Proton transfer reactions of hydrazine-boranes

International audienceHydrazine-borane and hydrazine-diborane contain respectively 15.4 and 16.9 wt% of hydrogen and are potential materials for hydrogen storage. In this work we present the gas-phase complexation energies, acidities and basicities of hydrazine-borane and hydrazine-bisborane calculated at MP2/6-311+G(d,p) level. We also report the release of dihydrogen from both protonated complexes (Ghydrazine-borane = –20.9 kcal/mol and Ghydrazine-bisborane = –27.2 kcal/mol) which is much more exergonic than from analogues amine-boranes. The addition of the first BH3 to the hydrazine releases 17.1 kcal/mol and the second addition releases 15.8 kcal/mol. The attachment of BH3 also increases the N-H acidity of hydrazine by 46.3 kcal/mol. It was found that the B-H deprotonation leads to intramolecular rearrangement. The basicity values for hydrazine-borane and –bisborane are 180 and 172.8 kcal/mol respectively. For both complexes the protonation centres are located at the boron moiety. The protonated structure of hydrazine-bisborane is cyclic and can be described as H2 captured between a negatively charged B-H hydrogen and positive boron (B-H••H2••B). Atoms in Molecules analysis is used to investigate bond paths in concerning structures

Structure, spectroscopy, and thermal decomposition of 5-chloro-1,2,3,4-thiatriazole: a He I photoelectron, infrared, and quantum chemical study

International audience5-Chloro-1,2,3,4-thiatriazole has been investigated in the gas phase for the first time by mid-infrared and He I photoelectron spectroscopy. The ground-state geometry has been obtained from quantum chemical calculations at the CCSD(T) and B3LYP levels using aug-cc-pVTZ basis set. Ionization potentials have been determined and the electronic structure has been discussed within the frame of molecular orbital theory. IR and photoelectron spectroscopies, supported by quantum chemical calculations at the B3LYP and SAC-CI levels, provide a detailed investigation into the vibrational and electronic character of the molecule. Thermal stability of 5-chloro-1,2,3,4-thiatriazole has been studied both experimentally and theoretically. Flash vacuum thermolysis of the molecule produces fast quantitatively N2, ClCN, and sulfur. Theoretical calculations at the CCSD(T)//B3LYP level predict competitive decomposition routes, starting either with a retro-cycloaddition reaction leading to N2S and ClCN or with a ring opening to chlorothiocarbonyl azide intermediate, to produce finally N2, S, and ClCN. Calculations also predict that N2S is reactive and decomposes in bimolecular reactions to N2 and S

Ionization, intrinsic basicity, and intrinsic acidity of unsaturated diols of astrochemical interest: 1,1- and 1,2-ethenediol: A theoretical survey

The structure, stability, and bonding characteristics of 1,1- and 1,2-ethenediol, their radical cations, and their protonated and deprotonated species were investigated using high-level ab initio G4 calculations. The electron density of all the neutral and charged systems investigated was analyzed using the QTAIM, ELF, and NBO approaches. The vertical ionization potential (IP) of the five stable tautomers of 1,2-ethenediol and the two stable tautomers of 1,1-ethenediol go from 11.81 to 12.27 eV, whereas the adiabatic ones go from 11.00 to 11.72 eV. The adiabatic ionization leads to a significant charge delocalization along the O-C-C-O skeleton. The most stable protonated form of (Z)-1,2-ethenediol can be reached by the protonation of both the anti-anti and the syn-anti conformers, whereas the most stable deprotonated form arises only from the syn-anti one. Both charged species are extra-stabilized by the formation of an O-H O intramolecular hydrogen bond (IHB) which is not found in the neutral system. (Z)-1,2-ethenediol is predicted to be less stable, less basic, and more acidic than its cis-glycolaldehyde isomer. The most stable protonated species of (E)-1,2-ethenediol comes from its syn-syn conformer, although the anti-anti conformer is the most basic one. Contrarily, the three conformers yield a common deprotonated species, so their acidity follows exactly their relative stability. Again, the (E)-1,2-ethenediol is predicted to be less stable, less basic, and more acidic than its trans-glycolaldehyde isomer. Neither the neutral nor the protonated or the deprotonated forms of 1,1-ethenediol show the formation of any O-H O IHB. The most stable protonated species is formed by the protonation of any of the two tautomers, but the most stable deprotonated form arises exclusively from the syn-anti neutral conformer. The conformers of 1,1-ethenediol are much less stable and significantly less basic than their isomer, acetic acid, and only slightly more acidicThis work was carried out with financial support from the projects PID2021-125207NB-C31 and PID2019-110091GB-I00 of the Ministerio de Ciencia, Innovacion y Universidades of Spain (MICINN) and the project Y2020/EMT-6290 (PRIES-CM) of the Comunidad de Madri

