Improper hydrogen bonding and motional narrowing in binary mixtures of 2‐ and 3‐bromopyridine in methanol probed by polarized Raman study and DFT calculations

A concentration‐dependent Raman study of the ν(C Br) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH₃OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm⁻¹in the case of 2Br‐p and at ∼618 cm⁻¹ in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman,SERS spectra and computational calculations of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide were recorded and analyzed. A surface‐enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO stretching mode gives the charge transfer interaction through a π‐conjugated path. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported structures. Copyright © 2009 John Wiley & Sons, Ltd.     

NIR‐FT Raman and FT‐IR spectral investigations of the nonlinear optical chromophore p‐bromoacetanilide

Vibrational spectral analysis of the hydrogen‐bonded nonlinear optical (NLO) material p‐bromo acetanilide (PBA) was carried out using NIR‐FT‐Raman and FT‐IR spectroscopy. Ab initio molecular orbital computations were performed at HF/6‐31G (d) level to derive equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The lowering of the imino stretching wavenumbers suggests the existence of strong intermolecular N H···O hydrogen bonding, which was substantiated by the natural bond orbital (NBO) analysis. The vibrational spectra confirm that the charge‐transfer interaction between the  NHCOCH₃ group and—Br through phenyl ring is responsible for simultaneous strong IR and Raman activation of the ring mode 8a. Vibrational analysis indicates that the lowering of stretching wavenumbers of methyl group due to electronic effects simultaneously caused by induction and hyperconjugation is due to the presence of the oxygen atom. The presence of blue‐shifting H‐bonds of CH stretching wavenumbers, simultaneous activation of carbonyl stretching mode, the strong activity of low‐wavenumber H‐bond stretching vibrations and the role of intramolecular charge transfer in making the molecule NLO active have been analyzed on the basis of the vibrational spectral features. Copyright © 2007 John Wiley & Sons, Ltd.     

Spectroscopic and computational studies on self‐assembly complexes of bis(pyrrol‐2‐ ylmethyleneamine) ligands linked by alkyl spacers with Cu(II)

Bis(pyrrol‐2‐ylmethyleneamine) ligands and their mononuclear monomeric and dinuclear dimeric self‐assembly complexes with Cu(II) were investigated by means of IR and Raman spectroscopies and density functional theory. The ground‐state geometries were calculated by using the Becke Lee Yang Parr composite exchange‐correlation functional (B3LYP) and a combined basis set (LanL2DZ for Cu; 6–31G(d) for C, H, N), and they were compared with the single‐crystal X‐ray diffraction (XRD) structures. The DFT‐calculated Cu N bond lengths are generally higher by 0.001–0.040 Å than those determined through XRD. The vibrational spectra were also calculated at the same level of theory for the optimized geometries. The calculated wavenumbers were scaled by a uniform scaling factor and compared with the experimental fundamentals. The predicted spectra are in good agreement with the experimental ones with the deviations generally less than 30 cm⁻¹. In comparison with the spectra of the ligands, the coordination effect shifts the υ(CN) wavenumber by about 50 cm⁻¹ toward a lower value. Because of the weak intermolecular C H···Cu hydrogen bond, the Cu N stretching mode is shifted toward a lower wavenumber. Copyright © 2006 John Wiley & Sons, Ltd.     

Food additives characterization by infrared,Raman, and surface‐enhanced Raman spectroscopies

Fourier‐transform infrared (FT‐IR), Raman (RS), and surface‐enhanced Raman scattering (SERS) spectra of β‐hydroxy‐β‐methylobutanoic acid (HMB), L ‐carnitine, and N‐methylglycocyamine (creatine) have been measured. The SERS spectra have been taken from species adsorbed on a colloidal silver surface. The respective FT‐IR and RS band assignments (solid‐state samples) based on the literature data have been proposed. The strongest absorptions in the FT‐IR spectrum of creatine are observed at 1398, 1615, and 1699 cm⁻¹, which are due to ν_s(COOH) + ν(CN) + δ(CN), ρ_s(NH₂), and ν(C O) modes, respectively, whereas those of L ‐carnitine (at 1396/1586 cm⁻¹ and 1480 cm⁻¹) and HMB (at 1405/1555/1585 cm⁻¹ and 1437–1473 cm⁻¹) are associated with carboxyl and methyl/methylene group vibrations, respectively. On the other hand, the strongest bands in the RS spectrum of HMB observed at 748/1442/1462 cm⁻¹ and 1408 cm⁻¹ are due to methyl/methylene deformations and carboxyl group vibrations, respectively. The strongest Raman band of creatine at 831 cm⁻¹ (ρ_w(R NH₂)) is accompanied by two weaker bands at 1054 and 1397 cm⁻¹ due to ν(CN) + ν(R NH₂) and ν_s(COOH) + ν(CN) + δ(CN) modes, respectively. In the case of L ‐carnitine, its RS spectrum is dominated by bands at 772 and 1461 cm⁻¹ assigned to ρ_r(CH₂) and δ(CH₃), respectively. The analysis of the SERS spectra shows that HMB interacts with the silver surface mainly through the  COO⁻, hydroxyl, and  CH₂ groups, whereas L ‐carnitine binds to the surface via  COO⁻ and  N⁺(CH₃)₃ which is rarely enhanced at pH = 8.3. On the other hand, it seems that creatine binds weakly to the silver surface mainly by  NH₂, and C O from the  COO⁻ group. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman studies of α‐aminophosphinic inhibitors of metalloenzymes

