Semiempirical calculations of carbenes with aromatic substituents: a comparison of theory with experiment

Abstract

M+ -4 Cl), 440 (M+ -6 Cl), 403 (M+ -C6C18). (b) A complex mixture (0.045 g) containing some fluorenyl radical 15 (IR spectrum).Perchloro-4-(phenyl(4-pyridyl)methylene)cycIohexa-2,5dienone (17). A mixture of radical 13 (0.414 g) and 30% oleum (20 mL) was stirred (23 h) at room temperature and in the dark. The resulting mixture was poured into ice-water and extracted with ether-CHCl3. The resulting solution was dried and evaporated to a residue, which by chromatography through silica gel (CC14) yielded starting radical 13 (0.160 g; 39%) and dienone 17 (0.221 g; 55%): orange crystals, mp 288-290 °C; IR (KBr) 1652 (s), 1551 (m), 1508 (s), 1470 (m), 1350 (m), 1330 (s), 1305 (s), 1252 (m), 1218 (m), 1195 (m), 1127 (s), 1008 (s), 852 (m), 765 (m), 750 (s), 730 (s), 718 (m), 670 (s), 647 (m), 628 (m), 521 (m), 502 (m) cm"1; UV-vis (CHC13), Table I of supplementary material. Anal.

Singlet and triplet states in the reactions of nitrenium ions

“…In contrast, the singlet possesses a planar structure and a shortened C-N bond (1.311 Å ) consistent with its cyclohexadienyl imine cation character. This finding holds true at all levels of theory starting with AM1 semiempirical calculations 11,[37][38][39] all the way up to DFT calculations (BVWN5/cc-pVTZ//BVWN5/ccpVDZ). 40 Apparently the triplet behaves as a protonated triplet nitrene.…”

Correlation of singlet‐triplet gaps for aryl carbenes calculated by MINDO/3, MNDO, AM1, and PM3 with Hammett‐type substituent constants

“…22 Recently, Schuster and Li applied these semiempirical methods to a systematic study of a wide variety of arlycarbenes. 16 Their work shows that MINDO/3, MNDO, and AM1 calculations give values of singlet-triplet gaps that are approximately linearly related to the experimental estimates of the energy gap. On the other hand, to our knowledge, there are no reports in the literature on the relationships between substituent constants (Hammett type) and calculated properties of arylcarbenes by MINDO/3, MNDO, AM1, and PM3 semiempirical molecular orbital methods.…”

SOMO–HOMO Conversion in Triplet Carbenes

“…The energetic preference of the triplet state of CH 2 over the closed-shell/open-shell singlets was computed to be 2.6/1.1 kcal mol −1 . 34 In the case of DBC, the energetic preference of the triplet state over the closed-shell singlet was computed to be 11.4 kcal mol −1 . The singlet ground state was computed for O and NH with the singlet preference of 6.8 and 8.6 kcal mol −1 , respectively, at the same of level of theory.…”

“…The singlet ground state was computed for O and NH with the singlet preference of 6.8 and 8.6 kcal mol −1 , respectively, at the same of level of theory. 34 In summary, the SOMO−HOMO energy conversion phenomenon was examined for the first time in triplet diarylcarbenes. Triplet carbenes 4−8C C1 and 4−11C C2v with the curved π-conjugated cycloparaphenylene structure and planar carbenes F, CH 2 , O, and NH possessed the SOMO− HOMO converted electronic configuration as their most stable electronic configuration.…”

“…To understand the generality of the SOMO–HOMO conversion phenomenon in triplet carbenes, several diarylcarbenes, CH 2 (X = CH 2 ), O (X = O), and NH (X = NH) in C S symmetry and DBC in C 2 symmetry, in addition to planar carbene F , were computed at the UB3LYP/6-31G­(d) level of theory (Figures b–e). Surprisingly, the SOMO–HOMO conversion was observed in planar triplet carbenes CH 2 , O , and NH featuring the relatively small carbene angles (θ C ), although the HOMO and SOMO–1 are degenerated in CH 2 (Figure b).…”