Effect of Intramolecular Hydrogen Bonds on the Gas-Phase Basicity of Guanidines

2014 ◽  
Vol 67 (7) ◽  
pp. 1056 ◽  
Author(s):  
Zoran Glasovac ◽  
Mirjana Eckert-Maksić
Keyword(s):  
Hydrogen Bond ◽  
Gas Phase ◽  
Model Systems ◽  
Chain Model ◽  
Open Chain ◽  
Independent Variables ◽  
Wide Range ◽  
Intramolecular Hydrogen ◽  
Gas Phase Basicities ◽  
Two Independent Variables

Three series of novel trisubstituted guanidines containing at least one hydrogen bond accepting (HBA) group were modelled using B3LYP/6–311+G(2df,p)//B3LYP/6–31G(d) calculations. Their structure was modified by incorporating a variety of different HBA groups covering a wide range of hydrogen bond strengths. Calculated gas-phase basicities (GBs) ranged from 1035 to 1181 kJ mol–1 depending on the nature of the substituent. To rationalise changes in the GB, a correlation of GB against two independent variables (pKHB and σ4B) was conducted where pKHB served as the descriptor of the hydrogen bond strength and σ4B was introduced to describe changes in the GBs in the open-chain model systems, i.e. in the absence of intramolecular hydrogen bond (IMHB), caused by the electronic effect of the propyl-HBA substituent. A very good correlation of the calculated gas-phase basicities against these two independent variables was established for all three sets of the bases.

scholarly journals HIGH-RESOLUTION GAS PHASE THz SPECTROSCOPY OF THE CATECHOL LOW FREQUENCY MODES INVOLVING AN INTRAMOLECULAR HYDROGEN BOND

2021 ◽  
Author(s):  
Jonas Bruckhuisen ◽  
Arnaud Cuisset ◽  
Marie-Aline Martin-Drumel ◽  
Manuel Goubet ◽  
Thi Tran ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
High Resolution ◽  
Gas Phase ◽  
Intramolecular Hydrogen Bond ◽  
Low Frequency ◽  
Thz Spectroscopy ◽  
Intramolecular Hydrogen

Torsional isomers in methylated aminoethanols - A jet-FT-IR study

2004 ◽  
Vol 82 (6) ◽  
pp. 1006-1012 ◽  
Author(s):  
Yaqian Liu ◽  
Corey A Rice ◽  
Martin A Suhm
Keyword(s):  
Hydrogen Bond ◽  
Gas Phase ◽  
Quantum Chemical ◽  
Supersonic Jet ◽  
Energy Difference ◽  
Ft Ir ◽  
Ir Study ◽  
Intramolecular Hydrogen ◽  
Quantum Chemical Data ◽  
Torsional Isomers

Jet-FT-IR spectra of aminoethanol (AE), N-methylaminoethanol (MAE), and N,N-dimethylaminoethanol (DMAE) are presented and compared to gas-phase and matrix isolation IR, microwave, and quantum chemical data. The intramolecular O-H···N hydrogen bond gives rise to characteristically shifted O-H stretching bands and torsional difference bands in the monomer spectra. It stabilizes one out of 14 diastereomeric monomer conformations of AE and DMAE and two out of 27 diastereomeric MAE conformations. The latter two correspond to torsional or N-inversional isomers, the interconversion of which is hindered by the intramolecular hydrogen bond. Their energy difference is found to be <1.2 kJ/mol. The intermolecular aggregation patterns of the three aminoethanols are quite distinct and non-monotonic, as suggested by their O-H stretching fingerprints.Key words: aminoethanol, IR spectroscopy, conformation, hydrogen bond, supersonic jet.

scholarly journals Attaching onto or Inserting into an Intramolecular Hydrogen Bond: Exploring and Controlling a Chirality-Dependent Dilemma for Alcohols