Here, we report the nature of new di‐α‐amino (L¹–L³) and α‐amino‐α‐hydroxyphosphinic (L⁴–L⁶) acids, which are considered potential inhibitors of the aminopeptidase N, adsorbed on a colloidal silver surface by means of surface‐enhanced Raman scattering (SERS) spectroscopy. In order to reveal the adsorption mechanism of these species from their SERS spectra, Fourier‐transform Raman (FT‐RS) spectra of these nonadsorbed molecules were measured. By examining the enhancement, shift in wavenumbers, and changes in breadth of the SERS bands due to the adsorption process, we revealed that the tilted compounds interact with the colloidal silver substrate mainly through the benzene ring, amino group, and phosphinic moiety in the following way. The benzene ring of L² and L³ is ‘standing up’ on the colloidal silver surface, and the C N bond is almost vertical to it, while the tilt angle between the O PO bond and this surface is greater than 45°. On the other hand, for L¹, L⁴, and L⁵, the aromatic ring and C N bond are arranged more or less tilted, and the tilt angle between the O PO bond and the silver substrate is smaller than 45°. The elongation of the bond to the benzene ring, the L⁶ case, produces an almost horizontal orientation of the benzene ring and the O PO bond on the silver nanoparticles. For these ligands, the complement inhibition IC₅₀ tested in vitro using porcine kidney leucine aminopeptidase was correlated mainly with the behavior of the O PO and C CH N fragments on the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

NIR‐FT Raman,FT‐IR and surface‐enhanced Raman scattering spectra,with theoretical simulations on chloramphenicol

Chloramphenicol (CLM), originally derived from the bacterium Streptomyces venezuelae, is an inhibitor of bacterial ribosomal peptidyl transferase activity. The near infrared Fourier transform (NIR‐FT) Raman, surface‐enhanced Raman spectroscopy (SERS) and Fourier transform infrared (FT‐IR) spectral analyses of CLM, a potential antibacterial drug for the treatment of typhoid fever, were carried out along with density functional computations. The vibrational spectral analysis reveals that the CH₂ asymmetric and symmetric stretching modes are shifted to higher wavenumbers than the computed values, owing to the electronic effects resulting from induction of methylene group with the adjacent electronegative atom. The lowering of CO stretching wavenumber is due to the presence of the strong electronegative atom, nitrogen, attached to the carbonyl carbon, causing large degree of molecular π‐electron delocalization and redistribution of electrons, which weakens the CO bond. The absence of a C H stretching vibration and the observed C H out‐of‐plane bending modes suggest that the CLM molecule may be adsorbed in a flat orientation with respect to the silver surface. Copyright © 2008 John Wiley & Sons, Ltd.     

Metal–metal bonding and structures of trinickel and tricobalt dipyridylamido complexes from surface‐enhanced Raman spectra