New vibrational assignments for the nu1 to nu17 vibrational modes of aziridine and first analysis of the high resolution infrared spectrum of aziridine between 720 cm-1 and 1050 cm-1

International audienceFourier transform spectra of aziridine (C2H4NH) were recorded at high resolution (0.002 or 0.003 cm-1) in the 600-1750 and 1750-4000 cm-1 regions, using a Bruker IFS125HR spectrometer, located at the LISA facility in Creteil. In parallel, the harmonic force field of aziridine was evaluated analytically at the optimized geometry with second-order Møller-Plesset perturbation theory (MP2) together with the correlation-consistent polarized valence triple zeta basis sets cc-pVTZ. These ab initio predictions were used to perform consistent vibrational assignments for the nu1 to nu17 fundamental bands of aziridine observed in the infrared spectra recorded during this study. Finally, a first detailed rotational assignment was performed for two B-type bands located at 772.3571 cm-1 (nu10, CH2 rock) and 997.1592 cm-1 (nu8, NH bend) and for an A-type band located at 904.0429 cm-1 nu17 , ring deform). We noticed that the nu10 band is weakly perturbed, presumably because the v10 = 1 rotational levels are coupled with those of the v18 = 1 dark band located around 817 cm-1 through B-type and C-type Coriolis resonances

Rotational spectroscopy of mono-deuterated oxirane (cc-C2_2H3_3DO) and its detection towards IRAS 16293−-2422 B

We prepared a sample of mono-deuterated oxirane and studied its rotational spectrum in the laboratory between 490 GHz and 1060 GHz in order to improve its spectroscopic parameters and consequently the calculated rest frequencies of its rotational transitions. The updated rest frequencies were employed to detect $c$-C$_2$H$_3$DO for the first time in the interstellar medium in the Atacama Large Millimetre/submillimetre Array (ALMA) Protostellar Interferometric Line Survey (PILS) of the Class 0 protostellar system IRAS 16293$-$2422. Fits of the detected lines using the rotation diagrams yield a temperature of $T_{\rm rot} = 103 \pm 19$ K, which in turn agrees well with 125 K derived for the $c$-C$_2$H$_4$O main isotopologue previously. The $c$-C$_2$H$_3$DO to $c$-C$_2$H$_4$O ratio is found to be $\sim$0.15 corresponding to a D-to-H ratio of $\sim$0.036 per H atom which is slightly higher than the D-to-H ratio of species such as methanol, formaldehyde, ketene and but lower than those of the larger complex organic species such as ethanol, methylformate and glycolaldehyde. This may reflect that oxirane is formed fairly early in the evolution of the prestellar cores. The identification of doubly deuterated oxirane isotopomers in the PILS data may be possible judged by the amount of mono-deuterated oxirane and the observed trend that multiply deuterated isotopologues have higher deuteration rates than their mono-deuterated variants.Comment: 10 pages total; Mon. Not. R. Astron. Soc., accepte

Generation and structural characterization of aluminum cyanoacetylide

Producción CientíficaCombined spectroscopy measurements and theoretical calculations bring to light a first investigation of a metallic cyanoacetylide, AlC3N, using laser ablation molecular beam Fourier transform microwave spectroscopy. This molecule was synthesized in a supersonic expansion by the reaction of aluminum vapour with C3N, produced from solid aluminum rods and BrCCCN in a newly constructed ablation-heating nozzle device. A set of accurate rotational and 27Al and 14N nuclear quadrupole coupling constants have been determined from the analysis of the rotational spectrum and compared with those predicted in a high-level ab initio study, conducting to the assignment of the observed species to linear AlCCCN. We have searched for this species towards the carbon-rich evolved star IRC + 10216 but only an upper limit to its abundance has been obtained.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

Hydrogenation of solid hydrogen cyanide HCN and methanimine CH2NH at low temperature

