Study on Conformation Interconversion of 3-Alkyl-4-acetyl-3,4-dihydro-2H-1,4-benzoxazines from Dynamic NMR Experiments and ab Initio Density Functional Calculations

Through-space π-delocalization in a conjugated macrocycle consisting of [2.2]paracyclophane

Herein, we report the synthesis and characterization of a [2.2]paracyclophane-containing macrocycle (PCMC) as a new through-space conjugated macrocycle using only benzene groups as the skeleton. For comparison, a diphenylmethane-containing nanohoop macrocycle (DCMC) with a non-conjugated linker was also synthesized. Their structures were confirmed by NMR and HR-MS, and their photophysical properties were studied by UV-vis and fluorescence spectroscopies combined with theoretical calculations. The strain energy of PCMC was estimated to be as high as 72.58 kcal mol-1.

Noncovalent Interactions of Fluorine with Amide and CH2 Groups in N-Phenyl γ-Lactams: Covalently Identical Fluorine Atoms in Nonequivalent Chemical Environments

We designed and synthesized N-phenyl γ-lactam derivatives possessing two covalently identical ortho-F nuclei on the N-phenyl group. The F nuclei sited in different chemical environments where they were spatially adjacent to amide and alkyl groups due to hindered rotation around the central N-Ar bond. ¹⁹F NMR spectroscopic and X-ray crystallographic methods were used to distinguish the axially prochiral F nuclei and provide structural insights for through-space interactions between F and amide/CH₂ groups. Direct spectroscopic evidence for multipolar interactions in F···amide and F···CH₂ pairs were provided.

Stabilization of amino acid zwitterions with varieties of anionic species: the intrinsic mechanism

With high-level ab initio theoretical methods, varieties of novel anions (two monoanions and dianions with two binding sites) were explored to stabilize the glycine zwitterions. Unlike the malonic and oxalic dianions (J. Am. Chem. Soc. 2005, 127, 13098.), the presently found anions are self-stable and widely available, ensuring the direct and convenient applications to stabilize the zwitterions. Some of the complexes formed with the anions and glycine zwitterions have very large vertical dissociation energies (>500.0 kJ mol (-1)), implying that the contained anions can be used to stabilize much more unstable zwitterions than the glycine zwitterions. Further studies revealed that the stabilization effects are closely related with the proton-capturing capacities of the anions. In order to stabilize the glycine zwitterions, the proton affinity (PA) of the anionic species should fall within the range of 1567.0-1983.6 kJ mol (-1) and, meanwhile, the proton-affinity differences of the two binding sites (DeltaPA) should be less than 104.2 kJ mol (-1). The present results can be used to direct the efficient designs of the stabilizers to other amino acid zwitterions as well as other types of zwitterions. In addition, the density functional theory was used and compared with the default MP2 theory, with the details given in the discussions.