Organic &
Biomolecular
Chemistry
Cite this: Org. Biomol. Chem., 2012, 10, 5747
COMMUNICATION
Facile air-oxidation of large aromatic hydrocarbon bay regions to bay region
quinones: predicted oxygen-sensitivity of hydrogen-terminated carbon
nanotubes†‡
Eric H. Fort and Lawrence T. Scott*
Received 27th January 2012, Accepted 8th February 2012
DOI: 10.1039/c2ob25208b
photocyclization.1 Intentional irradiation of an oxygen-saturated
Dimesitylbisanthene (1) oxidizes to the corresponding bay
solution of purified 1 in a quartz vessel with UV light cleanly
converts 1 to 2 in less than 30 minutes (Fig. 3). In Pyrex vessels,
which filter out most light of wavelengths shorter than 300 nm,
oxygen-saturated solutions of 1 still give 2 when irradiated with
UV light, though on a time scale of hours, rather than minutes.
Similarly, oxygen-saturated solutions of 1 in borosilicate NMR
tubes also yield 2 slowly upon irradiation with a 250 W reflector
incandescent bulb. In the solid state, dimesitylbisanthene (1) can
be exposed to air in ambient light for many weeks without any
significant oxidation, but solutions of 1 need to be protected
from oxygen and/or light. Derivatives of 1 that still have one
exposed bay region exhibit similar sensitivity to air and ambient
light.6
Bisanthenes that lack mesityl groups on the meso-positions
are highly susceptible to spontaneous oxidations that add
endoperoxide bridges across the central rings of the anthracene
units.7–9 As anticipated, the methyl groups at the 2- and 6-
positions of our mesityl substituents successfully block access to
the meso-carbon atoms and divert all Diels–Alder chemistry to
the bay regions.1,5
region quinone (2) on standing in solutions exposed to air
and ambient light. It is anticipated that hydrogen-terminated
carbon nanotubes with bay regions on the rim are likely to
exhibit even greater sensitivity toward air oxidation.
A Diels–Alder cycloaddition/rearomatization strategy has been
proposed as one potential method for elongating short, hydro-
carbon templates, such as hemispherical polyarenes and aromatic
belts, into full length, single-wall, single-index (n, m) carbon
nanotubes (n and m ≠ 0, Fig. 1).1–4 The feasibility of transform-
ing aromatic hydrocarbon bay regions into new, unsubstituted
benzene rings in a single operation, as required by this strategy,
has also been demonstrated recently, using the bay regions of
dimesitylbisanthene (1) as models for those on the rims of
carbon nanotubes and nitroethylene as a “masked acetylene”
(Fig. 2).5 Herein we report the inordinately high reactivity of
dimesitylbisanthene (1) toward bay region air oxidation, which
leads to bay region quinone 2 (Fig. 2).6 This finding signals a
warning about the potential oxygen-sensitivity of hydrogen-
terminated carbon nanotubes; a single oxidation of this sort on
the cylindrical rim of a growing carbon nanotube would preclude
further elongation of the tube by the Diels–Alder cycloaddition/
rearomatization protocol and would thereby terminate the
growth. Only hydrogen-terminated nanotubes of the (n, 0)
family (i.e., “zig-zag” nanotubes), which have no bay regions on
the rim, should be immune to such air oxidations; their lack of
bay regions, however, also renders them unsuitable for
elongation by the Diels–Alder cycloaddition/rearomatization
strategy.
Both oxygen and UV light (λ < 300 nm) are required for the
rapid bay region oxidation of dimesitylbisanthene (1). Quite
possibly, hydrocarbon 1 serves as a good photosensitizer to
Quinone 2 was first discovered as a by-product from the syn-
thesis of 1, the last step of which involves an oxidative
Merkert Chemistry Center, Department of Chemistry, Boston College,
Chestnut Hill, MA 02467-3860, USA. E-mail: lawrence.scott@bc.edu;
Fax: +617-552-6454; Tel: +617-552-8024
†This article is part of the Organic & Biomolecular Chemistry 10th
Anniversary issue.
‡Electronic supplementary information (ESI) available: Experimental
details, spectra for quinone 2, and CIF file for the X-ray crystal structure
of quinone 2. CCDC 865170. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2ob25208b
Fig. 1 Basic steps of the proposed Diels–Alder cycloaddition/rearoma-
tization nanotube growth process, shown formally with acetylene.
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 5747–5749 | 5747
Fort, Eric H.
