A curiously short carbon–carbon double bond?

Synthesis, charge distribution, and dimerization behavior of lithium alkynylselenolates

“…All rings as well as the exocyclic double bond of the molecule lie in one plane. Due to librational effects, the C C bonds in and adjacent to the central ring appear shortened as was discussed by Dunitz earlier [11]. Otherwise, the relevant bond parameters and angles show no peculiarities and are summarized in Table 3.…”

Comment on “Synthesis, Characterization, and Structures of a Persistent Aniline Radical Cation”: A New Interpretation Is Necessary

“…Since the quantum-chemical computations fail to explain the solid-state structural changes convincingly, experimental artifacts might be suspected. [24] In conclusion, the ESR and UV/Vis spectrometric data presented in Ref. [1] do not confirm the green compound as a stoichiometrically pure TBAC + SbF 6 À salt, the quantumchemical data do not convincingly support the reported structural data, and the interpretation of the apparent temperature-dependent structural changes in the solid state is open to interpretations other than the Jahn-Teller effect.…”

Evaluation of 13C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

“…Increased accuracy obtained with X-Ray geometries compared to theoretical ones could be caused by better suitability of the former for describing averaged chemical shifts. For these reasons the calculations described in the present study may not be used as a direct evidence to choose the correct value of C=C bond length in 1 (see [9] - [11]). The question deserves further investigations, particularly in respect of chemical shift averaging and including e®ect of solvent into GIAO calculations.…”

“…GIAO calculations with X-Ray geometry lead to much more accurate 13 C chemical shifts, particularly for C1-C3 atoms. Two available experimental geometries for 1 with C=C bond length set to 1.278 º A (corrected to take into account molecular motion in the crystal) [11] and 1.255 º A (uncorrected) [9] were tested with all the density functionals used (Table 4). Using corrected value an excellent agreement was achieved for C3, while using uncorrected geometry resulted in more accurate prediction of C1 and C2 chemical shifts.…”

“…The compounds 1-3 were selected since both experimental 13 C NMR spectra and X-ray structures are available, thus allowing a detailed comparison and analysis. The X-ray structure of 1 has been recently discussed [9], [10], [11]. In addition, the most di±cult topic for experimental NMR spectroscopy { the correlation of particular geometry parameters with the chemical shifts was investigated.…”