Theoretical studies of two key low-lying carbenes of C5H2 missing in the laboratory

• Verfasst von: Thimmakondu, Venkatesan S. [VerfasserIn]
• Verfasst von: Ulusoy, Inga [VerfasserIn]
• Titel: Theoretical studies of two key low-lying carbenes of C5H2 missing in the laboratory
• Verf.angabe: Venkatesan S. Thimmakondu, Inga Ulusoy, Angela K. Wilson, and Amir Karton
• E-Jahr: 2019
• Jahr: July 3, 2019
• Umfang: 10 S.
• Fussnoten: Im Titel sind die Zahlen "5" und "2" tiefgestellt ; Gesehen am 26.11.2019
• Titel Quelle: Enthalten in: The journal of physical chemistry <Washington, DC> / A
• Ort Quelle: Washington, DC : Soc., 1997
• Jahr Quelle: 2019
• Band/Heft Quelle: 123(2019), 30, Seite 6618-6627
• ISSN Quelle: 1520-5215
• DOI: doi:10.1021/acs.jpca.9b06036
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1683506278

Abstract

The equilibrium geometries and spectroscopic properties of two key singlet carbenes, buta-1,3-diynylcarbene (6) and 2-methylenebicyclo[1.1.0]but-1(3)-en-4-ylidene (9), which have not been experimentally observed to date, are investigated using high-level coupled-cluster (CC) methods. The current theoretical study necessitates new experimental data on C5H2 isomers considering the relevance of these molecules to interstellar chemistry. Bent-pentadiynylidene (4) has been missing in the laboratory and the prime focus of our earlier theoretical work. The present theoretical study indicates that isomers 6 and 9 are also viable experimental targets. Apart from ethynylcyclopropenylidene (2), pentatetraenylidene (3), ethynylpropadienylidene (5), and 3-(didehydrovinylidene)cyclopropene (8), which are identified by Fourier transform microwave spectroscopy, the dipole moments of elusive 4, 6, and 9 are also nonzero (μ ≠ 0). The relative energies of these isomers, calculated at the CCSDT(Q)/CBS level of theory, with respect to linear triplet pentadiynylidene (1) reveal that they all lie within 25.1 kcal mol-1. Therefore, geometric, energetic, aromatic, and spectroscopic parameters are reported here, which may assist the efforts of molecular spectroscopists in the future. Anharmonic vibrational calculations on isomers 6 and 9 indicate that the former is loosely bound and would be challenging to be detected experimentally. Among the undetected carbenes, 9 may be considered as a potential target molecule considering its higher polarity and aromatic nature.