Electrostatic Effects in Ionization Equilibria: An AM1 Study of Reversed Substituent Effect in 5-Fluorobicyclo[3.3.3]undecane-1-carboxylic Acid

1994 ◽  
Vol 59 (7) ◽  
pp. 1467-1471
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm
Keyword(s):  
Carboxylic Acid ◽  
Proton Transfer ◽  
Substituent Effect ◽  
Am1 Method ◽  
Electrostatic Effects ◽  
Ionization Equilibria ◽  
Electrostatic Theory

Relative proton transfer enthalpies δ ∆H0 of sp and ap conformers of 5-fluorobicyclo[3.3.3]undecane-1-carboxylic acid have been calculated by the AM1 method and the results were compared with the prediction of the electrostatic theory. It is shown that the great reversed substituent effect in the sp conformer (δ ∆H0 = 32.1 kJ mol-1) is substantially overestimated largely due to sterical Baeyer strain and non-bonded interactions.

Ionic dimerisation of trifluoropropenenitrile and its addition reactions with methyl trifluoropropenoate

1980 ◽  
Vol 45 (2) ◽  
pp. 406-414 ◽  
Author(s):  
Jiří Svoboda ◽  
Oldřich Paleta ◽  
Václav Dědek
Keyword(s):  
Reaction Mechanism ◽  
Proton Transfer ◽  
Substituent Effect ◽  
Solvent Molecule ◽  
Addition Product ◽  
Potassium Fluoride ◽  
Relative Reactivity ◽  
Addition Reactions ◽  
Tertiary Amines ◽  
Optimum Conditions

Dimerisation of trifluoropropenenitrile (I) in the presence of potassium fluoride and tertiary amines afforded a mixture of stereoisomeric perfluoro-4-methyl-pentenedinitriles (II), higher-boiling compounds, and 2,3,3,3-tetrafluoropropanenitrile (III) which arises by proton transfer from the solvent molecule. Under optimum conditions, product II was obtained in about 50% yield. Reaction of the nitrile I with methyl trifluoropropenoate (IV) gave, besides the dimers II and V, the product of addition of the nitrile I to the propenoate, IV, i.e. methyl 4-cyanoperfluoro-2-pentenoate (VI), and the addition product of the propenoate IV to the nitrile I, i.e. methyl 4-cyanoperfluoro-2-methyl-3-butenoate (VII). The relative reactivity if I and IV is discussed. The ratio of stereoisomers in II, V, VI and VII indicates that the magnitude of the steric substituent effect, operating in the reaction mechanism, decreases in the order -CFCF3.(COOCH3) > -CFCF3(CN) > -COOCH3 > -CN.

Isolated complexes of the amino acid arginine with polyether and polyamine macrocycles, the role of proton transfer

2017 ◽  
Vol 19 (46) ◽  
pp. 31345-31351 ◽  
Author(s):  
Juan Ramón Avilés-Moreno ◽  
Giel Berden ◽  
Jos Oomens ◽  
Bruno Martínez-Haya
Keyword(s):  
Amino Acid ◽  
Carboxylic Acid ◽  
Proton Transfer ◽  
Acid Group ◽  
Side Group ◽  
Carboxylic Acid Group

Protonated arginine interacts with 12-crown-4 through the guanidinium side group. In the complex with the N-substituted analog cyclen, the dominant conformation is the result of the proton transfer from the carboxylic acid group of the amino acid to the macrocycle.

A New Supramolecular Synthon Using N-Methylaniline. The Crystal Structure of the 1 : 1 Adduct of N-Methylaniline with 5-Nitrofuran-2-carboxylic Acid

1998 ◽  
Vol 51 (9) ◽  
pp. 867 ◽  
Author(s):  
Daniel E. Lynch ◽  
Lisa C. Thomas ◽  
Graham Smith ◽  
Karl A. Byriel ◽  
Colin H. L. Kennard
Keyword(s):  
Crystal Structure ◽  
Carboxylic Acid ◽  
Proton Transfer ◽  
Single Crystal ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Supramolecular Synthon ◽  
X Ray ◽  
C 23 ◽  
A Cell

The crystal structure of the 1 : 1 adduct of N-methylaniline with 5-nitrofuran-2-carboxylic acid has been determined by single-crystal X-ray diffraction. Crystals are monoclinic, space group P21/c with Z 4 in a cell of dimensions a 8·467(5), b 6·106(2), c 23·95(1) Å, β 94·48(3)°. The molecules associate in a tetrameric, proton-transfer formation which has potential as a new supramolecular synthon.

