Chemistry Reference
In-Depth Information
designed and fine-tuned, e.g., by variation of the bridging groups X and Y, the
overcrowding in the fjord regions, extensions of the aromatic system, or other
modifications of the general BAE structure, based on the fundamental understand-
ing of the structure-property relationships (SPR). The present review provides an
analysis of the conformational spaces and the dynamic stereochemistry of
overcrowded bistricyclic aromatic enes applying fundamental symmetry consider-
ations. The symmetry analysis presented here allows deeper insight into the con-
formations, chirality, and the mechanisms of the dynamic stereochemistry, and will
be instrumental in future computational studies.
Keywords Conformations
Dynamic
stereochemistry
Intramolecular
overcrowding
Symmetry
Thermochromism and photochromism
Contents
1 Introduction .................................................................................. 179
1.1 Presentation of BAEs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
1.2 Scope of the Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
2 Overview of BAE Structures and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
2.1 Geometrical Parameters ............................................................... 181
2.2 Chirality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
2.3 X-Ray Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
2.4 BAE Variations ........................................................................ 187
2.5 Thermochromism, Piezochromism, Photochromism, and Electrochromism ....... 191
2.6 Dynamic Stereochemistry ............................................................. 195
2.7 Computational Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
2.8 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
3 Symmetry Analysis in Stereochemistry: General Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
3.1 Symmetry Operators and Permutation-Inversion Operators . . . . . . . . . . . . . . . . . . . . . . . . . 203
3.2 Historical Development of the Molecular Symmetry Group Approach . . . . . . . . . . . . 204
3.3 From the Complete Nuclear Permutation-Inversion Group to Feasible Operations
in the Molecular Symmetry Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
3.4 Transition State Symmetry . . . ......................................................... 205
3.5 Point Group Order and Number of Transition States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
3.6 Searching for Transition States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
3.7 Bifurcating Pathways . . . .............................................................. 208
4 Symmetry of BAEs .......................................................................... 210
4.1 Conformations and Point Groups of BAEs ........................................... 210
4.2 Symmetry and Dynamic Stereochemistry of BAEs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
4.3 Dynamic Stereochemistry of Homomerous BAEs . . ................................. 229
4.4 Symmetry of Heteromerous BAEs and Disubstituted Homomerous BAEs . . . ..... 262
5 Conclusions . ................................................................................. 263
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
