Isoselenocyanates versus Isothiocyanates and Isocyanates

Conformers of Allyl Isothiocyanate: A Combined Microwave Spectroscopy and Computational Study

The pure rotational spectrum of allyl isothiocyanate (CH₂=CHCH₂-NCS) was collected from 4 to 26 GHz using Fourier transform microwave (FTMW) spectroscopy. Its analysis revealed the presence of two conformers that arise due to variation in the CCCN and CCNC dihedral angles. The observed spectrum is consistent with the accompanying potential energy surfaces derived using quantum chemical calculations at the B3LYP-D3(BJ) and MP2 levels of theory. Together, this experimental and theoretical study unequivocally identifies a new conformer (I) as the global minimum geometry. The spectral assignment of this new conformer is verified by the observation of transitions consistent with its ³⁴S, ¹³C, and ¹⁵N isotopologues and with the characteristic ¹⁴N quadrupole hyperfine patterns. For conformer I, the substitution (r_s) and effective ground state (r₀) structures were derived and reveal contributions from a large amplitude motion in the CCNC angle. The remaining geometric parameters compare well with the equilibrium structure (r_e) from B3LYP-D3(BJ)/cc-pVQZ calculations. The derived CNC bond angle of 152.6(3)° for conformer I of allyl-NCS is found to be ∼15° larger than that of allyl-NCO (137.5(4)°), which is in line with a change in the hybridization at nitrogen from an orbital with more ∼sp character in allyl-NCS to ∼sp^1.5 in allyl-NCO as determined via natural bond orbital analyses.

Rotational Spectra and Structures of Phenyl Isocyanate and Phenyl Isothiocyanate

The pure rotational spectra of phenyl isocyanate (PhNCO) and phenyl isothiocyanate (PhNCS) were investigated using Fourier transform microwave spectroscopy in the range from 4 to 26 GHz. For each molecule, rotational transitions due to the parent species and nine minor isotopologues including seven ¹³C, one ¹⁵N, and one ¹⁸O/³⁴S have been observed in natural abundance. The r_m⁽¹⁾ geometries were derived from the resulting sets of rotational constants and are consistent with the equilibrium structures (r_e) from ab initio calculations performed at the MP2/aug-cc-pVTZ level. NBO and Townes-Dailey analyses were conducted to better understand the electronic structure and geometry of each compound. In the case of PhNCS, the nitrogen atom displays more sp-like character resulting in shorter C-N bonds and a larger CNC angle relative to those of PhNCO.

Polyselenoureas via Multicomponent Polymerizations Using Elemental Selenium as Monomer

Multicomponent polymerizations (MCPs) have emerged as a powerful tool in the synthesis of advanced, sequence-regulated polymers based on their mild reaction conditions, ease of use, and high atom economy. Herein, we exploit MCP methodology to introduce elemental selenium into a polymer chain, accessing a unique polymer class,i.e., polyselenoureas. These polyselenoureas can be synthesized from a broad range of commercially available starting materials, in a simple ambient temperature one-step procedure. The incorporation of selenium directly into the polymer backbone provides a unique handle for polymer characterization based on the distinctive isotope profiles exposed by high-resolution mass spectrometry, along with diagnostic signals observed in infrared and X-ray photoelectron spectroscopies. In addition, diffusion ordered spectroscopy provides access to hydrodynamic diameter information on the generated unique polymer class.