International audienceContext. Hydrogenation reactions dominate grain surface chemistry in dense molecular clouds and lead to the formation of complex saturated molecules in the interstellar medium. Aims. We investigate in the laboratory the hydrogenation reaction network of hydrogen cyanide HCN. Methods. Pure hydrogen cyanide HCN and methanimine CH2NH ices are bombarded at room temperature by H-atoms in an ultra-high vacuum experiment. Warm H-atoms are generated in an H2 plasma source. The ices are monitored with Fourier-transform infrared spectroscopy in reflection absorption mode. The hydrogenation products are detected in the gas phase by mass spectroscopy during temperature-programmed desorption experiments. Results. HCN hydrogenation leads to the formation of methylamine CH3NH2, and CH2NH hydrogenation leads to the formation of methylamine CH3NH2, suggesting that CH2NH can be a hydrogenation-intermediate species between HCN and CH3NH2. Conclusions. In cold environments the HCN hydrogenation reaction can produce CH3NH2, which is known to be a glycine precursor, and to destroy solid-state HCN, preventing its observation in molecular clouds ices

An experimental study of the reactivity of CN- and C3N- anions with cyanoacetylene (HC3N)

International audienceThe reactions of the CN- and C3N- anions with cyanoacetylene HC3N, of special interest for the chemistry of Titan’s upper atmosphere, have been investigated by means of FTICR mass-spectrometry. Primary ions, CN- and C3N-, have been produced by dissociative electron attachment (DEA) from BrCN and BrC3N, and prepared in a clean way before reaction. Total rate constants have been measured for both reactions at 300 K and are found to be: (3.9 ± 0.5) 10-9 and (1.0 ± 0.2) 10-10 cm3.s-1 for the reaction of HC3N with CN- and C3N-, respectively. For the CN- + HC3N reaction, proton transfer is found to be the only reactive channel within our detection limits. Proton transfer is also dominant for the C3N- + HC3N reaction but the resulting ionic product being identical to the primary ion C3N-, this process is transparent for the kinetics of the C3N- + HC3N reaction and the kinetic rate retrieved corresponds to a slow and competitive detachment pathway. Yet the nature and energetics of the neutral product(s) formed through this process remain unknown. Additional experiments using isotopic products have allowed to retrieve specific rate constants associated to the proton transfer channel in the C315N- + HC3N and C3N- + HC315N reactions and the measured rates are found to be significantly lower than for the CN- + HC3N system. This decrease and the evolution of reactivity when going from CN- to C3N- and the opening of a new detachment pathway is finally discusse

Acidity Enhancement of the Cyclopentadiene Ring by PH2 and AsH2 Substitution

The intrinsic acidity of cyclopentadiene and its PH2 and AsH2 derivatives has been investigated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) level of theory. The calculated intrinsic acidity of cyclopentadiene is consistent with the available experimental data. Substitution of one of the H atoms of the C(sp3)H2 group of cyclopentadiene by PH2 and AsH2 leads to a significant acidity enhancement of 44 and 34 kJ mol-1, respectively. This acidity enhancement is the result of the balance of two opposite effects: a) a decrease in the aromaticity of the anion on going from the unsubstituted to the substituted forms, b) the stabilization of the anion in the substituted derivatives, through an interaction of the π-cloud of the ring with the X–H bonding orbitals of the PH2 or AsH2 groups. This renders the interaction of the substituent with the five membered ring stronger upon deprotonation, as reflected in a strengthening of the C–P and the C–As bonds

Metallic Cyanoacetylides of Copper, Silver and Gold: Generation and Structural Characterization

Producción CientíficaThe metallic cyanoacetylides CuCCCN, AgCCCN, and AuCCCN have been synthesized in the throat of a pulsed supersonic expansion by reaction of metal vapors, produced by laser ablation, and BrCCCN. Their pure rotational spectra in the (X1Σ+) electronic ground state were observed by Fourier transform microwave spectroscopy in the 2-10 GHz frequency region. Importantly, the rotational spectroscopy constants determined from the analysis of the rotational spectra clearly established the existence of metal-CCCN arrangements for all the mentioned cyanoacetylides. A study of the chemical bonding by means of a topological analysis of the electron density helps to understand the preference for metal-C bonding over metal-N bonding.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13