The subtle balance of weak supramolecular interactions: The hierarchy of halogen and hydrogen bonds in haloanilinium and halopyridinium salts

• Kari Raatikainen,
• Massimo Cametti and
• Kari Rissanen

Beilstein J. Org. Chem. 2010, 6, No. 4, doi:10.3762/bjoc.6.4

• tetrahedral anions such as dihydrogenphosphate. In addition, H2PO4− ion offers two OH groups providing two additional hydrogen bond donor sites differing from the corresponding anilinium halides, thus the interaction type ratio (D+–H···) : (C–I···) in 6 is 5 : 1. As the dihydrogenphosphate anion is a stronger

• between the molecular components can be influenced. The protonated pyridinium is a very strong hydrogen bond donor whereas the N-alkylated pyridinium is not. Thus the ratio of [N+–H···] and [C–I···], HB and XB, donor sites is 0 : 1 [N+–R] or 1 : 1 [N+–H]. To override the hydrogen bond contribution we

• strong hydrogen bond donor [N+–H···] moiety is envisaged to disrupt or severely hinder the strong halogen bonding interactions manifested in the non-HB pyridinium salt 9. Slow diffusion of ethyl acetate into the ethanol solution of 3-iodopyridinium chloride gave an X-ray-quality crystal of 10. The

Inversion symmetry and local vs. dispersive interactions in the nucleation of hydrogen bonded cyclic n-mer and tape of imidazolecarboxamidines

• Sihui Long,
• Venkatraj Muthusamy,
• Peter G. Willis,
• Sean Parkin and
• Arthur Cammers

Beilstein J. Org. Chem. 2008, 4, No. 23, doi:10.3762/bjoc.4.23

• polymers (tape) [9][10], cyclic n-mers [2][11][12], or dimers. For example, imidazolecarboxamidines 2 and imidazoles 3 have similar hydrogen bonding options offering sp2-NH hydrogen bond donors and sp2-N atom hydrogen bond acceptors. However 3 directs the hydrogen bond donor and acceptor approximately

• linearly [13] versus the ~90° intramolecular dihedral angle in 2. Large angles between hydrogen bond donor and acceptor, as in 3, should predispose solid state tapes [13], whereas small angles should prefer dimers. Planar motifs allow the favorable linearity in the hydrogen bond angles [14][15][16

• point [18] between 0° and 180° might likely afford a variety of hydrogen bonded motifs. To simplify the interplay between directionality and the motif of the crystalline phase n-mer we studied a molecule with one hydrogen bond donor and one acceptor. Motif diversity increases sharply with more donors or

Asymmetric aza-Diels- Alder reaction of Danishefsky's diene with imines in a chiral reaction medium

• Bruce Pégot,
• Olivier Nguyen Van Buu,
• Didier Gori and
• Giang Vo-Thanh

Beilstein J. Org. Chem. 2006, 2, No. 18, doi:10.1186/1860-5397-2-18

• results of these studies will be communicated in due course. Possible interactions of substrates or intermediate of the aza-Diels-Alder reaction with the chiral cation of an IL containing a hydrogen-bond donor. Asymmetric aza-Diels-Alder reaction of Danishefsky's diene 1 with imines 2. Asymmetric aza

Hydrogen bonding patterns in the cocrystals of 5-nitrouracil with several donor and acceptor molecules

• Reji Thomas,
• R. Srinivasa Gopalan,
• G. U. Kulkarni and
• C. N. R. Rao

Beilstein J. Org. Chem. 2005, 1, No. 15, doi:10.1186/1860-5397-1-15

• several hydrogen bond donor and acceptor sites, which provide a number of possibilities for hydrogen bonding. While the two-ring carbonyl oxygens and nitro-oxygens act as acceptors, the two NH groups along with the CH groups are donors. We present six hydrogen bonding possibilities in Scheme 1. Scheme 1a