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Spectroscopic and theoretical studies of some N,N-diethyl-2-[(4-substituted)phenylsulfinyl] acetamides
No full textPrevious spectroscopic (IR, 13CNMR,UV and UPS), X-ray studies performed in our laboratories on some β-carbonylsulfoxides XC(O)CH2S(O)R (X=Me, Ar, NR2, OR and SR; R= Me, Ar) [1-5], have shown that their gauche conformer is the most stable, but the cis conformer prevails for the α-sulfinylacetophenones, XC(O)CH2S(O)R [X=Ph; R=Me, Et, iPr, and Ph] [6,7] and X= p-Y-Ph (for Y = OME, Me, H, Cl, and Br; R=Et)] [8], except for R= tBu for the former series, and (Y = CN and NO2; R=Et) for the latter one for which the gauche conformer is the most stable one. The stabilization of the gauche conformers has been attributed to the πCO/σ*C-S and, to a minor extent, to the π*CO/σC-S orbital interactions, while the peculiar stabilization of the cis conformers of the α-alkylsulfinylacetophenones relative to the α-alkyl- and α-aryl-sulfinylacetones has been ascribed to the larger relaxation of the benzene ring π electron charge (due to the πPh-πCO conjugation), which originates stronger intramolecular electrostatic and charge transfer interactions between Cδ+=Oδ- and Sδ+=Oδ- dipoles.
In the MeC(O)X series [9,10] there is a progressive decrease of the experimental carbonyl oxygen lone pair (nO) ionization energy going from ester (Ei=10.45eV) to thioester (Ei=9.64eV) to butanone (Ei=9.46eV), to acetophenone (Ei=9.34eV) and to amide (Ei=9.20eV) for X= OEt, SEt, Et, Ph and NEt2, respectively, which in turn is accompanied by a corresponding increase of the negative charge on the carbonyl oxygen atom in this direction. Therefore it seems reasonable to expect a larger stabilization of the cis conformer of the α-sulfinyl-amides relative to the same conformation of the α-sulfinylacetophenones, due to stronger Cδ+=Oδ-....Sδ+=Oδ- orbital and electrostatic interactions which should operate in the cis conformation of the sulfinyl-amides.
Aiming to throw more light on the nature of the different electronic interactions which may stabilize the cis and gauche conformers of the α-sulfinylamides, this paper reports the IR study of some N,N-diethyl-2-[(4-substituted) phenylsulfinyl] acetamides Et2NC(O)CH2S(O)Ph-Y, bearing in 4- electron-donating, hydrogen and electron-withdrawing substituents i.e. Y= OMe 1,Me 2, H 3,Cl 4, Br 5, NO2 6 (Scheme 1) along with ab initio calculations of 3 and X-ray diffraction analysis of compound 6. These compounds were chosen taking into account that the orbital and Coulombic interactions, which could operate in their cis and gauche conformers, should be affected by changes in the conjugation involving the 4-substituent at the phenylsulfinyl group, and consequently should influence the stabilization of the referred conformers
Comparative spectroscopic and theoretical studies on the conformation of some alpha-diethoxyphosphoryl carbonyl compounds and their alpha-ethylsulfonyl analogues
No full textThe comparative νCO IR analysis between β-carbonylphosphonates [XC(O)CH2 P(O)(OR)2: X=Me 1, Ph 2, OEt 3 , NEt2 4 and SEt 5; R=Et] (series I) and β-carbonylsulfones [XC(O)CH2SO2R: X=Me 6, Ph 7, OEt 8 , NEt2 9 and SEt 10; R=Et] (series II) along with ab initio 6-31G** calculations of 1a and 6a (R=Me) suggest the existence of only a single gauche conformer for I. The negative carbonyl frequency shifts for both series follow approximately the electron-affinities of the π*CO orbital of the parent compounds MeC(O)X 11-15. The less positive asymmetric sulfonyl frequency shifts (ΔνSO2) for II in relation to the phosphoryl frequency shifts (ΔνPO) for I and the larger negative carbonyl frequency shifts for II with respect to the corresponding values for I are in line with the upfield 13C NMR chemical shifts of the carbonyl carbon for II compared to I. These trends agree with the shorter O(SO2)...C(CO)¬ contact in comparison with the O(PO)...C(CO)¬ one and are discussed in terms of Olp * π *CO charge transfer and electrostatic interactions which are stronger for series II than for I, indicating that the sulfonyl oxygen atom is a better electron donor than the phosphoryl oxygen atom. Intrinsic geometrical parameters of O=S-CH2 and O=P-CH2¬ moieties seems to be responsible for this behaviour indicated by X-ray and ab initio calculations of dialkyl methylsulfonylmethanephosphonate MeSO2CH2P(O)(OR)2 (R=Et 18, Me 18a)
Conformational and electronic interaction studies of some p-substituted alpha-bromo-alpha-ethylsulfonylacetophenones
