Density Functional Theory Study of the Hydrogen Bond Interaction between Lactones, Lactams, and Methanol

Abstract

The structure and relative stability of methanol complexes with various cyclic ketones, lactones, lactams, and N-methyl lactams from three- to seven-membered rings have been investigated using the density functional theory method. The geometries, harmonic frequencies, and energies were calculated at the B3LYP/6-311+G(d,p) level. Three stable structures, cis-a, cis-b, and trans, with respect to the ring oxygen (nitrogen) atom, were found to be local minima of the potential energy surface. For lactones and N-methyl lactams, the most stable structure is trans; it is stabilized, as in cyclic ketones, through the conventional hydrogen bond (HB) interaction between the basic carbonyl oxygen and the acidic methanolic hydrogen and an unconventional HB interaction between the methanolic oxygen and the CH hydrogen, in the alpha position of the carbonyl group. For unsubstituted lactams, the cis-a structure, stabilized through a HB interaction between the NH group and the methanol oxygen in addition to the conventional HB interaction, is the most stable. The topological properties of the electron density ratify the existence of conventional (N,O-H. . .O) and unconventional (C-H. . .O) hydrogen bonding. A good correlation was found between the HB distances and the electron density at the HB critical point. The unsubstituted lactams yield more stable complexes with methanol than N-methyl lactams, lactones, and cyclic ketones. In the most stable complexes, both components behave simultaneously as a HB donor and as a HB acceptor.

Atomistic Model for the Polyamide Formation from β-Lactam Catalyzed by Candida antarctica Lipase B

“…DFT studies of El Firdoussi et al give an idea of the very different electronic structures and properties of lactones and lactams. 41 Assuming a mechanism for a ring-opening polymerization for lactones as we here postulate for β-lactam, the lactone polymerization should not be terminated as much as the lactam polymerization and, therefore, should yield a polymer of appreciable length. When there is no water present in the active site, there is no permanent competition between chain elongation and termination.…”

Characterization of indigo carmine with surface‐enhanced resonance Raman spectroscopy (SERRS) using silver colloids and island films, and theoretical calculations

“…Further, the shoulder at 511 cm 1 in the solid state (506 cm 1 in the solution) can be assigned to the outof-plane C-C-C and O CC bending modes, whereas the very weak band at 483 cm 1 in the solid state (481 cm 1 in the solution) is attributed to the skeletal distortion and the rocking modes of both the sulfonate groups. 53,70,72 In the lower wavenumber region, skeletal deformations and sulfonate group vibrations are observed ( Table 2, Fig. 4).…”

“…1(b)). The stable protonated structures of E132 are characterized by these two slightly stronger N C -HÐ Ð ÐO C hydrogen bonds, 50,53 which restrict the accessible conformational space. The intramolecular hydrogen bonds of E132, which are approximately 227 pm, are in competition with their intermolecular packing through the -stacks, which are held together by intermolecular hydrogen bonds.…”

Gas‐phase basicities of polyfunctional molecules. Part 1: Theory and methods

“…In a large sense, a hydrogen bond involves a hydrogen atom covalently bound to an electron deficient center, AH (or AH + ), and an acceptor center B (or B − ) including a non‐bonding lone pair or a π‐electrons system (Jeffrey, 1997; Scheiner, 1997; Gilli & Gilli, 2000; Sobczyk, Grabowski &, Krygowski, 2005). The proton donor part AH contains classically an electronegative atom but weak donors systems, such as certain CH, PH, … bonds, have been also identified and theoretically characterized (Scheiner, 1997; Desiraju & Steiner, 1999; Hartmann, Westmore, & Radom, 2001; Wetmore et al, 2001; El Firdoussi et al, 2005). To understand the consequences of hydrogen bonding in the basicity of polyfunctional compounds it is of interest to recall some results pertaining to bimolecular complexes, both neutral and protonated, bounded together by a hydrogen bond.…”