Effects of substituents on the length of central C(sp³)–C(sp³) bond in anthracene photodimers and related molecules

Abstract

Effects of substituents on the lengths of the central C-C single bond in the butterfly-shaped anthracene photodimers (1 )- (7) and lepidopterenes (8) are studied. X-Ray analysis of the photodimer (1 0) of 9,1 0-difluoroanthracene gave a C(9)-C(1 0') bond length of 1.631 (3) A. An attempt to re-determine molecular structure of the photoisomer (5) of [2.2] (9, 1 O)anthracenophane (12) by neutron diffraction analysis is also reported [C(9)-C(10'): obs. 1.64(1 ), calc. 1.63(1) A]. The D 2 structure that had been proposed for the minimum-energy conformation of (5) -7 Although many investigators have assumed that steric repulsions between the two ring systems are responsible for the unusual lengthening of the central bond in these molecules, recent work has demonstrated that steric factors are not as important but the through-bond interaction among four aromatic rings aligned almost perpendicular to the C-C bond is responsible. 1 · 8 · 9 Among a number of possibilities, 1t--+O'* and 0--+1t* interactions destabilize and elongate the mediating C-C bond. A quantitative perturbational MO study has indicated that the former type dominates over the latter. It seems interesting to investigate further the relationship between the strength of these orbital interactions, the length of mediating bond, and the chemical consequences like reactivity.

Naphthocyclobutenes and Benzodicyclobutadienes: Synthesis in the Solid State and Anomalies in the Bond Lengths

“…[32] A nutation diffraction analysis of 59 showed that the central C-C bond length is actually 1.64(1) Å . [31] This is in perfect agreement with the calculated value of 1.64 Å . [31] X-ray analytical reinvestigations of 59 by two further research groups measured the central bond length at 1.663(4) [33] and 1.648(3) Å .…”

“…[31] This is in perfect agreement with the calculated value of 1.64 Å . [31] X-ray analytical reinvestigations of 59 by two further research groups measured the central bond length at 1.663(4) [33] and 1.648(3) Å . [34] Another error in the long C-C bond problem has happened for bisnorcaradienes (61).…”

“…[30] However, theoretical calculations did not support the data. [31] Finally, the extremely long bond in 59 was found to be an error. An X-ray analysis was performed for a mixture of 59 and 60 which had formed in a topotactic reaction.…”

Photodimerization of thioxanthone–anthracene: formation of monochromophoric Type II initiator

“…In the literature, based on the different substituents attached to anthracene, dimer proton is observed between 3.7 and 6.5. [28][29][30] While dimerization procedure was carried out under nitrogen atmosphere, δ 6.15-6.5 ppm protons belonging to endoperoxide formation were not observed. However, δ 4.00 ppm protons belong to bridgehead protons of photodimer product was seen as shown in Figure 4.…”

‘Face‐to‐Face’‐Benzo‐anellierte homologe Hypostrophene. Synthesen, Röntgenstrukturanalysen und PE‐Spektren

“…, . , 39,2 148,6 -152.8 dungsverlangerungen dieses Ausmasses in Kafigmolekulen sind ausfuhrlich diskutiert [27]. Die durch die Nachbarschaft der Benzo-Ringe bedingte sterische Spannung wird offensichtlich primar von diesen Bindungen aufgefangen, die Benzo-Ringe sind jedenfalls generell im Rahmen der Fehlergrenzen planar und die Anellierungspositionen nur schwach (2-3") In Fig.…”