+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Dynamic processes in [16]annulene: Möbius bond-shifting routes to configuration change



Dynamic processes in [16]annulene: Möbius bond-shifting routes to configuration change



Journal of the American Chemical Society 128(51): 16692-16700



Density functional and ab initio methods have been used to study the mechanisms for key dynamic processes of the experimentally known S4-symmetric [16]annulene (1a). Using BH&HLYP/6-311+G** and B3LYP/6-311+G**, we located two viable stepwise pathways with computed energy barriers (Ea = 8-10 kcal/mol) for conformational automerization of 1a, in agreement with experimental data. The transition states connecting these conformational minima have Möbius topology and serve as starting points for non-degenerate pi-bond shifting (configuration change) via Möbius aromatic transition states. The key transition state, TS1-2, that connects the two isomers of [16]annulene (CTCTCTCT, 1 --> CTCTTCTT, 2) has an energy, relative to the S4 isomer, that ranged from 6.9 kcal/mol (B3LYP/6-311+G**) to 16.7 kcal/mol (BH&HLYP/6-311+G**), bracketing the experimental barrier. At our best level of theory, CCSD(T)/cc-pVDZ(est), this barrier is 13.7 kcal/mol. Several other Möbius bond-shifting transition states, as well as Möbius topology conformational minima, were found with BH&HLYP energies within 22 kcal/mol of 1a, indicating that many possibilities exist for facile thermal configuration change in [16]annulene. This bond-shifting mechanism and the corresponding low barriers contrast sharply with those observed for cis/trans isomerization in acyclic polyenes, which occurs via singlet diradical transition states. All Möbius bond-shifting transition states located in [16]- and [12]annulene were found to have RHF --> UHF instabilities with the BH&HLYP method but not with B3LYP. This result appears to be an artifact of the BH&HLYP method. These findings support the idea that facile thermal configuration change in [4n]annulenes can be accounted for by mechanisms involving twist-coupled bond shifting.

Please choose payment method:






(PDF emailed within 0-6 h: $19.90)

Accession: 048840324

Download citation: RISBibTeXText

PMID: 17177419

DOI: 10.1021/ja066152x


Related references

Configuration change in [14]annulene requires möbius antiaromatic bond shifting. Journal of the American Chemical Society 129(2): 274-275, 2007

Hückel and Möbius bond-shifting routes to configuration change in dehydro[4n+2]annulenes. Journal of Organic Chemistry 78(5): 2033-2039, 2013

Möbius aromaticity in [12]annulene: cis-trans isomerization via twist-coupled bond shifting. Journal of the American Chemical Society 127(27): 9704-9705, 2005

14]Annulene: cis/trans isomerization via two-twist and nondegenerate planar bond shifting and Möbius conformational minima. Organic Letters 12(5): 972-975, 2010

Investigation of a putative mobius aromatic hydrocarbon. The effect of benzannelation on mobius [4n]annulene aromaticity. Journal of the American Chemical Society 127(8): 2425-2432, 2005

10]Annulene: bond shifting and conformational mechanisms for automerization. Journal of Organic Chemistry 71(8): 3001-3006, 2006

Tunneling by 16 Carbons: Planar Bond Shifting in [16]Annulene. Journal of the American Chemical Society 141(13): 5286-5293, 2019

Is the [9]annulene cation a Möbius annulene?. Angewandte Chemie 48(52): 9971-9974, 2009

11,11-dimethyl-1,6-methano[10]annulene--an annulene with an ultralong CC bond or a fluxional molecule?. Journal of Physical Chemistry. a 119(9): 1666-1682, 2015

Heterometallic Pd(II)-Ni(II) complexes with meso-substituted dibenzotetraaza[14]annulene: double C-H bond activation and formation of a rectangular tetradibenzotetraaza[14]annulene. Inorganic Chemistry 53(21): 11348-11350, 2014

The [13]annulene cation is a stable Möbius annulene cation. Organic Letters 12(8): 1708-1711, 2010

π-Electron ring-currents and bond-currents in [10,5]-Coronene and related structures conforming to the 'Annulene-Within-an-Annulene' model. Physical Chemistry Chemical Physics 15(21): 8245-8253, 2013

A double-twist Möbius-aromatic conformation of [14]annulene. Organic Letters 7(21): 4637-4639, 2005

Triply twisted Möbius annulene: a new class of two-photon active material--a computational study. Physical Chemistry Chemical Physics 17(10): 6827-6833, 2015

Valence Bond Configuration Interaction: A Practical ab Initio Valence Bond Method That Incorporates Dynamic Correlation. Journal of Physical Chemistry A 106(11): 2721-2726, 2002