Dissection of the Factors Affecting Formation of a CH∙∙∙O H-Bond. A Case Study

Abstract

Quantum calculations are used to examine how various constituent components of a large molecule contribute to the formation of an internal CH···O H-bond. Such a bond is present in the interaction between two amide units, connected together by a series of functional groups. Each group is removed one at a time, so as to monitor the effect of each upon the H-bond, and thereby learn the bare essentials that are necessary for its formation, as well as how its presence affects the overall molecular structure. Also studied is the perturbation caused by change in the length of the aliphatic chain connecting the two amide groups. The energy of the CH···O H-bond is calculated directly, as is the rigidity of the entire molecular framework.

Halogen-Bonded Co-Crystals of Aromatic N-oxides: Polydentate Acceptors for Halogen and Hydrogen Bonds

“…Further analysis of the crystal packing revealed the donor-acceptor parallel arrangement to be a result of F···F aggregation [38][39][40][41][42] between perfluorinated donor chains, which, though weaker than C−I···O − −N + XBs, play a crucial role to yield a robust 3-D crystal structure. The strength of the C−H···O interaction is approximately one-third of conventional HBs [43][44][45][46][47][48][49] that operate between donors such as −N−H/−O−H and weak bases, and these interactions significantly increase the lattice energy of the co-crystals [50]. The C−H···O contacts are attractive, and are rather site acidity-dependent.…”

“…For example, in 3•DI4, the N−O group bridged donors at I···O distances of ca. The strength of the C−H···O interaction is approximately one-third of conventional HBs [43][44][45][46][47][48][49] that operate between donors such as −N−H/−O−H and weak bases, and these interactions significantly increase the lattice energy of the co-crystals [50]. The C−H···O contacts are attractive, and are rather site acidity-dependent.…”

Looking Inside the Intramolecular C−H∙∙∙O Hydrogen Bond in Lactams Derived from α-Methylbenzylamine

“…Indeed, today its relevance and importance in chemistry is fundamental to the interpretation and understanding of molecular conformation (either in solution or in the solid state [ 8 ]) and of chemical transformations in solution. Although this interaction does not usually exceed 3 kcal/mol [ 9 , 10 ], it plays a crucial role in favoring crystallization [ 11 , 12 ], conformational equilibrium [ 13 , 14 ] or inducing selectivity [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. In this context, a recent report which describes the role of the intramolecular C−Hα···O contact of chiral lactams (derived from the α-methylbenzylamine) in their spatial arrangement—both in solution and in solid state [ 23 ]—have attracted our attention, especially because this chiral auxiliary is frequently employed in asymmetric synthesis [ 24 ].…”

Assessment of the Presence and Strength of H-Bonds by Means of Corrected NMR

“…Over the years, quite a number of markers have been developed [20,21,22,23,24,25] by which to identify the presence of a H-bond (HB). There is first a set of geometric criteria, in which the A and B atoms of the putative AH··B HB must lie within a cutoff distance.…”