Conformations of 2-Aminoindan in a Supersonic Jet:  The Role of Intramolecular N−H···π Hydrogen Bonding

Iga, Hiroshi; Isozaki, Tasuku; Suzuki, Tadashi; Ichimura, Teijiro

doi:10.1021/jp072072j

Cited by 21 publications

(17 citation statements)

References 49 publications

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“…The weak non-bonded interactions of the p electron cloud of aromatic molecules with hydrogen atoms of the C-H, N-H, and O-H bonds have been the subject of several experimental and theoretical investigations [1][2][3][4][5][6][7]. These interactions play an important role in determining the conformational preferences of molecules and clusters [1][2][3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

“…These interactions play an important role in determining the conformational preferences of molecules and clusters [1][2][3][4][5][6][7]. The interactions are mediated by dispersion and electrostatic forces; the latter are more important in the case of polar N-H and O-H bonds [4].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, a large number of conformationally flexible derivatives of indan have been investigated with the primary aim of determining the factors governing the A. Hamza (&) Petroleum Chemistry and Engineering Program, School of Arts and Sciences, American University of Nigeria, PMB 2250 Yola, Nigeria e-mail: abdulhamid.hamza@aun.edu.ng conformational stabilities of organic molecules [2,3,6,7,[12][13][14]. Only two of the six stable conformers of 1-aminoindan were observed in the supersonic jet experiments of Isozaki et al [3].…”

Section: Introductionmentioning

confidence: 99%

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Molecular conformations of jet-cooled 2-methylindan and 2-phenylindan

Hamza

2010

Struct Chem

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The molecular conformations of jet-cooled 2-methylindan (2MI) and 2-phenylindan (2PI) have been studied using resonant-enhanced two-photon ionization spectroscopy in combination with ab initio calculations. Both axial (2MI ax ) and equatorial (2MI eq ) conformers of 2MI have been observed. A 2MI eq /2MI ax conformer ratio of 2.3 was estimated at 298 K, leading to the energy difference, DE ¼ E 2MI ax À E 2MI eq , of 0.49 kcal/mol. Ab initio calculations predicted three stable conformers of 2PI: two equatorial conformers (2PI eq0 and 2PI eq90 ), and one axial conformer (2PI ax ). Only the axial conformer of 2PI (2PI ax ) was experimentally observed. The indan ring of 2PI ax is slightly more planar than the indan rings of the two equatorial conformers of 2PI because of the intramolecular C sp2 -H/p interactions in 2PI ax . The equatorial conformers of 2PI relax to the more stable axial conformer because of the high pre-expansion temperature (383 K), and relatively low barrier (1.68 kcal/mol) to axial-equatorial interconversion. The barrier (2.33 kcal/mol) to axial-equatorial interconversion in 2MI is high enough to prevent conformational relaxation at the pre-expansion temperature of 298 K. Intramolecular C-H/p interactions are found to be more important in determining the conformational preference of 2PI than 2MI; this can be attributed to the higher acidity of the C sp2 -H bond than that of C sp3 -H bond.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular conformations of jet-cooled 2-methylindan and 2-phenylindan

Hamza

2010

Struct Chem

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“…Weak H-bonds should be considered when examining molecular structures of fluxional molecules and their stabilization energies. Frequencies of purely electronic S 0 -S 1 -transitions of organic molecular structures vary from units to tens of inverse centimeters [1][2][3]. This makes it possible to use jet cooling to identify these conformers.…”

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confidence: 99%

“…These are elongated structures V and VI (the group is at a distance from the indole ring); I and IV (the group is twisted toward the indole ring); and II and III (the group is twisted away from the indole ring). The Si(CH 3 It is well known that the number of conformers and their stabilization energies that are obtained theoretically depend on the computation method [10]. The MP2 method takes into account correctly dispersive interactions [11].…”

