TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Werner, Peter
A1  - Linker, Torsten
T1  - Synthesis and NMR spectroscopic conformational analysis of benzoic acid esters of mono- and 1,4-dihydroxycyclohexane, 4-hydroxycyclohexanone and the -ene analogue - The more polar the molecule the more stable the axial conformer
JF  - Tetrahedron
N2  - para-Substituted benzoic acid esters of cyclohexanol, 1,4-dihydroxycyclohexane, 4-hydroxy-cyclohexanone and of the corresponding exo-methylene derivative were synthesized and the conformational equilibria of the cyclohexane skeleton studied by low temperature H-1 and C-13 NMR spectroscopy. The geometry optimized structures of the axial/equatorial chair conformers were computed at the DFT level of theory. Only one preferred conformation of the ester group was obtained for both the axial and the equatorial conformer, respectively. The content of the axial conformer increases with growing polarity of the 6-membered ring moiety; hereby, in addition, the effect of sp(2) hybridization/polarity of C(4)= O/C(4)= CH2 on the present conformational equilibria is critically evaluated. Another dynamic process could be studied, for the first time in this kind of compounds. (C) 2017 Elsevier Ltd. All rights reserved.
KW  - Conformational analysis
KW  - A-values of COOAr on cyclohexane
KW  - Benzoic acid esters
KW  - Dynamic NMR
KW  - DFT calculations
Y1  - 2017
U6  - https://doi.org/10.1016/j.tet.2017.04.029
SN  - 0040-4020
VL  - 73
SP  - 3801
EP  - 3809
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Fudickar, Werner
A1  - Linker, Torsten
T1  - Theoretical insights into the effect of solvents on the [4+2] cycloaddition of singlet oxygen to substituted anthracenes
BT  - A change from a stepwise process to a concerted process
JF  - Journal of physical organic chemistry
N2  - The [4 + 2] cycloadditions of singlet oxygen to 9,10-diphenylanthracene (1) and the meta and para isomers of 9,10-dipyridylanthracene (2m/p) and 9,10-methoxyphenylanthracene (3m/p) have been studied by density functional calculations in the gas phase at the UB3LYP/6-31G* level and for the first time in solvents at the conductor-like polarizable continuum model (CPCM) UM062X/6-31G* level. The differences in calculated transition state (TS) energies derived from this method are in line with experimentally observed reactivity orders in solution. For the gas-phase reaction, the first TS of the stepwise pathway (TS1) has biradical character, and its energy lies below the energy of the TS of the concerted path (TSconc). In contrast, in the solvent acetonitrile, TS1 resembles a zwitterion and lies significantly higher than the TSconc. Thus, a concerted mechanism applies in solvents, and the energy gap between the TS of the two processes decreases with decreasing polarity. A change from a pyridyl against a methoxyphenyl substituent in the para position causes a maximal reduction of the activation barrier by approximately 1.7 kcal/mol, resulting in a fivefold increased reactivity.
KW  - anthracenes
KW  - DFT calculations
KW  - endoperoxides
KW  - photooxygenation
KW  - singlet oxygen
KW  - solvent effect
Y1  - 2019
U6  - https://doi.org/10.1002/poc.3951
SN  - 0894-3230
SN  - 1099-1395
VL  - 32
IS  - 7
PB  - Wiley
CY  - Hoboken
ER  -