Intuitive Understanding of sigma Delocalization in Loose and sigma Localization in Tight Helical Conformations of an Oligosilane Chain

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F61388963%3A_____%2F17%3A00476131" target="_blank" >RIV/61388963:_____/17:00476131 - isvavai.cz</a>

Výsledek na webu

<a href="http://dx.doi.org/10.1002/asia.201700226" target="_blank" >http://dx.doi.org/10.1002/asia.201700226</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1002/asia.201700226" target="_blank" >10.1002/asia.201700226</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Intuitive Understanding of sigma Delocalization in Loose and sigma Localization in Tight Helical Conformations of an Oligosilane Chain

Popis výsledku v původním jazyce

Conformational effects on the sigma-electron delocalization in oligosilanes are addressed by Hartree-Fock and time-dependent density functional theory calculations (B3LYP, 6-311G**) at MP2 optimized geometries of permethylated uniformly helical linear oligosilanes (all--SinR2n+2) up to n=16 and for backbone dihedral angles =55-180 degrees. The extent of sigma delocalization is judged by the partition ratio of the highest occupied molecular orbital and is reflected in the dependence of its shape and energy and of UV absorption spectra on n. The results agree with known spectra of all-transoid loose-helix conformers (all-[+/- 165]-SinMe2n+2) and reveal a transition at approximate to 90 degrees from the sigma-delocalized limit at =180 degrees toward and close to the physically non-realizable sigma-localized tight-helix limit =0 with entirely different properties. The distinction is also obtained in the Huckel Ladder H and C models of sigma delocalization. An easy intuitive way to understand the origin of the two contrasting limits is to first view the linear chain as two subchains with alternating primary and vicinal interactions (sigma hyperconjugation), one consisting of the odd and the other of the even sigma(SiSi) bonds, and then allow the two subchains to interact by geminal interactions (sigma conjugation).

Název v anglickém jazyce

Intuitive Understanding of sigma Delocalization in Loose and sigma Localization in Tight Helical Conformations of an Oligosilane Chain

Popis výsledku anglicky

Conformational effects on the sigma-electron delocalization in oligosilanes are addressed by Hartree-Fock and time-dependent density functional theory calculations (B3LYP, 6-311G**) at MP2 optimized geometries of permethylated uniformly helical linear oligosilanes (all--SinR2n+2) up to n=16 and for backbone dihedral angles =55-180 degrees. The extent of sigma delocalization is judged by the partition ratio of the highest occupied molecular orbital and is reflected in the dependence of its shape and energy and of UV absorption spectra on n. The results agree with known spectra of all-transoid loose-helix conformers (all-[+/- 165]-SinMe2n+2) and reveal a transition at approximate to 90 degrees from the sigma-delocalized limit at =180 degrees toward and close to the physically non-realizable sigma-localized tight-helix limit =0 with entirely different properties. The distinction is also obtained in the Huckel Ladder H and C models of sigma delocalization. An easy intuitive way to understand the origin of the two contrasting limits is to first view the linear chain as two subchains with alternating primary and vicinal interactions (sigma hyperconjugation), one consisting of the odd and the other of the even sigma(SiSi) bonds, and then allow the two subchains to interact by geminal interactions (sigma conjugation).

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10401 - Organic chemistry

Projekt

—

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2017

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Chemistry-An Asian Journal

ISSN

1861-4728

e-ISSN

—

Svazek periodika

12

Číslo periodika v rámci svazku

11

Stát vydavatele periodika

DE - Spolková republika Německo

Počet stran výsledku

14

Strana od-do

1250-1263

Kód UT WoS článku

000402930000015

EID výsledku v databázi Scopus

2-s2.0-85019744566