1,852 research outputs found
Intermolecular N-H...O=C hydrogen bonding in the crystal structure of 6-amino-1,3-dimethyluracil
The 6-amino- 1,3-dimethyluracil molecule [6-amino- 1,3-
dimethyl-2,4(1H,3H)-pyrimidinedione], C6H9N302 (I),
lies on a crystallographic mirror plane and participates
in an extensive two-dimensional hydrogen-bonding network
in the solid state. Each molecule is involved in N--
H...O=C hydrogen bonding involving the amino and
carbonyl gr. oups, with O...N separations of 2.894 (3) and
2.904 (3) A
The structure of triphenylmethanol, Ph₃COH
C19H160 , Mr = 260.3, trigonal, R3, a =
19.307 (3), c = 26.735 (4) A, V= 8631 (2) A 3, Z= 24,
Dx = 1.20 g cm -3, a(Mo Ka) = 0.71073/~, /.~ =
0.7 cm -1, F(000) = 3312, T = 294 K, R = 0.083, wR
= 0.068 for 1022 observed reflections. The structure
contains hydrogen-bonded pyramidal tetramers
(which have approximate 32 symmetry) with one
molecule lying on a crystallographic threefold axis
and another in a general position. The analysis was
complicated by disorder in the crystal lattice where
71% of the tetramers occupy one orientation and
29% another; these moieties have their phenyl rings
in the same volume elements in the lattice. The O...O
separations in the hydrogen-bond systems are
2.884 (10) and 2.896 (11)/~ in the major tetramer
and 2.80 (3) and 2.90 (3) A in the minor tetramer
What can the L3 events be?
We consider the 4 () events reported by the L3
collaboration, and go through the logical possibilities which could explain the
events. If they are not coincidental bremsstrahlung events, we find that the
physics which they could point to is extremely limited. One possibility would
be to have a new 60 GeV scalar (or pseudoscalar) particle with an
off-diagonal coupling to a and which is non-perturbative (), where the couplings to are suppressed. One could also
construct a model involving , and a second scalar with a large
coupling. We do not promote either of these models, but hope they would
prove to be useful guidelines, should the L3 events turn out to be new physics.Comment: 7 pp (3 fig avail. on request), LATEX, TRI-PP-92-12
2,4,5-Tris(biphenyl-2-yl)-1-bromobenzene
In the title compound, C42H29Br, the dihedral angles between the central benzene ring and the three attached benzene rings are very similar, lying in the range 52.65 (6)–57.20 (7)°. Of the dihedral angles between the rings of the o-biphenyl substituents, two are similar [46.34 (7) and 47.35 (7)°], while the other differs significantly [64.17 (7)°]. In the crystal, molecules are linked into centrosymmetric dimers by two weak C—H⋯π interactions
Crystal structures and Hirshfeld surfaces of four methoxybenzaldehyde oxime derivatives, 2-MeO-XC6H3C=NOH (X = H and 2-, 3- and 4-MeO): different conformations and hydrogen-bonding patterns
The crystal structures of four (E)-meth-oxy-benzaldehyde oxime derivatives, namely (2-meth-oxy-benzaldehyde oxime, 1, 2,3-di-meth-oxy-benzaldehyde oxime, 2, 4-di-meth-oxy-benzaldehyde oxime, 3, and 2,5-di-meth-oxy-benzaldehyde oxime, 4, are discussed. The arrangements of the 2-meth-oxy group and the H atom of the oxime unit are s-cis in compounds 1-3, but in both independent mol-ecules of compound 4, the arrangements are s-trans. There is also a difference in the conformation of the two mol-ecules in 4, involving the orientations of the 2- and 5-meth-oxy groups. The primary inter-molecular O-H(oxime)⋯O(hy-droxy) hydrogen bonds generate C(3) chains in 1 and 2. In contrast, in compound 3, the O-H(oxime)⋯O(hy-droxy) hydrogen bonds generate symmetric R22(6) dimers. A more complex dimer is generated in 4 from the O-H(oxime)⋯O(hy-droxy) and C-H(2-meth-oxy)⋯O(hy-droxy) hydrogen bonds. In all cases, further inter-actions, C-H⋯O and C-H⋯π or π-π, generate three-dimensional arrays. Hirshfeld surface and fingerprint analyses are discussed.info:eu-repo/semantics/publishedVersio
Crystal structures, Hirshfeld surface analysis and a computational study of four ethyl 2-oxo-2H-chromene-3-carboxylate derivatives : a survey of organyl 2-oxo-2H-chromene-3-carboxylate structures