Excited state intramolecular proton transfer in 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole: effects of solvents and pH

2000 ◽  
Vol 78 (2) ◽  
pp. 191-205 ◽  
Author(s):  
Somes K Das ◽  
G Krishnamoorthy ◽  
Sneh K Dogra
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Radiative Decay ◽  
Intramolecular Proton Transfer ◽  
Normal Band ◽  
Am1 Method ◽  
Excitation Spectra ◽  
Fluorescence Excitation ◽  
Protic Solvents ◽  
Fluorescence Excitation Spectra

The solvent dependent study of absorption, fluorescence, and fluorescence excitation spectra of 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole (HPNI) have indicated the presence of different rotamers and tautomers in the So and S1 states. Similarity of the absorption and fluorescence spectra of HPNI in protic solvents with those of 2-(2'-methoxyphenyl)-1H-naphth-[2,3-d]-imidazole (MPNI) suggests that the normal emission is observed from the rotamers 2 and 4, whereas the tautomer emission is observed from the tautomer 3, formed by the excited state intramolecular proton transfer (ESIPT) in the rotamer 1 (Scheme 1). Ground state geometries of rotamers 1, 2, and the tautomer 3 were optimized using AM1 method. The results show that the rotamer 2 is the most stable and its stability further increases in polar and protic solvents due to the dipolar solvation interaction. The increase in the fluorescence quantum yield of the normal band when methanol or water is added to dioxane is due to: (i) the formation of rotamer 4, where ESIPT is not possible and (ii) the decrease in the rate of non-radiative decay process. Very large red shifted fluorescence bands of the monocations of HPNI and MPNI in different solvents have been assigned to the charge transfer band.Key words: 2-(2'-hydroxyphenyl)-1H-naphth-[2,3-d]-imidazole, ESIPT, prototropic reactions, fluorescence, 2-(2'-methoxyphenyl)-1H-naphth-[2,3-d]-imidazole.

Solvent-mediated pseudo-quadruple hydrogen-bond motifs in three lamotrigine–carboxylic acid complexes

2013 ◽  
Vol 69 (10) ◽  
pp. 1164-1169 ◽  
Author(s):  
Balasubramanian Sridhar ◽  
Jagadeesh Babu Nanubolu ◽  
Krishnan Ravikumar
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Proton Transfer ◽  
Antiepileptic Drug ◽  
Carboxylic Acids ◽  
Solvent Interactions ◽  
Partial Transfer ◽  
Quadruple Hydrogen Bonding ◽  
Quadruple Hydrogen Bond

Lamotrigine, an antiepileptic drug, has been complexed with three aromatic carboxylic acids. All three compounds crystallize with the inclusion ofN,N-dimethylformamide (DMF) solvent,viz.lamotriginium [3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazin-2-ium] 4-iodobenzoateN,N-dimethylformamide monosolvate, C9H8Cl2N5+·C7H4IO2−·C3H7NO, (I), lamotriginium 4-methylbenzoateN,N-dimethylformamide monosolvate, C9H7Cl2N5+·C8H8O2−·C3H7NO, (II), and lamotriginium 3,5-dinitro-2-hydroxybenzoateN,N-dimethylformamide monosolvate, C9H8Cl2N5+·C7H3N2O7−·C3H7NO, (III). In all three structures, proton transfer takes place from the acid to the lamotrigine molecule. However, in (I) and (II), the acidic H atom is disordered over two sites and there is only partial transfer of the H atom from O to N. In (III), the corresponding H atom is ordered and complete proton transfer has occurred. Lamotrigine–lamotrigine, lamotrigine–acid and lamotrigine–solvent interactions are observed in all three structures and they thereby exhibit isostructurality. The DMF solvent extends the lamotrigine–lamotrigine dimers into a pseudo-quadruple hydrogen-bonding motif.

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