Charge and energy redistribution in sulfonamides undergoing conformational changes. Hybridization as a controlling influence over conformer stability (original) (raw)
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Journal of Molecular Structure: THEOCHEM, 1989
A comparative ab initio study of amides and sulfonamides has been carried out using minimal, extended and polarization basis sets. Rotational barriers and tautomerism are discussed comparatively. The two main conclusions of this study are the absence in sulfonamides of a conjugation of the type present in planar amides and the relative insensitivity of the total energy to nitrogen hybridization in sulfonamides in contrast with amides.
Arkivoc, 2015
Two conformational diastereoisomers due to the hindered Aryl-NSO 2 rotation were observed by NMR in the model compound N,N'-bis-tosyl-N,N'-dipropargyl-1,4-diamine-2,3-dimethyl benzene 1. X-Ray analysis showed that only the syn conformation is present in the solid state. The conformational preference in solution was evaluated by DFT calculations and experimentally determined by low-temperature NMR experiments. It was found that the anti conformation is the more populated in low-polarity solvents whereas the syn is the favored one in polar solvents.
In this comprehensive study, theoretical investigation was carried out on sulfonamides products with N-alkylation and O-alkylation 1-4 using DFT/B3LYP method with 6-31G (d,p) basis set. The optimized geometrical parameters were calculated by means of density functional theory. Information about size, shape, charge density distribution and site of chemical reactivity of the molecules 1-4 has been obtained by mapping electron density iso-surface with electrostatic potential surface. The lowering in the HOMO and LUMO energy gap for compound 3 explains the eventual charge transfer interactions that take place within the molecule. The chemical reactivity parameters (chemical hardness and softness, electronegativity, chemical potential and electrophilicity index) were discussed clearly and results show that compound 3 is the most reactive. Mulliken population analysis of atomic charges is also computed and interpreted. A detailed molecular picture of the title compounds and there interactions were obtained from NBO analysis. Nonlinear optical NLO behavior of the examined molecule was investigated by the determination of the electric dipole moment µ, the polarizability α and the hyperpolarizability β.
DFT studies of molecular structures conformers and vibrational characteristics of sulfanilamide
Computational and Theoretical Chemistry, 2019
Molecular structures and vibrational parameters for all the four possible conformers of sulfanilamide were studied using Gaussian 09 software and PEDs were calculated using GAR2PED software. MEP and HOMO-LUMO energies were computed and NBO analysis was carried out. Optimized geometries possess C s symmetry. Out of 51 normal modes, 26 modes are conformer sensitive, out of which 2 modes show frequency variation above 75 cm −1 in going from one conformer to another. Out of the 6 internal modes of NH 2 , 4 modes were found at lower frequencies for S-NH 2 group compared to C-NH 2 group, due to presence of intra-molecular O⋯H bonds in the SO 2 (NH 2) group. Strength of nucleophilic attack is stronger with the H atoms of C-NH 2 group compared to the H atoms of the S-NH 2 group. Intra-molecular O⋯H bonds also lead to difference in corresponding geometrical parameters of S-NH 2 and C-NH 2 groups and difference in atomic charges at corresponding sites.
The Shapes of Sulfonamides: A Rotational Spectroscopy Study
Molecules
Benzenesulfonamides are a class of molecules of extreme interest in the biochemical field because many of them are active against a variety of diseases. In this work, the pharmacophoric group benzensulfonamide, its derivatives para-toluensulfonamide and ortho-toluensulfonamide, and the bioactive molecule sulfanilamide, were investigated using rotational spectroscopy to determine their conformations and the influence of different substituents on their structures. For all species, the hyperfine structure due to the 14N atom was analyzed, and this provided crucial information for the unambiguous identification of the observed conformation of all molecules. In addition, for ortho-toluensulfonamide, the vibration–rotation hyperfine structure related to the methyl torsion was analyzed, and the methyl group rotation barrier was determined. For benzensulfonamide, partial rS and r0 structures were established from the experimental rotational constants of the parent and two deuterated isotopi...
Molecular packings and specific-bond patterns in sulfonamides
New Journal of Chemistry, 2014
A novel approach to topological analysis of molecular packings and intermolecular bonding patterns is described and tested on the crystal structures of 1463 sulfonamide derivatives taken from the Cambridge Structural Database, as well as three newly synthesized ones. We have revealed strong correlations between the local and overall topological motifs of hydrogen and halogen specific intermolecular bonds; as a rule, a particular local connection type of the molecules provides only one most preferred pattern of intermolecular bonds and vice versa. Molecular packings are found to be almost independent of the existence or absence of specific bonds and in more than 1/3 of cases they obey Kitaigorodskii's model of close packing. The peculiar shapes of the sulfonamide molecules in some cases give rise to a special 'butterfly' packing that is topologically less dense than close packings. The correlations found can be used to predict the main peculiarities of molecular crystals with a prospective expert system. † Electronic supplementary information (ESI) available: Crystallographic data for compounds I-III. Tables S1-S10 contain distributions of connection types and the overall topological motifs in molecular packings and specific-bonding patterns in 1463 sulfonamide derivatives. CCDC 989765-989767. For ESI and crystallographic data in CIF or other electronic format see
Effect of a Rigid Sulfonamide Bond on Molecular Folding: A Case Study
Crystal Growth & Design, 2015
A disulfonamide compound with bulky aromatic side chains was prepared and its properties as a potential building block for foldamers evaluated. Two different solvate crystal forms of the compound were identified and compared to the structures of an analogous oligoamide and related disulfonamides. The disulfonamide is unfolded in one of the solvates, whereas in the other one, a loosely folded conformer stabilized by an intramolecular hydrogen bond is found. Density functional calculations indicated that the loosely folded conformer is slightly more stable than its unfolded isomer. The calculations also identified a third, more tightly folded and more extensively hydrogen bonded conformer that is even lower in energy.
