Enantiomere pentatetraene und deren barriere der thermischen razemisierung

Bertsch, Karl; Jochims, Johannes C.

doi:10.1016/s0040-4039(01)83513-9

Cited by 9 publications

(6 citation statements)

References 14 publications

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“…It is interesting to note that the corresponding DE a 0 with triplet spin multiplicity (using the unrestricted B3LYP/6-31G Ã method for the transition state structures) were also closer to the reported experimental data. [9][10] Therefore, this fact is in accordance with Hund's rule which would predict that the triplet transition state structure energy is below the correspond-ing rotated singlet state, as shown below:…”

Section: Computational Detailssupporting

confidence: 82%

“…8 The DH # values between the diastereoisomers is relatively low: 129.64 kJ mol À1 for CH 3 CH --C --C --CHCH 3 and only 112.91 kJ mol À1 for t-Bu(C 6 H 5 )C --C --C --C(C 6 H 5 )t-Bu. 9,10 The values of DG # for the two cases, 132.15 and 125.26 kJ mol À1 , 11 are in agreement with the values for RR 0 C --C --C --CRR 0 (R¼C 6 H 5 , R'¼C(CH 3 ) 2 CH 2 C 6 H 5 ), for example, 125.04 kJ mol À1 . 10 The t-Bu/ C 6 H 5 compound has a remarkably negative activation entropy for isomerization (DS # ¼ À31.99 J mol À1 K À1 ).…”

Section: Introductionsupporting

confidence: 78%

“…9,10 The values of DG # for the two cases, 132.15 and 125.26 kJ mol À1 , 11 are in agreement with the values for RR 0 C --C --C --CRR 0 (R¼C 6 H 5 , R'¼C(CH 3 ) 2 CH 2 C 6 H 5 ), for example, 125.04 kJ mol À1 . 10 The t-Bu/ C 6 H 5 compound has a remarkably negative activation entropy for isomerization (DS # ¼ À31.99 J mol À1 K À1 ). The low barriers are presumably due to zwitterionic or biradical resonance.…”

Section: Introductionsupporting

confidence: 78%

“…The mutual interconversion energy barriers by calculating the B3LYP/6-31G Ã level of theory for compounds 2 and 4 are in good agreement with the previously reported experimental data (for some derivatives of these compounds). 9,10 These results reveal that the mutual interconversion energy barriers for compounds 1-8 decrease on increasing the number of C atoms (chain length) in these compounds (see Table 1).…”

Section: Resultsmentioning

confidence: 82%

“…The energy barrier of the cis-trans isomerization of RR 0 C --C --C --C --C --CRR 0 (R¼C 6 H 5 , R 0 ¼C(CH 3 ) 2 CH 2 C 6 H 5 ) is 79.88 kJ mol À1 . 10 This barrier is too low for the separation of cis and trans isomers, but since the equilibrium constant in such isomers is near unity, 9 it is relatively easy to measure the barrier by coalescence in the NMR spectrum.…”

Section: Introductionmentioning

confidence: 99%

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DFT study and NBO analysis of the mutual interconversion of cumulene compounds

Nori‐Shargh

Deyhimi

Boggs

et al. 2007

J of Physical Organic Chem

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The B3LYP/6-31G Ã method was used to investigate the configurational properties of allene (,9-decanonaene (9). The calculations at the B3LYP/6-31G Ã level of theory showed that the mutual interconversion energy barrier in compounds 1-8 are: 209.73, 131.77, 120.34, 85.00, 80.91, 62.19, 55.56, and 46.83 kJ mol À1 , respectively. The results showed that the difference between the average C --C double bond lengths (d) values in cumulene compounds 1 and 2, is larger than those between 7 and 8, which suggest that with large n (number of carbon atoms in cumulene chain), the d values approach a limiting value. Accordingly, based on the plotted data, the extrapolation to n ¼ 1, gives nearly the same limiting d(i. e., d lim ). Also, NBO results revealed that the sum of p-bond occupancies, p occupancy , decrease from 1 to 8, and inversely, the sum of p-antibonding orbital occupancies, p Ã occupancy , increase from compound 1 to compound 8. The decrease of Dðp occupancy À p Ã occupancy Þ values for compounds 1-8, is found to follow the same trend as the barrier heights of mutual interconversion in compounds 1-8, while the decrease of the barrier height of mutual interconversion in compounds 1-8 is found to follow the opposite trend as the increase in the number of carbon atom. Accordingly, besides the previously reported allylic resonant stabilization effect in the transition state structures, the results reveal that the d values, Dðp occupancy À p Ã occupancy Þ, D(E HOMO À E LUMO ), and the C atom number could be considered as significant criteria for the mutual interconversion in cumulene compounds 1-8. This work reports also useful predictive linear relationships between mutual interconversion energy barriers (DE a 0 ) in cumulene compounds and the following four parameters: d, Dðp occupancy À p Ã

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Section: Computational Detailssupporting

confidence: 82%