2021 ◽  
Author(s):  
Manuel Lange ◽  
Elisabeth Sennert ◽  
Martin A. Suhm
Keyword(s):  
Hydrogen Bond ◽  
Benzyl Alcohol ◽  
Intramolecular Hydrogen Bond ◽  
Close Contact ◽  
Supersonic Jet ◽  
Hydroxy Ester ◽  
Model Systems ◽  
Methyl Lactate ◽  
Methyl Glycolate ◽  
Intramolecular Hydrogen

Prereactive complexes in noncovalent organocatalysis are sensitive to the relative chirality of the binding partners and to hydrogen bond isomerism. Both effects are present when a transiently chiral alcohol docks on a chiral &alpha;-hydroxy ester, turning such 1:1 complexes into elementary, non-reactive model systems for chirality induction in the gas phase. With the help of linear infrared and Raman spectroscopy in supersonic jet expansions, conformational preferences are investigated for benzyl alcohol in combination with methyl lactate, also exploring p-chlorination of the alcohol and the achiral homolog methyl glycolate to identify potential London dispersion and chirality effects on the energy sequence. Three of the four combinations prefer barrierless complexation via the hydroxy group of the ester (association). In contrast, the lightest complex shows predominantly insertion into the intramolecular hydrogen bond, like the analogous lactate and glycolate complexes of methanol. The experimental findings are rationalized with computations and a uniform helicality induction in the alcohol by the lactate is predicted, independent on insertion into or association with the internal lactate hydrogen bond. p-Chlorination of benzyl alcohol has a stabilizing effect on association, because the insertion motif prevents a close contact between the chlorine and the hydroxy ester. After simple anharmonicity and substitution corrections, the B3LYP-D3 approach offers a fairly systematic description of the known spectroscopic data on alcohol complexes with &alpha;-hydroxy esters.

A mediated hydrogen bond in an α-hydroxycarboxyl group: X-ray structure of (R,R)-N-methyltartramic acid monohydrate and an ab initio study of model systems

1999 ◽  
Vol 55 (4) ◽  
pp. 617-625 ◽  
Author(s):  
Urszula Rychlewska ◽  
Agnieszka Szarecka ◽  
Jacek Rychlewski ◽  
Rafał Motała
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Gas Phase ◽  
Parent Compound ◽  
Model Systems ◽  
Ab Initio Study ◽  
Liquid Media ◽  
X Ray ◽  
The Stability ◽  
High Polarity

The crystal structure of (R,R)-N-methyltartramic acid monohydrate is presented and compared with that of the parent compound, (R,R)-tartaric acid. Despite some conformational differences between the two molecules the packing is very similar, as it is dictated by the carboxyl rather than the amide function. Particular attention is paid to a mediated three-centre hydrogen bond as one of the packing motifs involving the α-hydroxycarboxyl moiety. The stability and geometry of such structures in the gas phase and in solution are examined via theoretical ab initio methods using the RHF/6-311++G** and RHF/6-311++G**/Onsager models, respectively. Liquid media, in particular those of high polarity, are found to stabilize the structures considerably.

scholarly journals The Effect of Intramolecular Hydrogen Bond Type on the Gas-Phase Deprotonation of ortho-Substituted Benzenesulfonic Acids. A Density Functional Theory Study

Molecules ◽  
2020 ◽  
Vol 25 (24) ◽  
pp. 5806
Author(s):  
Nina I. Giricheva ◽  
Sergey N. Ivanov ◽  
Anastasiya V. Ignatova ◽  
Mikhail S. Fedorov ◽  
Georgiy V. Girichev
Keyword(s):  
Hydrogen Bond ◽  
Gas Phase ◽  
Density Functional ◽  
Structural Features ◽  
Proton Donor ◽  
Comparative Characteristic ◽  
Structural Factors ◽  
Sulfonic Group ◽  
Intramolecular Hydrogen ◽  
Benzenesulfonic Acids