No full textThe preferred conformations of p-substituted α-bromo-α-ethylsulfonylacetophenones Y-PhC(O)CH(Br)SO2Et (Y = OMe 1, Me 2, H 3, Cl 4, Br 5, CN 6 and NO2 7) are determined by νCO IR analysis; HF/ 6-31G** ab initio computations and X-ray diffraction (for 3). In the gas phase compound 3 shows the existence of two stable conformers. The more stable and more polar c1 conformer presents the α-ethylsulfonyl and the α-bromo substituents in syn-periplanar (quasi-cis) and syn-clinal (gauche) geometries, respectively, with respect to the carbonyl group. For the second, less stable and less polar, c2 conformer, both the α substituents assume a syn-clinal (gauche) geometry. The larger stabilisation of the c1 conformer relative to c2, in the gas phase, is attributed to the summing up of the nBr/π*CO and σ C-Br/π*CO hyperconjugative interactions and Oδ-CO...Sδ+SO2, Hδ+CH2[SO2Et]...Oδ-CO. and Oδ-SO2...Cδ+CO orbital and electrostatic interactions, which are stronger for the c1 conformer relative to c2. In solution, only the more polar c1 conformer has been detected, due to its stronger solvation energy relative to that of the c2 conformer. The mean carbonyl frequency shifts (Δν) close to zero, in CCl4, for the single νCO band of the title compounds 1-7 gives further support for its assignment to the c1 conformer as both the quasi-cis conformer of the α-ethylsulfonylacetophenones and the gauche conformer of the α-bromocetophenones present (Δν) values close to zero. X-ray diffraction analysis for 3 indicates that it exists in the solid state in the c1' conformation, which is reasonably close to the c1 one, and it is stabilised intramolecularly by the same interactions responsible for the stabilisation of conformer c1 in the gas phase. Furthermore, these molecules form centro-symmetric dimers in the crystal, which are stabilised through two pairs of intermolecular hydrogen bonds i.e. Hδ+[o-Ph] ...Oδ-SO2 and Hδ+[α-CH] ...Oδ-SO2
Conformational and electronic interaction studies of some alpha-ethylsulfinyl p-substituted acetophenones
No full textThe preferred conformations of the α-ethylsulfinyl p-substituted acetophenones Y_PhC(O)CH2S(O)Et ( Y=OMe 1, Me 2, H 3, Cl 4, Br 5, CN 6, NO2 7) are determined by νCO IR analysis and ab initio HF/6-31G** computations. In solvents of low relative permittivity, carbon tetrachloride and chloroform, the cis2 rotamer prevails over the gauche3 one, excepting for 6 and 7, in chloroform, for which the gauche3 rotamer becomes the most stable. In both solvents the c2/g3 population ratio gradually increases on going from electron-attracting to electron-donating substituents. These trends are discussed in terms of the increasing contribution of the CT and electrostatic and interactions which stabilise the cis2 rotamer along with the simultaneous decreasing contribution of the , orto- and interactions which stabilise the gauche3 rotamer. In the high relative permittivity acetonitrile the gauche3 rotamer becomes the most stable one for the whole series. The good linear correlation of the c2/g3 ratio with both the σp+ substituent constants and the negative cis2 carbonyl frequency shifts (Δνc2), in chloroform indicate that the cis2-gauche3 equilibrium is mainly determined by the interactions which act in the cis2 rotamer, and only to a minor extent by those which operate in the gauche3 rotamer
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Conformational analysis and electronic interactions of some 2- [2′-(4′-sustituted-phenylsulfanyl)-acetyl]-5-substituted furans and 2- [2′-(phenylselanyl)-acetyl]-5-methylfuran
No full textThe conformational equilibrium of 2-[2′-(phenylselanyl)-acetyl]-5-methylfuran (1) and 2-[2′-(4′-sustituted-phenylsulfanyl)-acetyl]-5-substituted furans (2–7) was determined through the infrared (IR) analysis of the carbonyl stretching band (νCO) supported by M06–2X/aug-cc-pVDZ level of theory. Three stable conformations [sc(anti), ac(anti) and sc(syn)] were obtained in vacuum, with the sc(anti) the most stable for compound 1–6 and the ac(anti) for compound 7. The IR spectrain solution of n-C6H14, CCl4, CHCl3, CH2Cl2 and CH3CN show in general νCO doublets for compounds 2–6, with the exception of triplets in n-C6H14 for 2–4 and a symmetrical band in CHCl3 for 1, 3–6 and in CH2Cl2 and CH3CN for 1. The p-nitrophenyl compound 7 is insoluble in n-C6H14 and CCl4 and displays a doublet in all the other polar solvents. The PCM data allow