     

Anisole,acetophenone and benzoic acid methyl ester oriented in a nematic phase: Structure and internal motion

¹H-, ¹H? {²D}-, ²D- and ²D? {¹H}-N.m.r.-spectra were used in an investigation of the partially oriented molecules anisole, acetophenone and benzoic acid methyl ester. The phenyl ring geometries were found to deviate slightly from the regular hexagon. For anisole and acetophenone the measured couplings indicate a structure with the substituent group in the plane of the ring and one of the methyl protons pointing away from it. It is not possible, however, to draw further conclusions on the depths and shapes of the potentials hindering the internal motions. For benzoic acid methyl ester the measurements indicate that the dominant conformer is the one with the O? CH₃ axis approximately parallel to the effective molecular C₂-symmetry axis. Semiempirical MO calculations were found to provide reasonable molecular structures but no information on the potentials.     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

Solid‐State NMR Investigations on the Amorphous Network of Precursor‐Derived Si2B2N5C4 Ceramics

Employing a multitude of modern solid state NMR techniques including ¹³C{¹⁵N}REDOR NMR, ¹H–¹³C CP NMR, ¹¹B MQMAS NMR spectroscopic experiments, the structural organization of Si₂B₂N₅C₄ ceramic has been studied. The experiments were executed on double isotope enriched (¹³C, ¹⁵N) and natural isotope abundance Si₂B₂N₅C₄ ceramics. The materials were synthesized by aminolysis and subsequent pyrolysis of intermediate pre‐ceramic polymers that were obtained from the single source precursor TSDE, 1‐(trichlorosilyl)‐1‐(dichloroboryl)ethane (Cl₃Si–CH(CH₃)–BCl₂). The result of the ¹³C{¹⁵N} REDOR NMR spectroscopic experiment shows that carbon atoms are incorporated into the network by bridging to nitrogen, which already occurs during the polymerization step. Furthermore, the combined results of ¹¹B NMR and ¹¹B MQMAS NMR indicate that boron atoms may also be connected to carbon in addition to nitrogen.     

Reactivity of cationic methyl rhodium(III) complexes cis-[Rh(β-diket)(PPh3)2(CH3)(CH3CN)][BPh4] toward ligands of different character: pyridine, carbon monoxide, and triphenylphosphine

Cationic methyl complex of rhodium(III), cis-[Rh(Acac)(PPh₃)₂(CH₃)(Py)][BPh₄] (1) as a single isomer with Py in the trans to PPh₃ position, is formed upon the reaction of cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] with pyridine in methylene chloride solution.Complex 1 was characterized by elemental analysis and by ³¹P{¹H} and ¹H NMR spectra.Cationic pentacoordinate acetyl complexes, trans-[Rh(Acac)(PPh₃)₂(COCH₃)][BPh₄] (2) and trans-[Rh(BA)(PPh₃)₂(COCH₃)][BPh₄] (3), are prepared by action of carbon monoxide on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄], respectively, in methylene chloride solutions.Complexes 2 and 3 were characterized by elemental analysis and by IR, ³¹P{¹H}, ¹³C{¹H} and ¹H NMR. According to NMR data, 2 and 3 in solution are non-fluxional trigonal bipyramids with β-diketonate and acetyl ligands in the equatorial plane and axial phosphines.In solutions, 2 and 3 gradually isomerize into octahedral methyl carbonyl complexes trans-[Rh(Acac)(PPh₃)₂(CO)(CH₃)][BPh₄] (4) and trans-[Rh(BA)(PPh₃)₂(CO)(CH₃)][BPh₄] (5), respectively.Complexes 4 and 5 were characterized by IR, ³¹P{¹H}, ¹³C{¹H} and ¹H NMR, without isolation.Upon the action of PPh₃ on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)] [BPh₄], reductive elimination of the methyl ligand as a phosphonium salt, [CH₃PPh₃][BPh₄], occurs to give square planar rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and[Rh(BA)(PPh₃)₂], respectively. The reaction products were identified in the reaction mixtures by ³¹P{¹H} and ¹H NMR.     

Poly(acrylonitrile‐co‐methyl methacrylate‐co‐methyl acrylate): Synthesis and stereosequence distribution analysis by 2D NMR

Terpolymers of acrylonitrile (A), methyl methacrylate (B), and methyl acrylate (M) were synthesized under optimized atom transfer radical polymerization conditions using 2‐bromopropionitrile as an initiator and CuBr/dinonyl bipyridine as a catalyst. Variation of the feed composition led to terpolymers with different compositions. Composition of synthesized terpolymers were calculated from quantitative ¹³C{¹H} NMR spectra. Number average molecular weight and polydispersity index were determined by gel permeation chromatography. The overlapping and broad signals of the terpolymers were assigned completely to various compositional and configurational sequences by correlation of one‐dimensional ¹H, ¹³C{¹H}, and distortionless enhancement by polarization transfer and two‐dimensional heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY). 2D HSQC NMR study shows one to one correlation between carbon and proton signals, while 2D TOCSY spectra were used to confirm 1, 2 bond geminal couplings between nonequivalent protons of same methylene group. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 25–37, 2009     

