A study on aromatic C–H⋯X (X=N, O) hydrogen bonds in 1,2,4,5-tetrafluorobenzene clusters using infrared spectroscopy and ab initio calculations

Venkatesan, V.; Fujii, Asuka; Mikami, Naohiko

doi:10.1016/j.cplett.2005.04.079

“…This hypothesis is consistent with calculations and experimental data showing that polarized aromatic molecules, such as tetrafluorobenzene, can form relatively strong CÀH···O bonds. [20] The observation that the substituted ring of methylnaphthalene is not strongly activated towards CÀH···O bonding is consistent with the fact that all effective modifiers for the Orito reaction contain multiple-ring aromatic groups.…”

supporting

confidence: 60%

Chemisorption‐Induced Double Hydrogen Bonding, Self‐Assembly, and Stereoselection

Lavoie

¹

,

Mahieu

²

,

McBreen

³

2006

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By carefully choosing molecular components, it is possible to design supramolecular assemblies on metal surfaces for a variety of applications ranging from templating to asymmetric catalysis. [1][2][3] The choice of molecular building blocks is based on the fundamental chemical concept of functional groups; hydrogen-bond donor-acceptor pairs have proven exceptionally useful for self-assembly. [4][5][6] Hence, it is crucial to recognize that associative chemisorption can generate hydrogen-bond donor functionality in molecules for which hydrogen bonding is negligible in the gas or solution-phase. [7,8] Herein, we report that nonsubstituted arenes form strong C À H···O hydrogen bonds to co-adsorbed esters and ketoesters on Pt(111) surfaces. Scanning tunneling microscopy (STM) imaging is used to isolate well-defined aryl-carbonyl assemblies at 150-300 K and to identify the interaction that binds them as double hydrogen bonding. In this way, chemisorption-activated arenes are found to combine two powerful properties for 2D self-assembly: planarity and double hydrogen bonding. Furthermore, the direct observation of aryl-carbonyl CÀH···O interactions supports a new mechanism for the stereoselective hydrogenation of ketoesters on cinchona-modified platinum. [7] In turn, the observation also suggests that aryl C À H···X bonding, where X is a hydrogen-bond acceptor, should be explicitly considered in the design of metal-arene chiral catalysts.STM images of a single chemisorbed pyrene molecule surrounded by 10 molecules of ethyl formate, one for each aryl CÀH bond, are shown in Figure 1 A,B. These crownlike structures are observed over the entire Pt(111) surface (Figure 1 D). Pyrene is imaged as an oval-shaped protrusion with a long and a short axis, in keeping with its molecular structure. The long axis is collinear with two C À H bonds, whereas the short axis lies between CÀH bonds (Figure 1 C).

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“…Hence, we assume that the strength of the double CH⋅⋅⋅O bond is at least 2–3 kcal mol −1 . This hypothesis is consistent with calculations and experimental data showing that polarized aromatic molecules, such as tetrafluorobenzene, can form relatively strong CH⋅⋅⋅O bonds 20. The observation that the substituted ring of methylnaphthalene is not strongly activated towards CH⋅⋅⋅O bonding is consistent with the fact that all effective modifiers for the Orito reaction contain multiple‐ring aromatic groups.…”

supporting

confidence: 89%

Chemisorption‐Induced Double Hydrogen Bonding, Self‐Assembly, and Stereoselection

Lavoie

¹

,

Mahieu

²

,

McBreen

³

2006

View full text Add to dashboard Cite

By carefully choosing molecular components, it is possible to design supramolecular assemblies on metal surfaces for a variety of applications ranging from templating to asymmetric catalysis. [1][2][3] The choice of molecular building blocks is based on the fundamental chemical concept of functional groups; hydrogen-bond donor-acceptor pairs have proven exceptionally useful for self-assembly. [4][5][6] Hence, it is crucial to recognize that associative chemisorption can generate hydrogen-bond donor functionality in molecules for which hydrogen bonding is negligible in the gas or solution-phase. [7,8] Herein, we report that nonsubstituted arenes form strong C À H···O hydrogen bonds to co-adsorbed esters and ketoesters on Pt(111) surfaces. Scanning tunneling microscopy (STM) imaging is used to isolate well-defined aryl-carbonyl assemblies at 150-300 K and to identify the interaction that binds them as double hydrogen bonding. In this way, chemisorption-activated arenes are found to combine two powerful properties for 2D self-assembly: planarity and double hydrogen bonding. Furthermore, the direct observation of aryl-carbonyl CÀH···O interactions supports a new mechanism for the stereoselective hydrogenation of ketoesters on cinchona-modified platinum. [7] In turn, the observation also suggests that aryl C À H···X bonding, where X is a hydrogen-bond acceptor, should be explicitly considered in the design of metal-arene chiral catalysts.STM images of a single chemisorbed pyrene molecule surrounded by 10 molecules of ethyl formate, one for each aryl CÀH bond, are shown in Figure 1 A,B. These crownlike structures are observed over the entire Pt(111) surface (Figure 1 D). Pyrene is imaged as an oval-shaped protrusion with a long and a short axis, in keeping with its molecular structure. The long axis is collinear with two C À H bonds, whereas the short axis lies between CÀH bonds (Figure 1 C).

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“…However, there has been very limited work to date dealing with clusters in which CH••O HBs play a dominant role. Indeed the first direct evidence of aromatic CH••O HBs in gas phase clusters did not arise until 2005 [56] wherein 1,2,4,5-tetrafluorobenzene served as proton donor to a variety of bases. In terms of calculations, most work has been limited to only small clusters [57][58][59][60][61][62].…”

Section: Introductionmentioning

confidence: 99%

Microsolvation of anions by molecules forming CH··X− hydrogen bonds

Nepal

¹

,

Scheiner

²

2015

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Various anions were surrounded by n molecules of CF 3 H, which was used as a prototype CH donor solvent, and the structures and energies studied by M06-2X calculations with a 6-31+G** basis set. Anions considered included the halides F-, Cl-, Brand I-, as well as those with multiple proton acceptor sites: CN-, NO 3-, HCOO-, CH 3 COO-, HSO 4-, H 2 PO 4-, and anions with higher charges SO 4 2-, HPO 4 2and PO 4 3-. Well structured cages were formed and the average H-bond energy decreases steadily as the number of surrounding solvent molecules rises, even when n exceeds 6 and the CF 3 H molecules begin to interact with one another rather than with the central anion. Total binding energies are very nearly proportional to the magnitude of the negative charge on the anion. The free energy of complexation becomes more negative for larger n initially, but then reaches a minimum and begins to rise for larger values of n.

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A study on aromatic C–H⋯X (X=N, O) hydrogen bonds in 1,2,4,5-tetrafluorobenzene clusters using infrared spectroscopy and ab initio calculations

Cited by 27 publications

References 13 publications

Chemisorption‐Induced Double Hydrogen Bonding, Self‐Assembly, and Stereoselection

Chemisorption‐Induced Double Hydrogen Bonding, Self‐Assembly, and Stereoselection

Chemisorption‐Induced Double Hydrogen Bonding, Self‐Assembly, and Stereoselection

Microsolvation of anions by molecules forming CH··X− hydrogen bonds

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