Infrared Spectra of Cyanoacetaldehyde (NCCH2CHO): A Potential Prebiotic Compound of Astrochemical Interest

Cyanoacetaldehyde (NC? CH₂CH?O) and its isomer, cyanovinylalcohol (NC? CH?CH? OH), as possible components of the interstellar medium, comets, or planetary atmospheres, exist in equilibrium in the gas phase, although the latter compound is very much in the minority (2 %). The recording and analysis of the gas‐phase infrared spectrum of the former compound within the 4000–500 cm^?1 spectroscopic range and the potential presence of the latter isomer, which could be vital for their detection in these media, are reported. CCSD(T) and G4 high‐level ab initio methods, as well as density functional theory calculations, predict the existence of two stable rotamers of cyanoacetaldehyde. The global minimum has a structure with an unusual O‐C‐C‐C dihedral angle (150°) that falls between the antiperiplanar (180°) and anticlinal forms (120°). The second rotamer, which is about 4.0 kJ mol^?1 less stable in terms of free energy, has a planar structure that corresponds to the synperiplanar form (O‐C‐C‐C dihedral angle: 0°). The absorption vibrational bands of the two aldehyde rotamers that are present in the mixture lead to a spectrum with a very complex structure in the region of deformation movements, in which several low‐intensity bands overlap. A complete and unambiguous assignment of the experimental spectrum has been achieved by using the calculated harmonic and anharmonic vibrational frequencies.     

On the Structures,Lifetimes, and Infrared Spectra of Alkylmercury Hydrides

A series of six small alkylmercury hydrides of the general formula RHgH with R=methyl, ethyl, n‐propyl, isopropyl, n‐butyl, and 3‐butenyl were obtained by reduction in vacuo of the corresponding mercury halide with tributyltin hydride in the presence of a radical inhibitor. These very reactive compounds, which have to be removed from the reaction mixture as they are formed, were characterized by ¹H NMR and ¹³C NMR spectroscopy. The IR spectra of n‐propyl‐, isopropyl‐, n‐butyl‐, and 3‐butenylmercury hydride were recorded for the first time. All compounds were then studied by density functional theory calculations on the basis of a recent theoretical assessment for alkylmercury compounds performed by our group. Comparison of the experimental and theoretical results allowed the assignment of the vibrational modes in an unambiguous way, in spite of the low intrinsic stability of some of the derivatives investigated. The experimental procedure implemented for registering the IR spectra of these unstable species in the gas phase allowed us to obtain reasonable estimates of their lifetimes.     

α,β‐Unsaturated and Saturated Derivatives of Be,Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

The gas-phase acidity of R--XH (R=H, CH(3), CH(2)CH(3), CH==CH(2), C[triple chemical bond]CH; X=Be, Mg, Ca) alkaline-earth-metal derivatives has been investigated through the use of high-level CCSD(T) calculations by using a 6-311+G(3df,2p) basis set. BeH(2) is a stronger acid than BH(3) and CH(4) for two concomitant reasons: 1) the dissociation energy of the Be--H bond is smaller than the dissociation energies of the B--H and C--H bonds, and 2) the electron affinity of BeH(.) is larger in absolute value than those of BH(2) (.) and CH(3) (.). The acidity also increases on going from BeH(2) to MgH(2) due to these two same factors. Quite importantly, despite the fact that the X--H bonds in the R--XH (X=Mg, Ca) derivatives exhibit the expected X(delta+)--H(delta-) polarity, they behave as metal acids in the gas phase and only Be derivatives behave as carbon acids in the gas phase. The ethylberyllium hydride exhibits an unexpected high acidity compared with the methyl derivative because deprotonation of the system is accompanied by a cyclization that stabilizes the anion. Similarly to that found for derivatives that contain heteroatoms from groups 14, 15, and 16, the unsaturated compounds are stronger acids than the saturated counterparts, with the only exception of the Ca-vinyl derivative. Most importantly, among ethyl, vinyl, and ethynyl derivatives containing a heteroatom of the main group of the Periodic Table, those containing Be, Mg, and Ca are among the strongest gas-phase acids.     

New di-(beta-chloroethyl)-alpha-amides on N-(meta-acylamino-benzoyl)- D,L-aminoacid supports with antitumoral activity

In order to obtain new compounds with antitumoural action the N-(meta-acylaminobenzoyl)-alpha-acylaminobenzoyl)-alpha-aminoacids 4-9 were prepared. These compounds were subsequently converted into the corresponding Delta(2)-oxazolin-5-ones 10-15, which in turn were submitted to a ring opening reaction with di-(beta-chloroethyl)amine to afford the peptide supported N-mustards 16-21, which showed low toxicity and cytostatic activity similar to that of sarcolisine against the Ehrlich ascite and Walker 253 carcinosarcoma.     

