IR/Raman spectroscopy and DFT calculations of cyclic di‐amino acid peptides. Part III: comparison of solid state and solution structures of cyclo(L‐Ser‐L‐Ser)

B3‐LYP/cc‐pVDZ calculations of the gas‐phase structure and vibrational spectra of the isolated molecule cyclo(L ‐Ser‐L ‐Ser), a cyclic di‐amino acid peptide (CDAP), were carried out by assuming C₂ symmetry. It is predicted that the minimum‐energy structure is a boat conformation for the diketopiperazine (DKP) ring with both L ‐seryl side chains being folded slightly above the ring. An additional structure of higher energy (15.16 kJ mol⁻¹) has been calculated for a DKP ring with a planar geometry, although in this case two fundamental vibrations have been calculated with imaginary wavenumbers. The reported X‐ray crystallographic structure of cyclo(L ‐Ser‐L ‐Ser), shows that the DKP ring displays a near‐planar conformation, with both the two L ‐seryl side chains being folded above the ring. It is hypothesized that the crystal packing forces constrain the DKP ring in a planar conformation and it is probable that the lower energy boat conformation may prevail in the aqueous environment. Raman scattering and Fourier‐transform infrared (FT‐IR) spectra of solid state and aqueous solution samples of cyclo(L ‐Ser‐L ‐Ser) are reported and discussed. Vibrational band assignments have been made on the basis of comparisons with the calculated vibrational spectra and band wavenumber shifts upon deuteration of labile protons. The experimental Raman and IR results for solid‐state samples show characteristic amide I vibrations which are split (Raman: 1661 and 1687 cm⁻¹, IR: 1666 and 1680 cm⁻¹), possibly due to interactions between molecules in a crystallographic unit cell. The cis amide I band is differentiated by its deuterium shift of ∼30 cm⁻¹, which is larger than that previously reported for trans amide I deuterium shifts. A cis amide II mode has been assigned to a Raman band located at 1520 cm⁻¹. The occurrence of this cis amide II mode at a wavenumber above 1500 cm⁻¹ concurs with results of previously examined CDAP molecules with low molecular weight substituents on the C^α atoms, and is also indicative of a relatively unstrained DKP ring. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies of the structure of di‐amino acid peptides. Part II: cyclo(L‐Asp‐L‐Asp) in the solid state and in aqueous solution

Solid‐state protonated and N,O‐deuterated Fourier transform infrared (IR) and Raman scattering spectra together with the protonated and deuterated Raman spectra in aqueous solution of the cyclic di‐amino acid peptide cyclo(L ‐Asp‐L ‐Asp) are reported. Vibrational band assignments have been made on the basis of comparisons with previously cited literature values for diketopiperazine (DKP) derivatives and normal coordinate analyses for both the protonated and deuterated species based upon DFT calculations at the B3‐LYP/cc‐pVDZ level of the isolated molecule in the gas phase. The calculated minimum energy structure for cyclo(L ‐Asp‐L ‐Asp), assuming C₂ symmetry, predicts a boat conformation for the DKP ring with both the two L ‐aspartyl side chains being folded slightly above the ring. The CO stretching vibrations have been assigned for the side‐chain carboxylic acid group (e.g. at 1693 and 1670 cm⁻¹ in the Raman spectrum) and the cis amide I bands (e.g. at 1660 cm⁻¹ in the Raman spectrum). The presence of two bands for the carboxylic acid CO stretching modes in the solid‐state Raman spectrum can be accounted for by factor group splitting of the two nonequivalent molecules in a crystallographic unit cell. The cis amide II band is observed at 1489 cm⁻¹ in the solid‐state Raman spectrum, which is in agreement with results for cyclic di‐amino acid peptide molecules examined previously in the solid state, where the DKP ring adopts a boat conformation. Additionally, it also appears that as the molecular mass of the substituent on the C^α atom is increased, the amide II band wavenumber decreases to below 1500 cm⁻¹; this may be a consequence of increased strain on the DKP ring. The cis amide II Raman band is characterized by its relatively small deuterium shift (29 cm⁻¹), which indicates that this band has a smaller N H bending contribution than the trans amide II vibrational band observed for linear peptides. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectra and crystal structure of the di‐amino acid peptide cyclo(L‐Met‐L‐Met): comparison of experimental data and DFT calculations