Synthesis and Characterization of trans‐PdII Trimethylsilylchalcogenolates

The trans‐bis(trimethylsilyl)chalcogenolate palladium complexes, trans‐[Pd(ESiMe₃)₂(PnBu₃)₂] [E = S ( 1 ) and Se ( 2 )] were synthesized in good yields and high purity by reacting trans‐[PdCl₂(PBu₃)₂] with LiESiMe₃ (E = S, Se), respectively. These complexes were characterized by ¹H, ¹³C{¹H}, ³¹P{¹H} (and ⁷⁷Se{¹H}) NMR spectroscopy and single‐crystal X‐ray analysis. The reaction of 2 with propionyl chloride led to the formation of trans‐[Pd(SeC(O)CH₂CH₃)₂(PnBu₃)₂] ( 3 ), a trans‐bis(selenocarboxylato) palladium complex and thus established a new method for the formation of this type of complex. Complex 3 was characterized by ¹H, ¹³C{¹H}, ³¹P{¹H} and ⁷⁷Se{¹H} NMR spectroscopy and a single‐crystal X‐ray structure analysis.     

Methoxy and Methyl Group Rotation: Solid‐State NMR 1H Spin‐Lattice Relaxation,Electronic Structure Calculations,X‐ray Diffractometry,and Scanning Electron Microscopy

We report solid‐state ¹H nuclear magnetic resonance (NMR) spin‐lattice relaxation experiments, X‐ray diffractometry, field‐emission scanning electron microscopy, and both single‐molecule and cluster ab initio electronic structure calculations on 1‐methoxyphenanthrene ( 1 ) and 3‐methoxyphenanthrene ( 2 ) to investigate the rotation of the methoxy groups and their constituent methyl groups. The electronic structure calculations and the ¹H NMR relaxation measurements can be used together to determine barriers for the rotation of a methoxy group and its constituent methyl group and to develop models for the two coupled motions.     

Reaction of hydrogen atoms with dimethyldisulfide

Hydrogen atoms, generated by the mercury (³P₁) sensitization of H₂, were allowed to react with dimethyldisulfide in the temperature range of 25–155°C. The only retrievable product is methanethiol, formed in the primary metathetical reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} + {\rm CH}_3 {\rm SSCH}_3 {\rm CH}_3 {\rm SH} + {\rm CH}_3 {\rm S} $\end{document}. The intermediacy of thiyl radicals was clearly demonstrated in experiments carried out in the presence of ethylene where one of the major products detected was ethyl methyl sulfide, formed via CH₃S + C₂H₅ → CH₃SC₂H₅. The major fate of the CH₃S radical is recombination and disproportionation, and the yield of methanethiol formed via disproportionation contributes less than 5% to the total thiol yield. The rate coefficient of step 1, from competition with the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H} + {\rm C}_{\rm 2} {\rm H}_{\rm 4} {\rm C}_{\rm 2} {\rm H}_5 $\end{document}, is k₁ = (5.7 ± 1.2) × 10¹² exp[? (100 ± 100)/RT] cm³/mol sec.     

Complete spectral assignments of methacrylonitrile-styrene-methyl methacrylate terpolymers by 2D NMR spectroscopy

Methacrylonitrile-styrene-methyl methacrylate (N/S/M) terpolymers of different monomer concentrations were prepared by bulk polymerization. The terpolymer compositions were determined by quantitative ¹³C{¹H} NMR spectra and compared with those calculated by Goldfinger's equation using comonomer reactivity ratios: r_NS=0.30, r_SN=0.45; r_NM=0.91, r_MN=0.88; r_SM=0.52, r_MS=0.47. The overlapping and complex ¹³C{¹H} and ¹H NMR spectra of the terpolymers were assigned with the help of distortionless enhancement by polarization transfer and two-dimensional (2D) ¹³C-¹H heteronuclear single quantum coherence experiments. The various vicinal and geminal couplings between the protons in the polymer chains can be seen in the 2D total correlated spectroscopy experiments.     

Methyl thiirane: Kinetic gas-phase titration of sulfur atoms in SX OY systems

The reaction SO + SO →l S + SO₂(2) was studied in the gas phase by using methyl thiirane as a titrant for sulfur atoms. By monitoring the C₃H₆ produced in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm S} + {\rm CH}_3\hbox{---} \overline {{\rm CH\hbox{---}CH}_2\hbox{---} {\rm S}} \to {\rm S}_2 + {\rm C}_3 {\rm H}_6 (7) $\end{document}, we determined that k₂ ? 3.5 × 10^?15 cm³/s at 298 K.     

