Herein, we report that the conformational preference of phenyla cetate is governed by steric effect and n! p*i nteraction. Conformation-specifice lectronic and IR spectroscopy combined with quantum chemistry calculations confirm the presence of only the cis conformer of phenyl acetate in the experiment. The cis conformer of phenyl acetate hasn !p*i nteraction betweent he lone-pair electrons on the carbonyl oxygen atom and the p*o rbitals of the phenyl group. The n!p*i nteraction is absent in the trans conformer whichh as additional steric repulsion between the methyl group and phenyl ring. The trans conformer is higher in energyt han the cis conformer by % 3kcal mol À1 .W eh ave found the effect of methyl substitution on the strength of the n!p*i nteraction, steric repulsion, and hyperconjugation in phenyla cetate. The red-shift observed in the cis conformer of phenyl acetate with respect to the trans conformer is affected due to the influence of the methyl substituent on the strength of the n!p*i nteraction as well as hyperconjugation.T he present result demonstrates that the introduction of abulkiersubstituent can induce steric as wellase lectronic control to reduce conformational heterogeneity of a molecular system. Understanding the effect of bulkiers ubstituents to promote defined conformations having specific non-covalent interactions may have implicationi nb etter perception of the optimum structure and function of biomolecules as well as recognition of drugs by biomolecules.[a] Dr.
The
S–H···S non-covalent interaction is generally
known as an extremely unconventional weak hydrogen-bond in the literature.
The present gas-phase spectroscopic investigation shows that the S–H···S
hydrogen-bond can be as strong as any conventional hydrogen-bond in
terms of the IR red-shift in the stretching frequency of the hydrogen-bond
donor group. Herein, the strength of the S–H···S
hydrogen-bond has been determined by measuring the red-shift (∼150
cm–1) of the S–H stretching frequency in
a model complex of 2-chlorothiophenol and dimethyl sulfide using
isolated gas-phase IR spectroscopy coupled with quantum chemistry
calculations. The observation of an unusually large IR red-shift in
the S–H···S hydrogen-bond is explained in terms
of the presence of a significant amount of charge-transfer interactions
in addition to the usual electrostatic interactions. The existence
of ∼750 S–H···S interactions between
the cysteine and methionine residues in 642 protein structures determined
from an extensive Protein Data Bank analysis also indicates that this
interaction is important for the structures of proteins.
A series of triazole–cyanostilbene
receptors were designed
and synthesized. The receptor binds with the anions through various
CH···anion hydrogen bonding interactions, where strong
binding was observed for SO4
2– anions
followed by Cl–, Br–, NO3
–, and I–, calculated from the 1H NMR titration experiment. The NOESY NMR experiment of the
receptor confirmed the formation of anion-induced folded conformation.
The CH···anion hydrogen bonding interaction-mediated
anion recognition and foldamer formation were further confirmed from
geometry optimization studies of the anion-bound complex. The receptor
transports Cl– anions efficiently compared to SO4
2– anions across the lipid bilayer membrane
via a mobile carrier mechanism.
Herein,
we report the synthesis of a series of bis(silanechalcogenones)
[Ch = Te (2), S (3), or Se (4)] using an N-heterocyclic silylene-based SiCSi pincer ligand (1). 2 is the first example of a bis(silanetellurone)
derivative. The bonding patterns of 2–4 were extensively
studied by natural bond orbital, quantum theory of atoms in molecules,
and noncovalent interaction index analyses, and these exhibit weak
C–H···Ch interaction. The analogous reaction
of 1 with trimethyl N-oxide produced
a novel bis(cyclosiloxane) derivative (5). All of the
complexes are duly characterized by single-crystal X-ray diffraction
studies, multinuclear nuclear magnetic resonance (1H, 13C, and 29Si) spectroscopy, and high-resolution
mass spectrometry.
Herein, a perspective on the recent understanding of weak n→π* interaction from different experimental and theoretical approaches is presented. This interaction is purely an orbital interaction that involves the delocalization...
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