We recorded surface‐enhanced Raman scattering (SERS) spectra of metal‐string complexes Co₃(dpa)₄ Cl₂ [di(2‐pyridyl)amido (dpa)], Ni₃(dpa)₄ Cl₂ and the oxidized form of the Ni₃ complex to determine their vibrational wavenumbers and to investigate their structures. For SERS measurements these complexes were adsorbed on silver nanoparticles in aqueous solution to eliminate the constraint of a crystal lattice and the complexes remain in thermal equilibrium. From our analysis of the vibrational normal modes we assigned the SERS lines at 242 and 276 cm⁻¹ to Ni₃ and Co₃ symmetric‐stretching modes of the symmetric form. For Co₃ (dpa)₄Cl₂ a Raman line at 383 cm⁻¹ was assigned to the Co Co stretching mode of the unsymmetric form. The wavenumber of the Ni₃ symmetric‐stretching mode of the oxidized form [Ni₃(dpa)₄]³⁺ is 274 cm⁻¹, greater than that for neutral Ni₃(dpa)₄Cl₂, in agreement with a prediction of delocalized molecular‐orbital theory that an electron is removed from an antibonding orbital after oxidation. The experimental data show that the SERS technique serves as an excellent tool to observe the variation of metal–metal bonding during an oxidation or reduction reaction. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and computational study of methyl(2‐methyl‐4,6–dinitrophenylsulfanyl)ethanoate

FT‐IR and FT‐Raman spectra of methyl(2‐methyl‐4,6–dinitrophenylsulfanyl)ethanoate (MDIE) were recorded and analyzed. Surface‐enhanced Raman scattering (SERS) spectra were recorded in silver colloid and silver electrode. The vibrational wavenumbers were computed using HF/6‐31G* and B3LYP/6‐31G* basis. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in infrared and Raman spectroscopies as well as in SERS of the studied molecule. The first hyperpolarizability and infrared intensities are reported. The geometrical parameters of the title compound are in agreement with the reported similar derivatives. The presence of new bands at 1045 and 948 cm⁻¹ in the SERS spectrum in silver electrode is related to the change in orientation of the molecule with respect to the metal surface. In silver colloid SERS spectrum, the methyl group attached to the methoxy carbonyl group is close to the metal surface, whereas on silver electrode the methyl group attached to the phenyl ring is close to the metal surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Adsorption of 4,4′‐thiobisbenzenethiol on silver surfaces: surface‐enhanced Raman scattering study

Adsorption of 4,4′‐thiobisbenzenethiol (4,4′‐TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface‐enhanced Raman scattering (SERS) for the first time, which indicates that 4,4′‐TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H‐atoms of the S H bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4′‐TBBT in the two systems. It is inferred from the SERS signal that the two aromatic rings in 4,4′‐TBBT molecule are parallel to the colloidal silver surface as seen from the disappearance of ν_{C H} band (3054 cm⁻¹), which is a vibrational mode to be used to determine the orientation of a molecule on metals according to the surface selection rule, while on the roughened silver electrode surface they are tilted to the surface as seen from the enhanced signal of ν_{C H}. The orientation of the C‐S bond is tilted with respect to the silver surface in both cases as inferred from the strong enhancement of the ν_{C S}. SERS spectra of 4,4′‐TBBT on the roughened silver electrode with different applied potentials reveal that the enhancement of 4,4′‐TBBT on the roughened silver electrode surface may be related to the chemical mechanism (CM). More importantly, the adsorption of 4,4′‐TBBT on the silver electrode is expected to be useful to covalently adsorb metal nanoparticles through the free S H bond to form two‐ or three‐ dimensional nanostructures. Copyright © 2007 John Wiley & Sons, Ltd.     

Potential dependent thiocyanate adsorption on gold electrodes: a comparison study between SERS and SHINERS

Potential dependent adsorption of target molecules on electrode surface has long been analyzed by several analytical techniques at the electrochemical interfaces. Here, the adsorption of thiocyanate (SCN⁻) on gold electrodes [Au (111) and Au (poly)] is investigated by electrochemical shell isolated nanoparticle‐enhanced Raman spectroscopy (EC‐SHINERS) and surface‐enhanced Raman spectroscopy. Based on the experimental observation, C − N stretching mode of N‐bound SCN⁻ can be observed around 2080 cm⁻¹ throughout the whole potential range. The band corresponding to ν_C−N of S‐bound SCN⁻ appears as a shoulder at more negative potentials, and as a well‐defined band are more positive potentials. However, the overlapped bands provoke a negative shift in the frequency of S‐bound thiocyanate. Therefore, a change in the calculated Stark slope is observed. Interestingly, SHINERS has been employed to demonstrate the thiocyanate orientation and its effect on Raman spectra. Our results widen the opportunities of SHINERS to unravel the potential‐dependent adsorption behavior of target molecules on single‐crystal electrode surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

Density functional theory calculation and vibrational spectral analysis of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one

