New Carbenes and Cyclic Allenes Energetically Comparable to Experimentally Known 1-Azulenylcarbene

Abstract

1-Azulenylcarbene ( 18 ; 0 kJ mol –1 ) is experimentally known as the key reactive intermediate for the rearrangement reactions of aryl carbenes in the laboratory. Here, using coupled-cluster methods up to the fc-CCSD(T)/cc-pVTZ//fc-CCSD(T)/cc-pVDZ level, thirteen new carbenes and one new cyclic allene are theoretically identified within the C 11 H 8 elemental composition that either energetically lie below or very close to 18 . While the cyclic allene, bicyclo[5.4.0]undeca-2,3,5,7,9,11-hexene ( 1 ; −166 kJ mol –1 ), is the experimentally known lowest energy isomer, three other cyclic allenes, bicyclo[5.4.0]undeca-1,2,4,6,8,10-hexene ( 2 ; −100 kJ mol –1 ), bicyclo[5.4.0]undeca-1,3,4,6,8,10-hexene ( 3 ; −97 kJ mol –1 ), and bicyclo[6.3.0]undeca-1,2,4,6,8,10-hexene ( 13 ; −42 kJ mol –1 ), demand new experimental studies. In total, thirty-one isomers are studied in this work (within −166 to +15 kJ mol –1 from 18 ) and all are found to be polar (μ ≠ 0). Among these, 1H-benzo[7]annulen-1-ylidene ( 17 ; −4 kJ mol –1 ; μ = 5.24 D), bicyclo[5.4.0]undeca-2,4,6,8,11-pentaene-10-ylidene ( 24 ; 13 kJ mol –1 ; μ = 7.59 D), 5-methylene-naphthalen-1-ylidene ( 26 ; 15 kJ mol –1 ; μ = 5.32 D), 6-methylene-naphthalen-2-ylidene ( 27 ; −43 kJ mol –1 ; μ = 6.60 D), and 8-methylene-naphthalen-2-ylidene ( 28 ; −39 kJ mol –1 ; μ = 5.55 D) are competitively polar compared to 18 (μ = 5.39 D). Therefore, these carbene molecules are potential targets for rotational spectroscopists and radioastronomers. Considering the importance of naphthyl and azulenylcarbenes in reactive intermediate chemistry, mechanisms of different rearrangement reactions and plausible formation pathways of some of these new carbenes are studied in this work using density functional theory.

Energetic and Spectroscopic Properties of the Low-Lying Isomers of C5H: A High-Level Ab Initio Study

“…The canonical forms of isomer 1 are shown in Figure 2. The electronic structures of the rest of the isomers (6)(7)(8)(9)(10)(11)(12)(13)(14) are listed in Figure 3. After several attempts, structures of the isomers 13, 14, 3-c, and 4-a could not be optimized at the coupled-cluster level.…”

“…The time evolution of the total energy of the first five minimum energy isomers (1-5) at the given condition is described in Figure 7. AIMD results for other isomers (6)(7)(8)(9)(10)(11)(12)(13)(14) are shown in Figure S8 (Supplementary Materials). From Figure 7, it can be clearly predicted that isomers 1, 2, and 3 are kinetically the most stable isomers.…”

“…The following supporting information can be downloaded at: https://www. mdpi.com/article/10.3390/atoms11090115/s1, Figure S1 S1: Optimized geometries of the C 5 H isomers (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) along with their cationic and anionic forms in Cartesian coordinates (in Angstrom units) obtained at UB3LYP/6-311+G (d,p) level of theory; Table S2: Geometries of transition states involved in the rearrangement scheme in Cartesian coordinates (in Angstrom units) obtained at UB3LYP/6-311+G (d,p) level of theory; Table S3: Point group, relative zero-point corrected energy (∆E 0 in kJ mol −1 ), dipole moments (in Debye) and rotational constants (in MHz) of C 5 H isomers of 1-14 in their ground electronic states calculated at the UB3LYP/6-311+G(d,p) level of theory; Table S4: Point group, relative zero-point corrected energy (∆E 0 in kJ mol −1 ), dipole moments (in Debye) and rotational constants (in MHz) of cationic counterpart of C 5 H isomers of 1-14 in their singlet ground electronic states calculated at the UB3LYP/6-311+G(d,p) level of theory. Table S5: Point group, relative zero-point corrected energy (∆E 0 in kJ mol −1 ), dipole moments (in Debye) and rotational constants (in MHz) of anionic counterpart of C 5 H isomers of 1-14 in their singlet ground electronic states calculated at the UB3LYP/6-311+G(d,p) level of theory; Table S6: Point group, relative zero-point corrected energy (∆E 0 in kJ mol −1 ), dipole moments (in Debye) and rotational constants (in MHz) of cationic counterpart of C 5 H isomers of 1-14 in their triplet ground electronic states calculated at the UB3LYP/6-311+G(d,p) level of theory; Table S7: Point group, relative zero-point corrected energy (∆E 0 in kJ mol −1 ), dipole moments (in Debye) and rotational constants (in MHz) of anionic counterpart of C 5 H isomers of 1-14 in their triplet ground electronic states calculated at the UB3LYP/6-311+G(d,p) level of theory; Table S8: Point goup, relative zero-point corrected energy (∆E 0 in kJ mol −1 ), dipole moments (in Debye) and rotational constants (in MHz) of C 5 H isomers of 1-14 in their ground electronic states calculated at the UωB97XD/6-311+G(d,p) level of theory; Table S9: Point group, relative zero-point corrected energy (∆E 0 in kJ mol-1), dipole moments (in Debye) and rotational constants (in MHz) of cationic counterpart of C 5 H isomers of 1-14 in their singlet ground electro...…”

“…Out of all the molecules detected, approximately one-fourth of them are hydrocarbons, mostly unsaturated in nature, with a low H/C ratio [8]. These unsaturated hydrocarbons have not only played crucial roles in the chemical evolution of molecular gas clouds but also helped in the combustion processes and formation of polycyclic aromatic hydrocarbons (PAHs) through various resonantly stabilized free radicals (RSFRs) [9] and carbenes [10][11][12]. Many RSFRs have been identified as responsible carriers of unidentified diffuse interstellar bands (DIBs) [13].…”

Energetic and Spectroscopic Properties of Astrophysically Relevant MgC4H Radicals Using High-Level Ab Initio Calculations

“…However, the synthesis, characterization, and eventual identification of such transient species in the laboratory are not a very easy task. Therefore, computational studies on the structure and electronic properties of these astrophysically important molecules may aid the radioastronomers, molecular spectroscopists, and synthetic organic chemists to identify them both in the laboratory as well as in the ISM. ,− Moreover, the spectroscopic detection and identification of these molecules can be challenging due to the presence of the metal atom having many closely spaced electronic states with different spin multiplicities.…”