Aromaticity Effects on the Profiles of the Lowest Triplet-State Potential-Energy Surfaces for Rotation about the CC Bonds of Olefins with Five-Membered Ring Substituents: An Example of the Impact of Baird's Rule
Artikel i vetenskaplig tidskrift, 2013

A density functional theory study on olefins with five-membered monocyclic 4n and 4n+2 -electron substituents (C4H3X; X=CH+, SiH+, BH, AlH, CH2, SiH2, O, S, NH, and CH-) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet-state ( (1)) potential-energy surface (PES) for twisting about olefinic CC bonds. It exploited both Huckel's rule on aromaticity in the closed-shell singlet ground state (S-0) and Baird's rule on aromaticity in the lowest * excited triplet state. 2CH(C4H3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C4H3X ring is bonded to the olefin. (0)-antiaromatic/ (1)-aromatic (C5H4+) to strongly S-0-aromatic/ (1)- antiaromatic (C5H4-). Our hypothesis is that the shapes of the (1) PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in (1) [E( (1))], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between E( (1)) and the (anti)aromaticity changes of the C4H3X groups, as measured by the zz-tensor component of the nucleus-independent chemical shift NICS( (1);1)(zz), are found both for sets A and B separately (linear fits; r(2)=0.949 and 0.851, respectively) and for the two sets combined (linear fit; r(2)=0.851). For sets A and B combined, strong correlations are also found between E( (1)) and the degree of S-0 (anti)aromaticity as determined by NICS(S-0,1)(zz) (sigmoidal fit; r(2)=0.963), as well as between the (1) energies of the planar olefins and NICS(S-0,1)(zz) (linear fit; r(2)=0.939). (1) PESs suitable for adiabatic Z/E photoisomerization.

alkenes

density functional calculations

aromaticity

photochemistry

electronic structure

Författare

J. Zhu

Uppsala universitet

State Key Laboratory of Physical Chemistry of Solid Surfaces (Xiamen University)

H. A. Fogarty

Uppsala universitet

Helene Möllerstedt

Chalmers, Kemi- och bioteknik, Organisk kemi

Maria Brink

Chalmers, Kemi- och bioteknik, Organisk kemi

H. Ottosson

Uppsala universitet

Chemistry - A European Journal

0947-6539 (ISSN) 1521-3765 (eISSN)

Vol. 19 32 10698-10707

Ämneskategorier

Organisk kemi

DOI

10.1002/chem.201300008