MP2 and DFT Calculations on Circulenes and an Attempt to Prepare the Second Lowest Benzolog, [4]Circulene

Abstract

MP2 and DFT calculations have been carried out for [n]circulenes for n=3 to 20 in order to predict the strain energy and topology of these cyclically condensed aromatic systems. To synthesise [4]circulene (2), 1,5,7,8-tetrakis(bromomethyl)biphenylene (14) was prepared from the corresponding tetramethyl derivative (8) and subjected to various dehalogenation reactions; all attempts to obtain [2.2]biphenylenophane (7) as a precursor for 2 by this route failed. Treatment of 14 with sodium sulfide furnished the thiaphanes 16 and 17, thermal and photochemical desulfurization of which also failed to provide 7. In a second approach [2.2]paracyclophane was converted to the pseudo-geminal dithiol 23, which was subsequently bridged to the thiaphanes 22 and 24. On flash vacuum pyrolysis at 800 degrees C these were converted exclusively into phenanthrene (30). An approach to dehydrochlorinate the commercial product PARYLENE C to the tetrahydro[4]circulene 7 led only to polymerisation. The X-ray structures of the intermediates 8, 14, 17, 23, 24, 26, and 35 are reported.

Electronic structure, aromaticity and spectra of hetero[8]circulenes

“…This is why higher representatives of hydrocarbon circulenes were not isolated in the individual state and are studied by theoretical methods. 40 ± 43 Thus, it was shown 43 that an increase in the size of the macrocycle of benzo[n]circulenes (n = 9 ± 20) causes the helical twisting of their molecules, i.e., the saddle-shaped conformation is gradually transformed into the helical topology of the molecular skeleton of benzocirculenes.…”

“…The peripheral bond lengths d in hydrocarbon circulenes decrease from 1.403 to 1.338 # A in a series of circulenes 1 > 2 > 3 with an increase in the angular excess. In higher hydrocarbon [n]circulenes (n = 8 ± 20), starting with [8]circulenes 5, the macrocycle is substantially deformed and twisted, 43 resulting in that the length of the bonds d slightly varies and takes values close to 1.36 # A. In hetero [8]circulenes 7, 8, 11 and 12, the bond d is somewhat longer and its length varies in a range of 1.377 ± 1.398 # A depending on the nature of the heteroatom, except for TOC 8, in which the bond d is elongated due to the fusion with the benzene ring.…”

Sulfur monochloride in organic synthesis

“…130 It is believed that this compound is obtained from the stage of formation of a polysulfur-containing heterocycle from which a sulfur atom is eliminated, which has been proved by isolation of elemental sulfur from the reaction mass. The reaction of dithiole 200 with sulfur dichloride leads to the same trisulfide 201 in higher yield (96%) (Scheme 101).…”

Bottom‐up Approaches to Nanographenes through Organic Synthesis

“…The most prominent example of this group that has been successfully prepared is kekulene (1) [9]. Other macrocyclic polyarenes such as [10]circulene (2) [10] or [6] 10 cyclacene (3), a zigzag carbon nanotube subunit [11], have not been reported to date. Notably, the selective degradation of [60]fullerene led to a derivative of cyclo [10]phenacene (4) [12], which can be regarded as an armchair carbon nanotube subunit.…”

“…For example, the molecular formula of a cata-condensed 5, C 42 H 24 7, C 32 H 14 6, C 42 H 24 Figure 11.3 Three polyarenes with 10 fused benzene rings: [10]acene (5), [10]phenacene (6), and ovalene (7). In our opinion, this is a very intuitive approach for readers without a background in chemistry -a significant group within the graphene community.…”