Experimental Raman and FT‐IR spectra of solid‐state non‐deuterated and N‐deuterated samples of cyclo(L ‐Met‐L ‐Met) are reported and discussed. The Raman and FT‐IR results show characteristic amide I vibrations (Raman: 1649 cm⁻¹, infrared: 1675 cm⁻¹) for molecules exhibiting a cis amide conformation. A Raman band, assigned to the cis amide II vibrational mode, is observed at ∼1493 cm⁻¹ but no IR band is observed in this region. Cyclo(L ‐Met‐L ‐Met) crystallises in the triclinic space group P1 with one molecule per unit cell. The overall shape of the diketopiperazine (DKP) ring displays a (slightly distorted) boat conformation. The crystal packing employs two strong hydrogen bonds, which traverse the entire crystal via translational repeats. B3‐LYP/cc‐pVDZ calculations of the structure of the molecule predict a boat conformation for the DKP ring, in agreement with the experimentally determined X‐ray structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di‐amino acid peptide cyclo(L‐Glu‐L‐Glu)

Cyclo(L ‐Glu‐L ‐Glu) has been crystallised in two different polymorphic forms. Both polymorphs are monoclinic, but form 1 is in space group P2₁ and form 2 is in space group C2. Raman scattering and FT‐IR spectroscopic studies have been conducted for the N,O‐protonated and deuterated derivatives. Raman spectra of orientated single crystals, solid‐state and aqueous solution samples have also been recorded. The different hydrogen‐bonding patterns for the two polymorphs have the greatest effect on vibrational modes with N H and CO stretching character. DFT (B3‐LYP/cc‐pVDZ) calculations of the isolated cyclo(L ‐Glu‐L ‐Glu) molecule predict that the minimum energy structure, assuming C₂ symmetry, has a boat conformation for the diketopiperazine ring with the two L ‐Glu side chains being folded above the ring. The calculated geometry is in good agreement with the X‐ray crystallographic structures for both polymorphs. Normal coordinate analysis has facilitated the band assignments for the experimental vibrational spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison of adsorption mechanism on colloidal silver surface of alafosfalin and its analogs

This study reports the Raman (FT‐RS) and absorption infrared (FT‐IR) spectra, based on calculated wavenumbers and normal modes of vibrations, of the following compounds: L ‐Ala‐L ‐NH‐CH(Me)‐PO₃H₂ (alafosfalin, A1), L ‐Ala‐D ‐NH‐CH(Me)‐PO₃H₂ (A2), L ‐Ala‐L ‐NH‐CH(Et)‐PO₃H₂ (A3), D ,L ‐Ala‐D,L ‐NH‐CH(Et)‐PO₃H₂ (A4), L ‐Ala‐D ‐NH‐CH(iPr)‐PO₃H₂ (A5), L ‐Ala‐D,L ‐NH‐CH(iPr)‐PO₃H₂ (A6), L ‐Ala‐D,L ‐NH‐CH(tBu)‐PO₃H₂ (A7), L ‐Ala‐D,L ‐NH‐CH(iBu)‐PO₃H₂ (A8), L ‐Ala‐D,L ‐NH‐CH(cBu)‐PO₃H₂ (A9), L ‐Ala‐D,L ‐NH‐CH(nPA)‐PO₃H₂ (A10), β‐Ala‐D ‐NH‐CH(Me)‐PO₃H₂ (A11), and D,L ‐Ala‐NH‐C(Me,Me)‐PO₃H₂ (A12). The equilibrium geometries and vibrational wavenumbers are calculated using density functional theory (DFT) at the B3LYP; 6–31 + + G** level of theory using Gaussian'03, GaussSum 0.8, and GAR2PED software. We briefly compare and analyze the experimental and calculated vibrational wavenumbers in the range of 3600–400 cm⁻¹. In addition, Raman wavenumbers are compared to those from surface‐enhanced Raman scattering (SERS) for the phosphonodipeptides of alanine (Ala) adsorbed on a colloidal silver surface. The geometry of these molecules etched on the silver surface is deduce from the observed changes in both the intensity and breadth of Raman bands in the spectra of the bound vs free species. For example, A7, A8, A1, A3, and A4 appear to adsorb onto the colloidal silver particles mainly through the phosphonate terminus, and for A3 and A4, through the  C‐NH₂ and  CONH fragments. The most dominant SERS bands of A5, A6, A9, A10, and A11 are due to the amide bond vibrations, as well as to the vibrations of the  C‐NH₂ group (A9 and A10) and the C C group (A6 and A11). The differences recorded for the A5, A6, A9, A10, and A11 and those of A2 and A12 are due to interactions between the amine and methyl groups with the silver surface, and they reflect vibrational characteristic of these groups. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman scattering of L‐tryptophan enhanced by surface plasmon of silver nanoparticles: vibrational assignment and structural determination