to ascribe the sc(anti) conformer to the lowest frequency more intense νCO IR component and the sc(syn) one to the other doublet component for compounds 1–6, while the intermediary νCO frequency ac(anti) conformer, with negligible population, is assignedto the third triplet component predicted in n-C6H14 for compounds 2–4. Conversely, for compound 7, the more intense and lowest frequency νCOIR component was ascribed to the ac(anti), whereas the highest frequency one to the sum of the sc(anti) and sc(syn) populations. The conformational preferences of compounds 1–7 are governed by a balance between the orbital and the coulombic interactions estimated by means of natural bond orbitals (NBO), quantum theory of atoms in molecules (QTAIM), non covalent interaction (NCI) and short contacts analysis. While NBO delocalization energies indicate the ac(anti) conformer as the most stable for all compounds, NCI analysis reveals in the sc(anti) and sc(syn) conformers of compounds 1–6 an additional intramolecular stabilizing π‧‧‧π stacking interaction between the furyl and phenyl ring, which is counterbalanced in the sc(syn) conformer by the repulsive coulombic short contact between the carbonyl and furyl oxygen atoms. For compound 7, the ac(anti) conformer turns to be the most stable one as the electron withdrawing effect of the nitro substituent on the phenyl ring decreasesthe stabilizing π‧‧‧π stacking on the sc(anti) conformer
Spectroscopic and theoretical studies of some alpha-ethylsulfinyl ortho-substituted acetophenones
No full textThe preferred conformations of the α-ethylsulfinyl ortho-substituted acetophenones X_PhC(O)CH2S(O)Et (X = OMe 1, Me 2, F 3, Cl 4, Br 5, NO2 6) are determined by νCO IR analysis, ab initio HF/6-31G** computations (1-4 and 6) and X-ray diffraction analysis (6). The matching between the IR frequency and intensity of the carbonyl doublet components, in carbon tetrachloride and the results of the calculations indicates that the lower energy component corresponds to the cis2 (anti) conformer for 1, 3-5 and cis2 (syn) for 2. The higher frequency component is related to the gauche3 conformer anti for 3 and syn for 2, 4 and 5, and to the gauche4 (anti) conformer for 1. For 6, gauche conformers correspond to both doublet components. The cis2 conformer population prevails over the gauche one for 1-3 (ca.80%) but not for 4 and 5 (ca.30%). For 6, the lower frequency gauche3 conformer population (85%) is significantly larger than that for the gauche2 one. These trends are discussed in terms of strong stabilising charge transfer and electrostatic interactions between pairs of oppositely charged atoms and their variation with the electronic and steric properties of the X substituent. The X-ray diffraction analysis shows that 6, in the solid state, is in the cis1 conformation which is stabilised through dipole moment coupling and intermolecular hydrogen bonds. In the gas phase and in the crystal, the ortho-nitrophenyl plane is almost perpendicular to the acetyl plane allowing a strong stabilising interaction
Spectroscopic and theoretical studies of some p-substituted alpha-ethylsulfonylacetophenones
No full textThe preferred conformations of p-substituted α-ethylsulfonylacetophenones, Y-PhC(O)CH2SO2Et (Y=OMe 1, Me 2, H 3, F 4, Cl 5, Br 6, CN 7 and NO2 8) are determined by νCO IR analysis, HF/6-31G** computations (1, 3, 5, 7 and 8) and X-ray diffraction for 5 and 7. The match between IR frequencies and intensities of the carbonyl doublet components in carbon tetrachloride (first overtone) and the results of the calculations indicates that the lower frequency component corresponds to the more stable gauche (g) conformer, while the higher frequency component is related to the quasi-cis (q-c) one. The gauche conformer (g) (ca. 85%) prevails over the quasi-cis conformer (q-c) population, and the q-c/g population ratio increases on going from electron-attracting to electron-donating substituents, both in the gas phase and in solution. These trends are discussed in terms of Oδ-(SO2)...Cδ+(CO) charge transfer (CT), Oδ-(CO)...Sδ+(SO2) (Coulombic interaction), Hδ+[CH2(Et)]...Oδ-(CO), Hδ+(2')(o-Ph)...Oδ-(CO) and Hδ+(6')(o-Ph)...Oδ-(SO2) hydrogen bonds and electrostatic interactions, along with the πCO/σ*C-S and π*CO/σC-S orbital interactions, which stabilise the g rotamer. The stabilisation of the q-c rotamer through Oδ-(CO)...Sδ+(SO2) (CT), Hδ+(2')(o-Ph)...Oδ-(CO) and Hδ+[CH2(Et)]...Oδ-(CO) hydrogen bond interactions is counterbalanced by Oδ-(CO)...Oδ-(SO2) electrostatic repulsion, which destabilises significantly this rotamer. The X-ray diffraction analyses show that 5 and 7, in the solid, adopt the cis (c') conformation, which is stabilised through intermolecular hydrogen bonds involving the acidic α-methylene Hδ+(3A), H(3B) and m-phenyl Hδ+(5')[m-Ph] hydrogen atoms and the Oδ-(6), Oδ-(7) sulfonyl and Oδ-(1) carbonyl oxygen atoms