LRG thanks the Portuguese Foundation for Science and Technology (FCT) UID/Multi/04546/2013.for support. TvM is grateful to EaStCHEM for computational support via the EaStCHEM Research Computing Facility. JLW thanks CNPq, Brazil for support.Crystal structures, Hirshfeld surface analysis and a computational study have been carried out on 2-oxo-2H-chromene-3-carboxylates. Crystal structures are reported for ethyl R-2-oxo-2H-chromene-3-carboxylate derivatives, 2a: R=6-Me, 2b: 7-Me, 2c: 7-Me, 2d: R=7-MeO. In contrast to 2-oxo-2H-chromene-3-carboxamides, 1, in which classical intramolecular N–H···O hydrogen bonds stabilize planar structures and hinder rotation of the amido group out of the coumarin plane in 2, without an equivalent hydrogen bond, there is a greater rotational freedom of the carboxylate group. The interplanar angles between the coumarin core and its attached –C(O)–R substituent in crystalline 2a, 2b, 2c and 2d are 10.41(6), 36.65(6), 10.4(2) and 5.64(6)°, respectively, with distances between the carbonyl oxygen atoms of 2.8255(16), 2.9278(16), 4.226(2) and 2.8328(14) Å, respectively. A theoretical study of molecular conformations was carried out at the M06-2X density level with the 6-31+G(d) and aug-cc-pVTZ basis sets, in methanol solution modeled by PCM, indicated that the most stable conformations had the carbonyl group of the ester in the plane of the coumarin core: the s-cis arrangement of the ester carbonyl and the 2-oxo moieties being the slightly more stable than the s-trans form by less than 0.5 kcal/mol. The experimental conformations of 2a and 2d match well the low energy s-cis arrangement, and 2c matches the slightly lesser stable s-trans arrangement found in the theoretical study. A survey of the molecular conformations of more than 50 2H-chromene-3-carboxylates derivatives in the CCDC data base indicated two distinct groupings of conformations, s-cis and s-trans, each with interplanar angles <30°.Publisher PDFPeer reviewe
Different classical hydrogen-bonding patterns in three salicylaldoxime derivatives, 2-HO-4-XC6H3C=NOH (X = Me, OH and MeO)
The crystal structures of three salicyaldoxime compounds, namely 2-hy-droxy-4-methyl-benzaldehyde oxime, C8H9NO2, 1, 2,4-di-hydroxy-benzaldehyde oxime, C7H7NO3, 2, and 2-hy-droxy-4-meth-oxy-benzaldehyde oxime, C8H9NO3, 3, are discussed. In each compound, the hydroxyl groups are essentially coplanar with their attached phenyl group. The inter-planar angles between the C=N-O moieties of the oxime unit and their attached phenyl rings are 0.08 (9), 1.08 (15) and 6.65 (15)° in 1, 2 and 3, respectively. In all three mol-ecules, the 2-hy-droxy group forms an intra-molecular O-H⋯N(oxime) hydrogen bond. In compound (1), inter-molecular O-H(oxime)⋯O(hydrox-yl) hydrogen bonds generate R22(14) dimers, related by inversion centres. In compound 2, inter-molecular O-H(oxime)⋯O(4-hy-droxy) hydrogen bonds generate C9 chains along the b-axis direction, while O-H(4-hydrox-yl)⋯O(2-hydrox-yl) inter-actions form zigzag C6 spiral chains along the c-axis direction, generated by a screw axis at 1, y, 1/4: the combination of the two chains provides a bimolecular sheet running parallel to the b axis, which lies between 0-1/2 c and 1/2-1 c. In compound 3, similar C9 chains, along the b-axis direction are generated by O-H(oxime)⋯O(4-meth-oxy) hydrogen bonds. Further weaker, C-H⋯π (in 1), π-π (in 2) and both C-H⋯π and π-π inter-actions (in 3) further cement the three-dimensional structures. Hirshfeld surface and fingerprint analyses are discussed.info:eu-repo/semantics/publishedVersio
4-(1-Naphthyl)benzoic acid
In the title molecule, C17H12O2, the dihedral angle between the mean plane of the benzene ring and that of the naphthalene ring system is 49.09 (6)°. In the crystal structure, molecules are linked to form centrosymmetric dimers via intermolecular O—H⋯O hydrogen bonds. The hydroxy H atom is disordered over two sites with refined occupancies of 0.62 (3) and 0.38 (3)
- …