Vibrational bands of L ‐tryptophan which was adsorbed on Ag nanoparticles (∼10 nm in diameter) have been investigated in the spectral range of 200–1700 cm⁻¹ using surface‐enhanced Raman scattering (SERS) spectroscopy. Compared with the normal Raman scattering (NRS) of L ‐tryptophan in either 0.5 M aqueous solution (NRS‐AS) or solid powder (NRS‐SP), the intensified signals by SERS have made the SERS investigation at a lower molecular concentration (5 × 10⁻⁴ M ) possible. Ab initio calculations at the B3LYP/6‐311G level have been carried out to predict the optimal structure and vibrational wavenumbers for the zwitterionic form of L ‐tryptophan. Facilitated with the theoretical prediction, the observed vibrational modes of L ‐tryptophan in the NRS‐AS, NRS‐SP, and SERS spectra have been analyzed. In the spectroscopic observations, there are no significant changes for the vibrational bands of the indole ring in either NRS‐AS, NRS‐SP, or SERS. In contrast, spectral intensities involving the vibrations of carboxylate and amino groups are weak in NRS‐AS and NRS‐SP, but strong in SERS. The intensity enhancement in the SERS spectrum can reach 10³–10⁴‐fold magnification. On the basis of spectroscopic analysis, the carboxylate and amino groups of L ‐tryptophan are determined to be the preferential terminal groups to attach onto the surfaces of Ag nanoparticles in the SERS measurement. Copyright © 2008 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and DFT calculations of di‐amino acid peptides: α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu in the solid state

Experimental vibrational spectroscopic studies and density functional theory (DFT) calculations of the di‐amino acid peptide derivatives α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu have been undertaken. Raman and infrared spectra have been recorded for samples in the solid state. DFT simulations were conducted using the B3‐LYP correlation functional and the cc‐pVDZ basis set to determine energy minimized/geometry optimized structures (based on a single isolated molecule in the gaseous state). Normal coordinate calculations have provided vibrational assignments for fundamental modes, including their potential energy distributions. Significant differences are observed between α‐ and β‐N‐acetyl‐L‐Asp‐L‐Glu both in the computed structures and in the vibrational spectra. The combination of experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of di‐amino acid peptide derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of an aliphatic spacer group on the adsorption mechanism on the colloidal silver surface of L‐proline phosphonodipeptides