Novel D- and T-functionalized Polysiloxane Matrices for Reactions in Interphases

New hydrocarbon bridged co-condensation agents of the type RSi(OMe)₂(CH₂)_zC₆H₄(CH₂)_z(OMe)₂SiR { 3[Ph(1,4-C₃D⁰)₂] , z = 3, R = Me; 3[Ph(1,4-C₃T⁰)₂] , z = 3, R = OMe; 4[Ph(1,4-C₃D⁰)₂] , z = 4, R = Me} were synthesized by hydrosilylation of the corresponding α,ω-dienes CH₂=CH–(CH₂)_z–2–C₆H₄–(CH₂)_z–2–CH=CH₂ [z = 3 ( 1 ), 4 ( 2 )] with HSiR(OMe)₂ (R = Me, OMe). These silane monomers were sol-gel processed, partially with MeSi(OMe)₃ ( T ⁰) to give the polysiloxanes 3 a , 3 b , 4 c , 3 d , 3 e , 4 f , and 3 ab (Table 1, Schemes 2 and 3); D = D type silicon atom (two oxygen neighbors), T = T type of silicon atom (three oxygen neighbors). The relative amounts of T and D silyl species and the degrees of condensation were determined by ²⁹Si and ¹³C CP/MAS NMR spectroscopic investigations. ²⁹Si and ¹³C CP/MAS NMR relaxation time studies (T_SiH, T_CH, T_1ρH), and 2 D WISE NMR experiments were applied to get knowledge about the polymer dynamics. For the first time protons of such polysiloxane systems were detected by ¹H SPE/MAS NMR measurements in suspension. Mobility studies were carried out in different solvents. Furthermore the swelling capacities of the polymers 3 a , 3 b , and 4 c in different solvents and the BET surface areas of all materials were investigated. SEM micrographs show the morphology of 3 a and 3 b .     

Fast Acquisition of Proton-Detected HETCOR Solid-State NMR Spectra of Quadrupolar Nuclei and Rapid Measurement of NH Bond Lengths by Frequency Selective HMQC and RESPDOR Pulse Sequences

Fast magic-angle spinning (MAS), frequency selective (FS) heteronuclear multiple quantum coherence (HMQC) experiments which function in an analogous manner to solution SOFAST HMQC NMR experiments, are demonstrated. Fast MAS enables efficient FS excitation of ¹H solid-state NMR signals. Selective excitation and observation preserves ¹H magnetization, leading to a significant shortening of the optimal inter-scan delay. Dipolar and scalar ¹H{¹⁴N} FS HMQC solid-state NMR experiments routinely provide 4- to 9-fold reductions in experiment times as compared to conventional ¹H{¹⁴N} HMQC solid-state NMR experiments. ¹H{¹⁴N} FS resonance-echo saturation-pulse double-resonance (RESPDOR) allowed dipolar dephasing curves to be obtained in minutes, enabling the rapid determination of NH dipolar coupling constants and internuclear distances. ¹H{¹⁴N} FS RESPDOR was used to assign multicomponent active pharmaceutical ingredients (APIs) as salts or cocrystals. FS HMQC also provided enhanced sensitivity for ¹H{¹⁷O} and ¹H{³⁵Cl} HMQC experiments on ¹⁷O-labeled Fmoc-alanine and histidine hydrochloride monohydrate, respectively. FS HMQC and FS RESPDOR experiments will provide access to valuable structural constraints from materials that are challenging to study due to unfavorable relaxation times or dilution of the nuclei of interest.     

Loss of methyl radical from some small immonium ions: Unusual violation of the even-electron rule

Several small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R¹, R², R³ = H or alkyl) eliminate ^.CH₃; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even-electron rule, which states that closed-shell cations usually decompose to give closed-shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH₃)₂C?NH]^+.) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH₃^. and CD₃^., via different mechanisms, but very little CH₂D^. or CHD₂^. loss occurs.     

Three new isomers of [C2H6O]+˙: The radical cations [CH3O(H)CH2]+˙, [CH3CHOH2]+˙ and a low-energy isomer of unassigned structure

Three new [C₂H₆O]⁺˙ ions have been generated in the gas phase by appropriate dissociative ionizations and characterized by means of their metastable and collisionally induced fragmentations. The heats of formation, ΔH_f⁰, of the two ions which were assigned the structures [CH₃O(H)CH₂]⁺˙ and [CH₃CHOH₂]⁺˙ could not be measured. The third isomer, to which the structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = \mathop {\rm C}\limits^{\rm .} {\rm H} \cdot \cdot \cdot \mathop {\rm H}\limits^ + \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} is tentatively assigned, was measured to have ΔH_f⁰ = 732±5 kJ mol^?1, making it the [C₂H₆O]⁺˙ isomer of lowest experimental heat of formation. It was found that the exothermic ion–radical recombinations [CH₂OH]⁺+CH₃˙→[CH₃O(H)CH₂]⁺˙ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm + } {\rm HOH + H}^{\rm .} $\end{document}→[CH₃CHOH₂]⁺˙ have large energy barriers, 1.4 and ?0.9 eV, respectively, whereas the recombinations yielding [CH₃CH₂OH]⁺˙ have little or none.