Radical reaction C3H+NO: a mechanistic study

The Simplest, Isolable, Alkynyl Isocyanate HC≡CNCO: Synthesis and Characterization

Alkynyl isocyanates have been postulated as highly reactive intermediates in synthetic chemistry. Herein, the parent molecule HC≡CNCO is isolated for the first time. In sharp contrast to the previously reported short lifetime (ca. 15 s) at room temperature, we found that HC≡CNCO has a lifetime of 55 h in the gas phase (2 mbar, 300 K) with a melting point of -79.5 °C and vaporization enthalpy (ΔH_vap ) of 23.1(1) kJ mol^-1 . Apart from the IR (gas, solid, and matrix), ¹ H and ¹³ C NMR, and UV/Vis spectroscopic characterization, its photoisomerization with a acylnitrene HC≡CC(O)N and cyanoketene NCC(H)CO has been observed.

Rate constants for the N(2D) + C2H2 reaction over the 50–296 K temperature range

The reactions of metastable atomic nitrogen N(²D) are important processes in the gas-phase chemistry of several planetary atmospheres.

Symmetry breaking and spectral considerations of the surprisingly floppy c-C3H radical and the related dipole-bound excited state of c-C3H. J Chem Phys 2017;146:224303. [PMID: 29166048 DOI: 10.1063/1.4985095]

The C₃H radical is believed to be prevalent throughout the interstellar medium and may be involved in the formation of polycyclic aromatic hydrocarbons. C₃H exists as both a linear and a cyclic isomer. The C_2v cyclopropenylidenyl radical isomer was detected in the dark molecular cloud TMC-1, and the linear propenylidenyl radical isomer has been observed in various dark molecular clouds. Even though the c-C₃H radical has been classified rotationally, the vibrational frequencies of this seemingly important interstellar molecule have never been directly observed. Established, highly accurate quartic force field methodologies are employed here to compute useful geometrical data, spectroscopic constants, and vibrational frequencies. The computed rotational constants are consistent with the experimental results. Consequently, the three a₁ (ν₁, ν₂, and ν₃) and one b₁ (ν₆) anharmonic vibrational frequencies at 3117.7 cm^-1, 1564.3 cm^-1, 1198.5 cm^-1, and 826.7 cm^-1, respectively, are reliable predictions for these, as of yet unseen, observables. Unfortunately, the two b₂ fundamentals (ν₄ and ν₅) cannot be treated adequately in the current approach due to a flat and possible double-well potential described in detail herein. The dipole-bound excited state of the anion suffers from the same issues and may not even be bound. However, the trusted fundamental vibrational frequencies described for the neutral radical should not be affected by this deformity and are the first robustly produced for c-C₃H. The insights gained here will also be applicable to other structures containing three-membered bare and exposed carbon rings that are surprisingly floppy in nature.