A comparative study of molecular structures of five L ‐proline (L ‐Pro) phosphonodipeptides: L ‐Pro‐NH‐C(Me,Me)‐PO₃H₂ (P1), L ‐Pro‐NH‐C(Me,iPr)‐PO₃H₂ (P2), L ‐Pro‐L ‐NH‐CH(iBu)‐PO₃H₂ (P3), L ‐Pro‐L ‐NH‐CH(PA)‐PO₃H₂ (P4) and L ‐Pro‐L ‐NH‐CH(BA)‐PO₃H₂ (P5) has been carried out using Raman and absorption infrared techniques of molecular spectroscopy. The interpretation of the obtained spectra has been supported by density functional theory calculations (DFT) at the B3LYP; 6–31 + + G** level using Gaussian 2003 software. The surface‐enhanced Raman scattering (SERS) on Ag‐sol in aqueous solutions of these phosphonopeptides has also been investigated. The surface geometry of these molecules on a silver colloidal surface has been determined by observing the position and relative intensity changes of the Pro ring, amide, phosphonate and so‐called spacer (−R) groups vibrations of the enhanced bands in their SERS spectra. Results show that P4 and P5 adsorb onto the silver as anionic molecules mainly via the amide bond (∼1630, ∼1533, ∼1248, ∼800 and ∼565 cm⁻¹), Pro ring (∼956, ∼907 and ∼876 cm⁻¹) and carboxylate group (∼1395 and ∼909 cm⁻¹). Coadsorption of the imine nitrogen atom and PO group with the silver surface, possibly by formation of a weaker interaction with the metal, is also suggested by the enhancement of the bands at 1158 and 1248 cm⁻¹. P1, P2 and P3 show two orientations of their main chain on the silver surface resulting from different interactions of the  C CH₃,  NH and  CONH fragments with this surface. Bonding to the Ag surface occurs mainly through the imino atom (1166 cm⁻¹) for P2, while for P1 and P3 it occurs via the methyl group(s) (1194–1208 cm⁻¹). The amide group functionality (CONH) is practically not involved in the adsorption process for P1 and P2, whereas the C_s P bonds do assist in the adsorption. Copyright © 2008 John Wiley & Sons, Ltd.     

High‐pressure Raman spectroscopy of nanoparticle polyacetylene in a poly(vinyl‐butyral) matrix

The pressure‐induced Raman shifts of six vibrational bands of 20% and 50% trans‐polyacetylene nanoparticles in poly(vinyl‐butyral) matrix films (NPA/PVB) were studied from 0 to 45 kbar using a diamond anvil cell (DAC). The Raman shifts did not depend on the thickness of the two samples studied. Two of the vibrational bands displayed peak positions that depended on the isomeric compositions, with the 20% trans‐NPA/PVB bands being slightly blue‐shifted relative to the 50% trans‐NPA/PVB bands over the 45 kbar pressure range. The Raman bands of NPA/PVB associated with the trans form initially exhibited a relatively large shift at low pressures (P < 10 kbar) along with a drastic change in their band profile. In order to investigate the relative shielding of the vibrational modes studied, a Grüneisen analysis of the pressure‐induced shifts was conducted by estimating the parameters of the Murnaghan equation of state for solid polyacetylene (PA). Four of the six vibrational modes were found to be sensitive to compression of the interchain void space, while the other two modes were insensitive, indicating that they are relatively shielded from the compression of the sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman and ab initio study of the conformational isomerism in the 1‐ethyl‐3‐methyl‐imidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

The calculated and experimental Raman spectra of the (EMI⁺)TFSI⁻ ionic liquid, where EMI⁺ is the 1‐ethyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI⁺ and TFSI⁻ conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non‐planar (np) EMI⁺ conformers are identified using the reference (EMI⁺)Br⁻ salt. The anion conformer of C₂ symmetry is confirmed to be more stable than the cis (C₁) one by 4.5 ± 0.2 kJ mol⁻¹. At room temperature, the population of trans (C₂) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C₂ anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C₁ anion conformers and of np cation conformers. Copyright © 2006 John Wiley & Sons, Ltd.     

Vibrational characterization of L‐valine phosphonate dipeptides: FT‐IR,FT‐RS,and SERS spectroscopy studies and DFT calculations