Conformational analysis and electronic interactions of some 2-[2 '-(4 '-substituted-phenylsulfinyl)-acetyl]-5-methylfurans
No full textA conformational study of some 2-[2'-(4'-substituted-phenylsulfinyl)-acetyl]-5-methylfurans 1-4 (OMe1, Me 2, H 3, Cl 4) was performed using IR carbonyl stretching and analysis supported by Natural Bond Orbital (NBO) and Polarisable Continuum Model (PCM) calculations at the B3LYP-D3/aug-cc-pVDZ level, and X-ray diffraction (for 2 and 4). The computational results indicated the existence of four stable conformations with variable degrees of folding (stacking) between the phenyl and the furanyl rings, in the following order of stability: sc(anti)(1)>> ac(syn)>sc(anti)(2) >sc(syn).The PCM data showed that the mean abundance of the most stable lowest frequency sc(anti)(1) conformer in vacuum decreases progressively as the solvent permittivity increases, and, concomitantly, the population of the highest nu(CO) frequency sc(anti)(2) conformer increases in the same direction. Close inspection to the PCM nu(CO) frequencies and populations of the sc(syn) and ac(syn) conformers suggests that their IR lines should be missed due to their low intensities or hidden under the intense lowest nu(CO )component of the sc(anti)(1) conformer. The IR experimental trend observed for the components of the doublet carbonyl band in all solvents just matches the computational results and allows ascribing the most intense lowest nu CO frequency and the least intense highest nu(CO) frequency components in CCl4, to the sc(anti)(1) and sc(anti)(2) conformers, respectively.The appropriate S-(4)(delta+) (center dot center dot center dot) O-(1)(delta-) short contacts stabilise the four conformers to different extents, while the quasi-parallel C delta+ = O delta- and S delta+ = O delta- dipole orientations strongly destabilise electrostatically only the sc(anti)2 conformer. This Repulsive Field Effect is also responsible for the increase in its nu(CO) stretching frequency with respect to the other conformers. The suitable beta and gamma dihedral angles of the anti conformers favour the close proximity of the centroids of the furan and the phenyl rings and the stabilising O-(9)[furan] (center dot center dot center dot) C-(10) [phenyl] short contacts. In contrast, the appropriate geometry adopted by the ac(syn) conformer gives rise to the O-(26)(delta-) (center dot center dot center dot) H-(18)(delta+) short contact and the LPO(26)->sigma*(C6-H18) orbital delocalisation (hydrogen bond), which significantly stabilise this conformer with respect to the sc(syn) form.The sum of the delocalisation energies in the NBO analysis does not match the calculated stability of the four conformers for series 1-4. The closeness of the mean delocalisation energy values found for all the conformers suggests that the computed order of stability is controlled mainly by the relevant short contacts and the coulombic repulsions between the negatively charged carbonyl, sulfinyl and furyl oxygen atoms.In particular, the strong electrostatic short contact O delta-(co) (center dot center dot center dot) O-(SO)(delta-) repulsion and the half as intense O delta-(co)( center dot center dot center dot) O delta-(fur) repulsion destabilise to different extents the sc(anti)(2) and the pair of syn conformers, respectively. Therefore, the calculated order of stability of the four conformers for 1-4 results from the overall balance of the orbital and electrostatic interactions. X-ray single crystal analysis of 2 and 4 revealed that the molecules assume an unfolded (stretched) geometry with a sc(syn) conformation, and that they are stabilised through centrosymmetrical C-H(o-ph) (center dot center dot center dot center dot) O-(co) and C-H(m-ph) (center dot center dot center dot center dot )Cg(1(fur)) interactions (for 2) and C-H(o-ph) O-center dot center dot center dot (co) and C-ph-Cl (center dot center dot center dot) Cg(2(ph)) interactions (for 4). (C) 2019 Elsevier B.V. All rights reserved
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