The Fourier transform infrared (4000–400 cm⁻¹) and Fourier transform Raman (3500–500 cm⁻¹) spectra of 4‐hydroxy‐3‐(3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one (Warfarin) have been measured and calculated. The structure optimization has been made using density functional theory (DFT) calculations. Complete vibrational assignments of the observed spectra have been compared with theoretical wavenumbers. The wavenumber increasing in the methyl group shows the electronic hyperconjugation effect. The natural bond orbital (NBO) analysis reveals the hyperconjugation interaction and the intramolecular hydrogen bonding. The first‐order hyperpolarizability has been calculated. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface enhanced Raman spectroscopic (SERS) behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation

The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)‐2,3‐diphenylpropenoic acid, (E)‐2‐(2‐methoxyphenyl)‐3‐phenylpropenoic acid, (E)‐2,3‐di‐(4‐methoxyphenyl)phenylpropenoic acid and (E)‐2‐(2‐methoxyphenyl)‐3‐(4‐fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO⁻ around 1394 cm⁻¹ and νC―C of the ―C―COO⁻ moiety at 951 cm⁻¹. In these series the plane of the α‐phenyl group (γCH out‐of‐plane vibrations at 850–700 cm⁻¹) is almost parallel to the silver surface, while the β‐phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in‐plane mode) at 1075 cm⁻¹, νCC (ring breathing mode, in‐plane) at 1000 cm⁻¹ and γCCC (out‐of‐plane mode) around 401 cm⁻¹. The other class of propenoic acids (cinnamic acid, (E)‐2‐phenyl‐3‐(4‐methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm⁻¹ in the FT‐Raman spectra of methanolic solutions. Copyright © 2015 John Wiley & Sons, Ltd.     

Adsorbed states of substituted α‐aminophosphinic acids on a silver electrode surface: comparison with a colloidal silver substrate

We investigated the interfacial structures of various aromatic (each compound contains one or two phenyls) di‐α‐amino ( L¹ – L³ ) and α‐amino‐α‐hydroxyphosphinic ( L⁴ – L⁶ ) acids immobilized onto an electrochemically roughened silver electrode surface in an aqueous solution using surface‐enhanced Raman scattering (SERS). These structures were compared to those on a colloidal silver surface to determine the relationship between adsorption strength and geometry. The presence of an enhanced ν_19a ring band in the SERS spectra of L⁶ , L² , and L³ on the electrode indicated that the benzene rings of those molecules interact with the electrode surface through localized CC bond(s). We observed significant band broadening of the benzene ring modes for all α‐hydroxyphosphinic acids on both substrates, except for L¹ deposited onto the electrode surface. This suggests the possibility of direct interaction between the ring and Ag, although the benzene ring–surface π overlap is weaker for the colloidal silver than for the Ag electrode. The downward shift in wavenumber and alternations in the enhancement of a ν₁₂ ring band indicate a general increase of tilt angle on both silver substrates in the order L³ < L⁴ < L⁵ < L⁶ . The altered enhancement of the bands due to the vibrations of the  NH₂ and O PO fragments, a finding observed on both silver substrates, strongly suggests that the groups interact with different strength and geometry with these substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Raman spectra of 3CHBT in unoriented form were recorded at 14 different temperature measurements in the range 25–55 °C, which covers the crystal → nematic (N) phase transition, and the Raman signatures of the phase transition were identified. The wavenumber shifts and linewidth changes of Raman marker bands with varying temperature were determined. The assignments of important vibrational modes of 3CHBT were also made using the experimentally observed Raman and infrared spectra, calculated wavenumbers, and potential energy distribution. The DFT calculations using the B3LYP method employing 6‐31G functional were performed for geometry optimization and vibrational spectra of monomer and dimer of 3CHBT. The analysis of the vibrational bands, especially the variation of their peak position as a function of temperature in two different spectral regions, 1150–1275 cm⁻¹ and 1950–2300 cm⁻¹, is discussed in detail. Both the linewidth and peak position of the ( C H ) in‐plane bending and ν(NCS) modes, which give Raman signatures of the crystal → N phase transition, are discussed in detail. The molecular dynamics of this transition has also been discussed. We propose the co‐existence of two types of dimers, one in parallel and the other in antiparallel arrangement, while going to the nematic phase. The structure of the nematic phase in bulk has also been proposed in terms of these dimers. The red shift of the ν(NCS) band and blue shift of almost all other ring modes show increased intermolecular interaction between the aromatic rings and decreased intermolecular interaction between two  NCS groups in the nematic phase. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of asymmetric wavenumber shift of the Fermi doublet ν1 − 2ν2 in the Raman spectrum of liquid carbon disulfide

