Meldrum's acid derivatives and isoxazolopyrimidinone precursors for generation of iminopropadienones R–N=C=C=C=O 1 by FVT.
Three Meldrum's acid-based precursors of MeNCCCO 1a.
The pyridopyrimidinone precursor 5 yielding MeNCCCO 1a and 2-PyNCCCO 7.
Generation of bis(phenylimino)propadiene, Ph-N=C=C=C=N-Ph 9.
IR spectrum of MeN=C=C=C=O 1a formed by FVT of 5-[(dimethylamino)(methylamino)methylene]-Meldrum's acid 4a at 800 °C and isolated in Ar matrix at 14 K. W: water; C: carbon dioxide (2345 and 2340 cm−1); CO: carbon monoxide (2138 cm−1); A: acetone (1721, 1361, 1216, 1094, and 883 cm−1); D: dimethylamine (3193, 2973, 2838, 2793, 2789, 1482, 1478, and 1457 cm−1); I: ketenimine intermediate I (Scheme 2 ) (2076 cm−1). Bands assigned to MeNC3O 1a: 2279 (vs)(νas NCCCO), 2269, 2243, 2224, 2214 (shoulder), 2184, 2163 (νs NCCCO), 2126, 1611, and 1418 cm−1 together with very weak bands at 1445, 1433, 1137, 1018, and 558 cm−1.
Calculated “linear” and “bent” structures of Me-NCCCO (1a and 1a ′ ) at the LCCSD(T)/cc-pVTZ level (bond lengths in Å; bond angles and dihedral angles τ in degrees (°)). The energy difference between 1a and 1a ′ is ΔE = 0.03 kcal mol−1. The energy barrier for linearization in 1a′ is 3.1 kcal mol-1.
Description of the modes involved in active fundamental overtones and combination bands in the 2100–2300 cm−1 region for 1a.
IR spectra (Ar matrix, 15 K) of (a) PhNCCCO 1b, (b) Ph15NCCCO, and (c) PhNCC13CO in the cumulene region. The compounds were generated by FVT of 2b at 600 °C (cf. Figure S3). Peaks A: 2247; B: 2243; C: 2220; D: 2140; E: 2245; F: 2242; G: ∼2220; H: 2124; I: 13CO2 ; J: 2222; K: 2080 cm−1.
Description of the modes involved in active fundamental overtones and combination bands in the 2100–2300 cm−1 region for 1b.
IR spectra (Ar matrix, 12 K) of PhN=C=C=C=NPh 9 and its isotopomers as generated by FVT of 8 at 800 °C: (a) unlabeled, (b) Ph15NCCCNPh, and (c) PhN13CCCNPh. Peaks A: 2175; B: 2162; C: 2156; D: 2138; E: 2060; F: 2166; G: 2136; H: 2055; I: 2165; J: 2140; K: 2118 cm−1.
Experiental wavenumbers for methyliminopropadienone and calculated anharmonic wavenumbers for 1a (“linear”) and 1a ′ (“bent”). a
Anharmonic wavenumbers ν (cm−1), principal assignments, and dominant contribution (%) for Me-NCCCO 1a in the range 2100–2300 cm−1.
Anharmonic wavenumbers ν (cm−1), principal assignments, and dominant contribution (%) for Ph-NCCCO 1b and its isotopomers in the range 2100–2315 cm−1 (see Table S1 for the full set of data).
Anharmonic wavenumbers ν (cm−1), principal assignments, and dominant contribution (%) for Ph-NCCCN-Ph 9 and its isotopomers in the range 2000–2250 cm−1 (see Table S2 for the full set of data).
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