Four L ‐valine (L ‐Val) phosphonate dipeptides that are potent inhibitors of zinc metalloproteases, namely, L ‐Val‐C(Me)₂‐PO₃H₂ (V1), L ‐Val‐CH(iP)‐PO₃H₂ (V2), L ‐Val‐CH(iB)‐PO₃H₂ (V3), and L ‐Val‐C(Me)(iP)‐PO₃H₂ (V4), are studied by Fourier‐transform infrared (FT‐IR) spectroscopy, Fourier‐transform Raman spectroscopy (FT‐RS), and surface‐enhanced Raman scattering (SERS). The band assignment (wavenumbers and intensities) is made based on (B3LYP/6‐311 + + G**) calculations. Comparison of theoretical FT‐IR and FT‐RS spectra with those of SERS allows to obtain information on the orientation of these dipeptides as well as specific‐competitive interactions of their functionalities with the silver substrate. More specifically, V1 and V4 appear to interact with the silver substrate mainly via a  C_sgCH₃ moiety localized at the  N_amideC_sg(CH₃)P molecular fragment. In addition, the  POH and isopropyl units of V4 assist in the adsorption process of this molecule. In contrast, the  C_αNH₂ and  PO₃H⁻ groups of V2 and V3 interact with the silver nanoparticles, whereas their isopropyl and isobutyl fragments seem to be repelled by the silver substrate (except for the  CH₂  of V3), similar to the  C_β(CH₃)₂ fragment of L ‐Val for all L ‐Val phosphonate dipeptides investigated in this work. The adsorption mechanism of these molecules onto the colloidal silver surface is also affected by amide bond behavior. Copyright © 2010 John Wiley & Sons, Ltd.     

Spectroscopic and thermal studies on the inclusion of trans‐cinnamic acid and a number of its hydroxyl‐derivatives with α, β and γ‐cyclodextrins molecules

The inclusion compounds of α‐, β‐ and γ‐cyclodextrins (α‐CD, β‐CD and γ‐CD) with trans‐cinnamic acid (t‐CIA), 3‐hydroxy‐trans‐cinnamic acid (t‐3OHCIA), 4‐hydroxy‐trans‐cinnamic acid (t‐4OHCIA) and 3,4‐dihydroxy‐trans‐cinnamic acid (t‐3,4OHCIA) were prepared and characterized, in the solid state, by means of thermogravimetry and Raman spectroscopy. The effects of the inclusion process on the guest molecules and on the hydrogen bond interactions of the guest were studied by monitoring sensitive vibrational modes, such as CO, CC and ring C H stretching modes. By combining Raman and TG data with ab initio calculations and information from CSD database on similar compounds, inclusion geometries for the different compounds are proposed. The size of the host cavity and the maximization of host/guest hydrogen‐bonding contacts appear to be the main factors determining the inclusion geometries. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Raman spectroscopic investigation of a new self‐assembly monolayer material 4‐[N‐phenyl‐N‐(3‐methylphenyl)‐amino]‐benzoic acid for organic light‐emitting devices

We have synthesized 4‐[N‐phenyl‐N‐(3‐methylphenyl)‐amino]‐benzoic acid (4‐[PBA]) and investigated its molecular vibrations by infrared and Raman spectroscopies as well as by calculations based on the density functional theory (DFT) approach. The Fourier transform (FT) Raman, dispersive Raman and FT‐IR spectra of 4‐[PBA] were recorded in the solid phase. We analyzed the optimized geometric structure and energies of 4‐[PBA] in the ground state. Stability of the molecule arising from hyperconjugative interactions and charge delocalization was studied using natural bond orbital analysis. The results show that change in electron density in the σ* and π* antibonding orbitals and E₂ energies confirm the occurrence of intramolecular charge transfer within the molecule. Theoretical calculations were performed at the DFT level using the Gaussian 09 program. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution. The good agreement between the experimental and theoretical spectra allowed positive assignment of the observed vibrational absorption bands. Finally, the calculation results were applied to simulate the Raman and IR spectra of the title compound, which show agreement with the observed spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

A single‐crystal Raman and infrared study of the nonlinear optical crystal MBANP

Single‐crystal Raman and polycrystalline thin‐film infrared measurements have been obtained for the polar organic nonlinear optical material 2‐(α‐methylbenzylamino)‐5‐nitropyridine (MBANP). For comparison, thin‐film polycrystalline infrared measurements were also made on 2‐(α‐methylbenzylamino)‐3,5‐dinitropyridine (MBADNP). The long wavelength electronic absorption was measured in several solvents and as a thin solid film. The Raman spectra are dominated by three intense bands attributed to vibrations of the ring, the NO₂ substituent, and the N H bond. The most intense scattering and absorption arose from the α_bb component of the polarisability tensor. This implies that the most significant contribution to the transition polarisability arises from the electronic transition near 383 nm, polarised along the b‐axis of the crystal. The strongest bands in the infrared spectra are also associated with the same three bands, consistent with the predictions of the effective conjugation coordinate (ECC) theory, implying efficient electron–phonon coupling (or electronic delocalisation) in the conjugated system. DFT calculations of vibrational wavenumbers and eigenvectors were used to assign relevant vibrational features and to derive useful information about the molecular structure. This single‐crystal material is also a strong candidate for an efficient laser Raman converter with a large wavenumber shift of 3404 cm⁻¹ and a high damage threshold. Copyright © 2010 John Wiley & Sons, Ltd.     