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confidence: 99%

Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

et al. 2010

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UDC 535.37Conformations of He-jet-cooled trimethyl [(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S 0 -S 1 transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds C-H⋅⋅⋅O< C Si between hydrogen atoms of methyl groups and an oxygen atom and C-H⋅⋅⋅π between H and the π-electron cloud of the indole ring.Introduction. The non-classical hydrogen bond, interaction between an H atom (bound to one of the electronegative C, O, or N atoms) and the π-electron cloud of an aromatic ring, has been widely studied in the last decade. Such weak non-covalent bonds are formed intramolecularly [1-3] or intermolecularly [4,5] in van-der-Waals complexes in biological systems. Weak H-bonds should be considered when examining molecular structures of fluxional molecules and their stabilization energies. Frequencies of purely electronic S 0 -S 1 -transitions of organic molecular structures vary from units to tens of inverse centimeters [1][2][3]. This makes it possible to use jet cooling to identify these conformers. Various methods of laser UV and IR spectroscopy are used in such investigations. The preferred structures can be determined when they are combined with modern quantum-chemical computation methods.Herein we analyze the molecular structures of trimethyl[(3-indole)ethoxy]silane (TIES) and examine the effect of an intramolecular H-bond on the stabilization energy of its conformers.Experimental. Fluorescence excitation and fluorescence spectra were measured using the automated spectrometry complex that was described before [6]. The carrier gas, He at a pressure of 2 atm, was fed into a prechamber heated to 400 K that contained saturated TIES vapor. The liquid organic compound was placed into capillaries (0.75 internal diameter, 30 mm long). The number of capillaries was selected so that the optimal luminescence signal was obtained. A pulsed supersonic stream was formed by flowing the gas mixture into the vacuum chamber through a round nozzle (diameter 0.7 mm). The cooled molecules were excited by the second harmonic of a frequency-tuned dye laser at distances of 19 and 10 mm from the nozzle for recording fluorescence excitation and fluorescence spectra, respectively. The dye laser was pumped by the second harmonic of a Nd-doped yttrium-aluminum garnet laser (LOTIS TII, LS-2134). The wavelengths of the first harmonic of the dye laser were calibrated using the fluorescence excitation spectrum of iodine vapor. Integral fluorescence was recorded using a Hamamatsu R928 photoelectron multiplier. A DFS-52 monochromator with a diffraction grating (2400 lines/mm) was used to study the fluores...

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Conformational analysis and intramolecular hydrogen bonding of cis-3-aminoindan-1-ol: a quantum chemical study

et al. 2013

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In the present work, we carried out a conformational analysis of cis-3-aminoindan-1-ol and evaluated the role of the intramolecular hydrogen bond in the stabilization of various conformers using quantum mechanical DFT (B3LYP) and MP2 methods. On the basis of relative energies, we have found nine conformational minima, which can interchange through the ring-puckering and the internal rotation of the OH and NH2 groups on the five-membered ring. The intramolecular hydrogen bonds such as OH∙∙∙∙π, NH∙∙∙∙π, NH∙∙∙∙OH and HN∙∙∙∙HO are expected to be of critical importance for the conformational stabilities. The intramolecular interactions of the minima have been analyzed by calculation of electron density (ρ) and Laplacian (ρ) at the bond critical points (BCPs) using atoms-in-molecule (AIM) theory. The existence or absence of OH∙∙∙∙π and NH∙∙∙∙π in cis-3-aminoindan-1-ol remains unclear since the geometrical investigation has not been confirmed by topological criteria. The results of theoretical calculations demonstrate that this compound exists predominantly in one ring-puckering form stabilized by strong hydrogen bond HN∙∙∙∙HO Interaction.

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Conformations of 2-Aminoindan in a Supersonic Jet: The Role of Intramolecular N−H···π Hydrogen Bonding

Cited by 21 publications

References 49 publications

Molecular conformations of jet-cooled 2-methylindan and 2-phenylindan

Molecular conformations of jet-cooled 2-methylindan and 2-phenylindan

Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

Conformational analysis and intramolecular hydrogen bonding of cis-3-aminoindan-1-ol: a quantum chemical study

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