88 research outputs found
25,26-Bis(propan-2-ylÂidene)heptaÂcyclo[20.2.1.110,13.02,21.03,8.09,14.015,20]hexaÂcosa-2(21),3,5,7,9(14),11,15,17,19,23-decaÂene
In the title compound, C32H28, the central cycloÂoctaÂtetraÂene ring has a boat conformation, and the molÂecule is saddle shaped. The seat is defined by the mean plane of the four-atom attachment points (r.m.s. deviation = 0.014 Å) of the two bicycloÂheptenyl substituents. These substituents comprise the pommel and cantle, with each mean plane defined by four atoms proximate to the seat (r.m.s. deviations = 0.002 and 0.004 Å). Relative to the seat, the pommel and cantle bend up 31.16 (4) and 29.40 (5)°, while the benzo units (flaps, r.m.s. deviations = 0.006 and 0.009 Å) bend down 36.75 (4) and 38.46 (4)°. The mean planes of the dimethylÂethylÂidene units are almost perpendicular to the saddle seat, making dihedral angles 86.89 (4) and 88.01 (4)°
Weighting non-covalent forces in the molecular recognition of C60. Relevance of concave–convex complementarity
The relative contributions of several weak intermolecular forces to the overall stability of the complexes formed between structurally related receptors and [60]fullerene are compared, revealing a discernible contribution from concave–convex complementarity.Viruela Martin, Pedro Manuel, [email protected] ; Viruela Martin, Rafael, [email protected] ; Orti Guillen, Enrique, [email protected]
Search for corannulene (C20H10) in the Red Rectangle
Polycyclic Aromatic Hydrocarbons (PAHs) are widely accepted as the carriers
of the Aromatic Infrared Bands (AIBs), but an unambiguous identification of any
specific interstellar PAH is still missing. For polar PAHs, pure rotational
transitions can be used as fingerprints for identification. Combining dedicated
experiments, detailed simulations and observations, we explored the mm domain
to search for specific rotational transitions of corannulene (C20H10). We
performed high-resolution spectroscopic measurements and a simulation of the
emission spectrum of UV-excited C20H10 in the environment of the Red Rectangle,
calculating its synthetic rotational spectrum. Based on these results, we
conducted a first observational campaign at the IRAM 30m telescope towards this
source to search for several high-J rotational transitions of (C20H10). The
laboratory detection of the J = 112 <- 111 transition of corannulene showed
that no centrifugal splitting is present up to this line. Observations with the
IRAM 30m telescope towards the Red Rectangle do not show any corannulene
emission at any of the observed frequencies, down to a rms noise level of Tmb =
8 mK for the J =135 -> 134 transition at 137.615 GHz. Comparing the noise level
with the synthetic spectrum, we are able to estimate an upper limit to the
fraction of carbon locked in corannulene of about 1.0x10(-5) relative to the
total abundance of carbon in PAHs. The sensitivity achieved shows that radio
spectroscopy can be a powerful tool to search for polar PAHs. We compare this
upper limit with models for the PAH size distribution, emphasising that small
PAHs are much less abundant than predicted. We show that this cannot be
explained by destruction but is more likely related to the chemistry of their
formation in the environment of the Red Rectangle.Comment: 8 pages, 7 figures, 2 tables, accepted for publication in MNRA
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