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Pregled bibliografske jedinice broj: 406775

The Isomerization Barrier in Cyanocyclobutadienes: An ab Initio Multireference Average Quadratic Coupled Cluster Study


Eckert-Maksić, Mirjana; Lischka, Hans; Maksić, Zvonimir B.; Vazdar, Mario
The Isomerization Barrier in Cyanocyclobutadienes: An ab Initio Multireference Average Quadratic Coupled Cluster Study // Journal of Physical Chemistry A, 113 (2009), 29; 8351-8358 doi:10.1021/jp9015273 (međunarodna recenzija, članak, znanstveni)


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Naslov
The Isomerization Barrier in Cyanocyclobutadienes: An ab Initio Multireference Average Quadratic Coupled Cluster Study

Autori
Eckert-Maksić, Mirjana ; Lischka, Hans ; Maksić, Zvonimir B. ; Vazdar, Mario

Izvornik
Journal of Physical Chemistry A (1089-5639) 113 (2009), 29; 8351-8358

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
ab initio calculations ; antiaromaticity ; isomerism ; strained carbocycles

Sažetak
The energy profiles of the isomerization of mono, di- and tetracyano-substituted cyclobutadienes (CBDs) are computed at the MR- AQCC(4, 4)/CASSCF level of theory. It was found that the energy barrier heights for the automerization reaction are 2.6 (tetracyano- CBD), 5.1 (1, 3-dicyano-CBD) and 6.4 (cyano-CBD) kcal mol-1 implying that they are lowered relative to that in the parent CBD (6.4 kcal mol-1), the monosubstituted derivative being an exception. Since the free CBD shuttles between two equivalent structures even at low temperature of 10 K, it follows that bond- stretch isomerism does not take place in cyanocyclobutadienes. Instead, these compounds exhibit rapid fluxional interconversion at room temperature between two bond-stretch isomers by the double bond flipping mechanism. The reason behind the decrease in the barrier heights is identified as a slightly enhanced resonance effect at the saddle points separating two (equivalent) bond-stretch isomers, compared to that in the equilibrium structures, predominantly due to the diradical character of the former. It is also shown that the energy gap between the singlet ground state saddle point structure and the first triplet equilibrium geometry decreases upon multiple substitution by the cyano groups. The splitting of the S and T energy is small being within the range of 6.5 – 8.2 kcal mol-1.

Izvorni jezik
Engleski

Znanstvena područja
Kemija



POVEZANOST RADA


Projekt / tema
098-0982933-2920 - Organski i bioorganski procesi u osnovnom i elektronski pobuđenim stanjima (Mirjana Maksić, )
098-0982933-2932 - Broenstedove i Lewisove kiseline i baze u kemiji i biokemiji (Robert Vianello, )

Ustanove
Institut "Ruđer Bošković", Zagreb

Profili:

Avatar Url Zvonimir Maksić (autor)

Avatar Url Mirjana Maksić (autor)

Avatar Url Mario Vazdar (autor)

Citiraj ovu publikaciju

Eckert-Maksić, Mirjana; Lischka, Hans; Maksić, Zvonimir B.; Vazdar, Mario
The Isomerization Barrier in Cyanocyclobutadienes: An ab Initio Multireference Average Quadratic Coupled Cluster Study // Journal of Physical Chemistry A, 113 (2009), 29; 8351-8358 doi:10.1021/jp9015273 (međunarodna recenzija, članak, znanstveni)
Eckert-Maksić, M., Lischka, H., Maksić, Z. & Vazdar, M. (2009) The Isomerization Barrier in Cyanocyclobutadienes: An ab Initio Multireference Average Quadratic Coupled Cluster Study. Journal of Physical Chemistry A, 113 (29), 8351-8358 doi:10.1021/jp9015273.
@article{article, year = {2009}, pages = {8351-8358}, DOI = {10.1021/jp9015273}, keywords = {ab initio calculations, antiaromaticity, isomerism, strained carbocycles}, journal = {Journal of Physical Chemistry A}, doi = {10.1021/jp9015273}, volume = {113}, number = {29}, issn = {1089-5639}, title = {The Isomerization Barrier in Cyanocyclobutadienes: An ab Initio Multireference Average Quadratic Coupled Cluster Study}, keyword = {ab initio calculations, antiaromaticity, isomerism, strained carbocycles} }

Časopis indeksira:


  • Current Contents Connect (CCC)
  • Web of Science Core Collection (WoSCC)
    • Science Citation Index Expanded (SCI-EXP)
    • SCI-EXP, SSCI i/ili A&HCI
  • Scopus
  • MEDLINE


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