FT‐IR and FT‐Raman investigations of the chemosensing material para‐hexafluoroisopropanol aniline

As an important chemosensing material involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para‐HFIP aniline (p‐HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance and mass spectrometry experiments. Fourier transform infrared absorption spectroscopy (FT‐IR) and FT‐Raman spectra of p‐HFIPA have been obtained in the regions of 4000–500 and 4000–200 cm⁻¹, respectively. Detailed identifications of its fundamental vibrational bands have been given for the first time. Moreover, p‐HFIPA has been optimized and vibrational wavenumber analysis can be subsequently performed via density functional theory (DFT) approach in order to assist these identifications in the experimental FT‐IR and FT‐Raman spectra. The present experimental FT‐IR and FT‐Raman spectra of p‐HFIPA are in good agreement with theoretical FT‐IR and FT‐Raman spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

A vibrational spectroscopic investigation of rhodanine and its derivatives in the solid state

Raman and infrared spectra are reported for rhodanine, 3‐aminorhodanine and 3‐methylrhodanine in the solid state. Comparisons of the spectra of non‐deuterated/deuterated species facilitate discrimination of the bands associated with N H, NH₂, CH₂ and CH₃ vibrations. DFT calculations of structures and vibrational spectra of isolated gas‐phase molecules, at the B3‐LYP/cc‐pVTZ and B3‐PW91/cc‐pVTZ level, enable normal coordinate analyses in terms of potential energy distributions for each vibrational normal mode. The cis amide I mode of rhodanine is associated with bands at ∼1713 and 1779 cm⁻¹, whereas a Raman and IR band at ∼1457 cm⁻¹ is assigned to the amide II mode. The thioamide II and III modes of rhodanine, 3‐aminorhodanine and 3‐methylrhodanine are observed at 1176 and 1066/1078; 1158 and 1044; 1107 and 984 cm⁻¹ in the Raman and at 1187 and 1083; 1179 and 1074; 1116 and 983 cm⁻¹ in the IR spectra, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

A DFT study on Diels–Alder cycloadditions of trans‐1,3‐butadiene to C60 and C70

Investigation of the relative reactivity of bonds in fullerenes will provide fundamental theory for the design of fullerene‐based materials. We have theoretically investigated the reactivity of the Diels–Alder (DA) cycloaddition of cis‐1,3‐butadiene to all types of bonds in C₆₀ and C₇₀ using the M06‐2X hybrid density functional theory (DFT) calculations (J. Phys. Org. Chem. 2012, 25 850–855) and have pointed out that the DA cycloadditions of cis and trans forms of 1,3‐butadiene to ethylene have a specially intimate relationship (J. Phys. Org. Chem. 2014, 27 652–660). For the aim of telling a whole story of the DA cycloaddition concerning C₆₀ and C₇₀, the DA cycloadditions of trans‐1,3‐butadiene to all types of bonds in C₆₀ and C₇₀ were explored at the same theoretical level as those of the cis‐1,3‐butadiene. The calculated results related with the trans‐ and cis‐1,3‐butadienes were compared. The potential energy curves of DA cycloadditions of trans‐ and cis‐1,3‐butadiene to C₆₀ and C₇₀ were discussed. The distortion–interaction energy model was employed to elucidate the origin of different reactivity of all kinds of C?C bonds. The solvent effects were examined using the continuum solvent model. These current results, along with our previous research, will help to obtain an overall view of the DA cycloadditions of 1,3‐butadiene to C₆₀ and C₇₀. Copyright © 2014 John Wiley & Sons, Ltd.