The structure and CC vibrational frequencies of the all-trans polyenes C2nH2n+2(n = 2 − 15), C2nH2n(Me)2(n = 2 - 13), and C2nH2n(tert-Butyl)2(n = 2 - 5): Computational results

Carbon-carbon bond lengths and CC vibrational frequencies are reported for the linear, all-trans unsubstituted C2nH2n+2 (n = 2 - 15), methyl capped C2nH2nMe2 (n = 2 - 13), and tert-butyl capped C2nH2n(tert-butyl)2 (n = 2 -5 ) polyenes (C2h) calculated at the B3LYP/6-311++G(d,p) level. The CC/CC 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 CC/CC bonds is ∼0.06 Å for C30H32 and C26H26Me2. The Ag, in-phase, harmonic CC 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 CC frequency for the methyl capped polyenes decreases from 1717.9 cm−1 (n = 2) to 1539.6 cm−1 (n = 13), and the anharmonic CC frequency decreases from 1675.0 cm−1 (n = 2) to 1562.8 cm−1 (n = 7).

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