Structural factors have been identified that determine the gas-phase acidity of ortho-substituted benzenesulfonic acid, 2-XC6H4–SO3H, (X = –SO3H, –COOH, –NO2, –SO2F, –C≡N, –NH2, –CH3, –OCH3, –N(CH3)2, –OH). The DFT/B3LYP/cc-pVTZ method was used to perform conformational analysis and study the structural features of the molecular and deprotonated forms of these compounds. It has been shown that many of the conformers may contain anintramolecular hydrogen bond (IHB) between the sulfonic group and the substituent, and the sulfonic group can be an IHB donor or an acceptor. The Gibbs energies of gas-phase deprotonation ΔrG0298 (kJ mol–1) were calculated for all compounds. It has been set that in ortho-substituted benzenesulfonic acids, the formation of various types of IHB is possible, having a significant effect on the ΔrG0298 values of gas-phase deprotonation. If the –SO3H group is the IHB donor, then an ion without an IHB is formed upon deprotonation, and the deprotonation energy increases. If this group is an IHB acceptor, then a significant decrease in ΔrG0298 of gas-phase deprotonation is observed due to an increase in IHB strength and the A− anion additional stabilization. A proton donor ability comparative characteristic of the –SO3H group in the studied ortho-substituted benzenesulfonic acids is given, and the ΔrG0298 energies are compared with the corresponding values of ortho-substituted benzoic acids.

Conformational Terminology for Crystalline Cellulose

1972 ◽  
Vol 50 (6) ◽  
pp. 792-794 ◽  
Author(s):  
P. R. Sundararajan ◽  
R. H. Marchessault
Keyword(s):  
Hydrogen Bond ◽  
Intramolecular Hydrogen Bond ◽  
The Other ◽  
Crystalline Cellulose ◽  
Chain Model ◽  
Glucose Residue ◽  
Straight Chain ◽  
A Value ◽  
Intramolecular Hydrogen ◽  
Mathematical Interpretation

Two different crystalline models of cellulose have received attention from crystallographers: the "straight chain" model of Meyer and Misch and the "bent chain" model of P. H. Hermans. We have examined these models and have given a mathematical interpretation of each in terms of the conformational angles [Formula: see text] and ψ and the glycosidic angle τ. For a given geometry of the glucose residue, the "straight chain" corresponds to a unique value of τ; for a value of τ greater than the unique value, two "bent chains" are possible, one allowing an intramolecular hydrogen bond (O-3 … O-5′) and the other not. It is suggested that the former only be referred to as the Hermans conformation.

Fermi resonance and conformation in glycolaldehyde particles

2004 ◽  
Vol 82 (6) ◽  
pp. 915-924 ◽  
Author(s):  
Martin Jetzki ◽  
David Luckhaus ◽  
Ruth Signorell
Keyword(s):  
Hydrogen Bond ◽  
Fourier Transform ◽  
Gas Phase ◽  
Fermi Resonance ◽  
Dihedral Angles ◽  
Intermolecular Hydrogen Bonds ◽  
Resonance Analysis ◽  
Solid Bulk ◽  
Intramolecular Hydrogen ◽  
Good Agreement

The infrared spectra of gas-phase glycolaldehyde and small glycolaldehyde particles both exhibit a split carbonyl band around 1730 cm–1. Ab initio calculations show that this splitting can be traced back to a Fermi resonance involving the C=O-stretching band and the first overtone of the C–C-stretching band. The analysis of this resonance leads to detailed information about the conformation of glycolaldehyde in the particles. The results can be summarized as follows. (i) In the particles, monomers with OCCO dihedral angles of 0° and CCOH dihedral angles around 50° are strongly preferred. (ii) The intramolecular hydrogen bond observed in the gas phase is partly replaced by intermolecular hydrogen bonds. (iii) The calculated infrared spectrum and the results from the Fermi resonance analysis are in good agreement with the formation of long chains of monomeric glycolaldehyde. This is in contrast to the solid bulk, which consists of chemically bound dimers. Key words: Fermi resonance, conformation, glycolaldehyde particles, hydroxyacetone particles, Fourier transform infrared spectroscopy.

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