The Raman spectra of liquid carbon disulfide (CS₂) diluted with benzene (C₆H₆) have been measured. By changing the CS₂, the concentration, we found an asymmetric wavenumber shift phenomenon. With decreasing concentration of CS₂, the position of the ν₁ (655 cm⁻¹) band remains practically unchanged, and the 2ν₂ (796 cm⁻¹) band shifts toward higher wavenumbers. To interpret this asymmetric wavenumber shift phenomenon of the Fermi doublet ν₁ − 2ν₂ in the Raman spectra satisfactorily, we propose a modified Bertran model. The values of the Fermi resonance (FR) parameters of CS₂ at different concentrations were calculated using the Bertran equations. In addition, we found the fundamental ν₂, which should be independent of the FR interaction, shifted to higher wavenumbers as the concentration decreased. This shift was probably driven by the tuning of the FR. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman and DFT calculations of the salicylanilide derivate 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate

FT‐IR and FT‐Raman spectra of 4‐chloro‐2‐(4‐bromophenylcarbamoyl)phenyl acetate were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighbouring oxygen atom. The simultaneous IR and Raman activations of the CO stretching mode give the charge transfer interaction through a π‐conjugated path. Optimized geometrical parameters of the title compound are in agreement with similar reported structures. From the optimized structure, it is clear that the hydrogen bonding decreases the double bond character of CO bond and increases the double bond character of the C N bonds. The first hyperpolarizability, predicted infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non‐linear optics. The assignments of the normal modes are done by potential energy distribution (PED) calculations. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering of benzenesulfonamide and sulfanilamide adsorbed on silver nanoparticles

The Surface‐enhanced Raman scattering of benzenesulfonamide and sulfanilamide adsorbed on silver sols was studied. On the basis of the noticeable shifts observed for wavenumbers of the ν_s(OSO), ν(CS), and ν(SN) vibrations with respect to the Raman spectra of the solids and the ionic solutions, we conclude that these molecules are adsorbed on silver nanoclusters at pH ≥ 7 with the aminosulfonyl groups partially deprotonated. The benzenesulfonamide links to the metal through the nitrogen atom of the corresponding azanion, while the sulfanilamide interacts in turn through the nitrogen atoms of the –NH₂ and –SO₂NH^– groups in the para‐position. Additionally, it was found that the most enhanced surface‐enhanced Raman scattering bands, especially the 8a;ν_ring mode, are related to the presence of the charge transfer mechanism. Copyright © 2011 John Wiley & Sons, Ltd.     

Why the ΔνCH blue shift is larger in chloral than in dichloroacetyl chloride dimers?

Raman spectra of the Cl₃CCHO/CCl₄ and Cl₃CCHO/C₆D₁₂ binary systems were recorded as a function of the mole fraction. Features originating from self‐aggregates of chloral (trichloroethanal, trichloroacetaldehyde—TCAA) molecules were detected in different spectral regions. The most pronounced changes were observed in the vicinity of the ν(CO) and ν(C H) stretching vibration bands. Using two‐dimensional correlation spectroscopy (2D‐COS), evolving‐factor analysis (EFA) and multivariate curve resolution (MCR), dimer bands were identified, and their positions were determined. The ν(C H) stretching vibration band in dimers was blue‐shifted by nearly 18 cm⁻¹, whereas the ν(CO) dimer band was red‐shifted by more than 5 cm⁻¹. For these bands, the observed shifts were accompanied by an almost twofold change in the bandwidth, from approximately 19 and 6 cm⁻¹ for dilute solutions (x = 0.05) to 36.6 and 11.5 cm⁻¹, respectively, in pure TCAA. The formation of dimers was confirmed by multivariate analysis of the Raman spectra of chloral recorded as a function of temperature. Analogous analysis of dichloroacetyl chloride (DCAC) spectra gave an 8.9 cm⁻¹ blue shift for the ν(C H) vibration band and − 5.5/− 10.1 cm⁻¹ shifts for the ν(CO) stretching vibrations of the two conformers present. To facilitate the interpretation of experimental findings, the optimized geometries and vibrational wavenumbers of the Cl₃CCHO/HCl₂CCClO molecules and (Cl₃CCHO)₂/(HCl₂CCClO)₂ dimers were calculated at the B3LYP/6‐311 + + G(3df,3pd) level. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and DFT calculations of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red‐shift of the NH‐stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO‐stretching mode gives the charge transfer interaction through a π‐conjugated path. Copyright © 2008 John Wiley & Sons, Ltd.