A molecular mechanics valence force field for sulfonamides derived by ab initio methods
The Journal of Physical Chemistry, 1991
The comparison of the SiH3 and Si(CH3), parameters is also understood on the basis of similar arguments. The inductive effect of CH3 vs H facilitates transfer. The partial positive charge resulting from more extensive transfer in (CH3),Si is localized mainly on silicon, leading to a 10% increase in the E number over that of SiH,. The inductive effect of the CH, group compared to H raises the energy of the silicon u bonding molecular orbital used to form SiX , leading to a poorer energy match between silicon and X and a smaller C number. The influence of ancillary groups (L) in general on the L,M-X bond energy is an important concept to understand. Patterns in substituent effects on E, C, and Tare beginning to emerge from the limited data available. In the case of carbon, substituting methyl for the three hydrogens of the methyl animer leading to tert-butyl results in an increase in E of 0.4 (-IO%), a decrease in C of 1.5 (-1 1 a), and an increase in Tof 1.5 (-90%). These changes pretty much compensate one another, leading to minor differences in the C-X bond energies for CH, and (CH3),C. The increased transfer in the (CH3),C catimer suggests that the CH3 substituent facilitates transfer better than hydrogen by stabilizing the positive charge on carbon probably by inductive transfer in the u system. However, the electron density that is transferred comes largely from the tertiary carbon, with the E number for tert-butyl being larger than for CH3 even though tert-butyl is larger. Poorer covalency and increased ionicity in the C-X bond and in some cases steric effects will stabilize the formation of the carbonium ion of (CH3),C over CH,, with some charge delocalization onto the CH3 of C(CH)3 contributing to the stability. The effect of substituting CH3 for H on silicon changes E and C in the same direction as that observed for carbon. Comparing (CH3),Si to H3Si, the E term increases by 0.8 (IO%), the C term decreases by 0.4 (4%), and Tincreases by 1.4 (21%). The above arguments for carbon explain these trends. A small decrease in covalency and the more than compensating increases in the contributions from E and T cause all (CH,),Si-X bond energies to be stronger and the bond more ionic than H,Si-X. The bond energies in the two systems will be closest for those animers with a small T and a large C/E ratio. With the ECT approach, we are now in a position to predict bond energies for CH,-X, CIHS-X, t-C,H,-X, (CH3)$i-X, and SiH,-X with over 20 different X animers to about 1.5 kcal mol-'. Steric effects in the tert-butyl system and *-bond stabilization with first-row animers in the silicon system will lead to contributions other than "normal" u-bond strengths and cause deviations in some of the calculated and experimental values. The deviation between the predicted a-bond enthalpy and that measured provides a unique, quantitative measure of the magnitude of steric effects or *-bond stabilization (i.e., *-bond strength and the synergistic increase in the u-bond strength). Calculations The least-squares data fits carried out in this work involved substituting enthalpies or in one instance V, values into eq 1 to produce a series of simultaneous equations. Reported values for the animer are also substituted into these equations, leading to three unknowns in each equation. A least-squares minimization routine is used to solve the series of equations for three unknowns. The parameters used for C1, Br, and I are those reported.s Better bond energies for CH,-X and C2HS-X and bond energies for some organometallic halidesS were used to refine the parameters reported in the initial publication^.^^^ Registry No. C, 7440-44-0; Si, 7440-21-3.
A database study of the bonding and conformation of bis-sulfonylamide/-imide moieties
Acta Crystallographica Section B Structural Science, 1996
The bonding and conformational characteristics of bissulfonylamides and analogous imides are compared. Structures (44 altogether) containing R--SO2--NQ--SO2--R' units were retrieved from the Cambridge Structural Database. They are either neutral (Q-H, alkyl or aryl groups, hereto atoms such as O and S) or charged (Q = e-) and bearing the functions R, R' =Me, Et or Ph, respectively. The principal conformations of the --SO 2-NQ--SO 2-bridge (open versus folded) are represented by sodium dibenzenesulfonamide (BSULFA) and dibenzenesulfonimide (NABSUF). In addition to the compounds possessing Q= alkyl or aryl functions, complexes with N-metal bonds could clearly be distinguished. The dominant forms of S vl --X (X = O, N C) bonds are characterized and correlated with the bond angles formed around the S atoms. The marked difference between the archetypes of the S--N bonds (i.e. nitrogen charged or neutral) indicated that the interdependence of the S--X bonds, i.e. the size and the shape of the SvI[o,O',N,C] tetrahedra, are principally governed by the environment of the N atoms. The conformation symmetry and dissymmetry of the charged and neutral --SO2--NQ--SO 2-moieties are described in terms of the internal rotations about the bonds in the R--S--N--S--R' fragment.