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The structure and C[dbnd]C vibrational frequencies of the all-trans polyenes C2 nH2 n +2(n = 2 − 15), C2 nH2 n(Me)2(n = 2 – 13), and C2 nH2 n(tert-Butyl)2(n = 2 – 5): Computational results

par De Mare, George ;Rao, Niny N.Z.;Bock, Charles C.W.
Référence Chemical Data Collections, 11-12, page (25-35)
Publication Publié, 2017-12

Article révisé par les pairs

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Résumé :

Carbon-carbon bond lengths and C[dbnd]C vibrational frequencies are reported for the linear, all-trans unsubstituted C2nH2 n +2 (n = 2 – 15), methyl capped C2 nH2 nMe2 (n = 2 – 13), and tert-butyl capped C2 nH2 n(tert-butyl)2 (n = 2 –5) polyenes (C2h) calculated at the B3LYP/6-311++G(d,p) level. The C[dbnd]C/C–C bond length alternation remains evident at this level for the unsubstituted and methyl capped polyenes as the chain length increases; the center-most difference in the length of the C–C/C[dbnd]C bonds is ∼0.06 Å for C30H32 and C26H26Me2. The Ag, in-phase, harmonic C[dbnd]C Raman frequency for the unsubstituted polyenes decreases from 1699.2 cm−1 (n = 2) to 1528.9 cm−1 (n = 15); the anharmonic frequency decreases from 1651.5 cm−1 (n = 2) to 1547.7 cm−1 (n = 8). The harmonic C[dbnd]C frequency for the methyl capped polyenes decreases from 1717.9 cm−1 (n = 2) to 1539.6 cm−1 (n = 13), and the anharmonic C[dbnd]C frequency decreases from 1675.0 cm−1 (n = 2) to 1562.8 cm−1 (n = 7).