Why Are Selenouracils as Basic as but Stronger Acids than Uracil in the Gas Phase?

The gas‐phase basicity and acidity of 2‐selenouracil ( 2SU ), 4‐selenouracil ( 4SU ), and 2,4‐diselenouracil ( 24SU ) have been calculated at the B3LYP/6‐311+G(3df,2p) level of theory. Our results showed that all these compounds behave as bases of moderate strength in the gas phase. As was found for uracil and for the thiouracil analogues, the most basic site is the heteroatom at position 4, and only for 2SU is there a certain ambiguity in assigning the basic site. More importantly, with the only exception of 2SU , selenouracils are as basic as or slightly less basic than uracil, because the replacement of the oxygen atom at position 2 by a selenium atom leads to an increase of the electron delocalization inside the six‐membered ring, which decreases the intrinsic basicity of the heteroatom at position 4. As already reported for uracil and thiouracils, for selenouracils N1 is the most acidic site. However, selenouracils are predicted to be stronger acids than uracil. This acidity enhancement is essentially due to a specific stabilization of the anion when O is replaced by Se. Two factors are responsible for this stabilization: a significant aromatization of the ring upon deprotonation and a better dispersion of the excess electron density when the system contains third‐row atoms.     

Ni+ reactions with aminoacrylonitrile, a species of potential astrochemical relevance

The reaction of aminoacrylonitrile, a species of astrochemical interest, with Ni(+)((2)D(5/2)) was investigated by means of mass spectrometry techniques and density functional theory calculations. The dominant fragmentations in the MIKE spectrum correspond to the loss of [C2,N,H3], HCN, and NH3, the loss of H2 being very minor. The structure and bonding of the different aminoacrylonitrile-Ni(+) complexes were investigated at the B3LYP/6-311G(d,p) level of theory. The same approach was employed in our survey of the corresponding potential energy surface. This survey indicates that the [C2,N,H3] neutral product can be formed either as ketenimine (CH2CNH) or acetonitrile. The formation of the latter is significantly more exothermic but involves slightly higher activation barriers; so very likely, both isomers are produced along the reaction process. The lost of HNC is not competitive with the loss of HCN, because when the former is formed the products lie higher in energy and the corresponding mechanisms involve energy barriers above the entrance channel. The loss of NH3 is associated with the formation of a complex between cyanoacetylene, HCCCN, which is very abundant in the interstellar media, and Ni(+).     

Gas-phase protonation and deprotonation of acrylonitrile derivatives N[triple chemical bond]C--CH==CH--X (X=CH(3), NH(2), PH(2), SiH(3))

A combined experimental and theoretical study on the gas-phase basicity and acidity of a series of cyanovinyl derivatives is presented. The gas-phase basicities and acidities of (N[triple chemical bond]C--CH==CH--X, X=CH(3), NH(2)) were obtained by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry techniques. The corresponding calculated values were obtained at the G3B3 level of theory. The effects of exchanging CH(3) for SiH(3), and NH(2) for PH(2), were analyzed at the same level of theory. For the neutral molecules, the Z isomer is always the dominant species under standard gas-phase conditions at 298 K. The loss of the proton from the substituent X was found systematically to be much more favorable than deprotonation of the HC==CH linking group. The corresponding isomeric E ion is much more stable than the Z ion, so that only the former should be found in the gas phase. The most significant structural changes upon deprotonation occur for the methyl and amino derivatives because, in both cases, deprotonation of X leads to a significant charge delocalization in the corresponding anion. Protonation takes place systematically at the cyano group, whereby the isomeric E ion is again more stable than the Z ion. Push-pull effects explain the preference of aminoacrylonitrile to be protonated at the cyano group, which also explains the high basicity of this derivative relative to other members of the analyzed series that present rather similar gas-phase basicities, GB approximately 780 kJ mol(-1), indicating that the different nature of the substituents has only a weak effect on the intrinsic basicity of the cyano group. The cyanovinyl derivatives have a significantly stronger gas-phase acidity than that of the corresponding vinyl compounds CH(2)==CH--X. This acidity-strengthening effect of the cyano group is attributed to the greater stabilization of the anion with respect to the corresponding neutral compound.