Effects of dipole interaction and solvation on the CO stretching band of N,N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the CO stretching (ν_CO) band of N,N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl₄ has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν_CO envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν_CO envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν_CO band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl₄ solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν_CO band observed in a highly diluted CCl₄ solution (≤0.023 M) indicate that the solvation effect of CCl₄ is more complicated than those of cyclohexane and n-hexane. The analyses of the ν_CO band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.     

Atmospheric chemistry of CF3CFCH2: Products and mechanisms of Cl atom and OH radical initiated oxidation

The products of Cl atom and OH radical initiated oxidation of CF₃CFCH₂ were studied in 700 Torr of N₂/O₂ diluent at 296 ± 1 K. The reactions of Cl atoms and OH radicals with CF₃CFCH₂ proceed via electrophilic addition to the double bond. The reaction with chlorine atoms proceeds 56 ± 5% via addition to the central carbon. The chlorine atom initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F in a molar yield which is indistinguishable from 100% and independent of [O₂], and HC(O)Cl in a molar yield which increased from 30% to 59% as [O₂] was increased from 3 to 700 Torr. The OH radical initiated oxidation of CF₃CFCH₂ gives CF₃C(O)F as major product in a yield of 91 ± 6%. The results are discussed with respect to the atmospheric chemistry and environmental impact of CF₃CFCH₂.     

Bonding trends in MCH2 systems: Simple orbital interpretation and evidence for double bonds

MCH₂ systems, where M is a metal from 4th up to 7th period, are studied at DFT level using B3LYP functional and small-core quasirelativistic pseudopotential or fully relativistic four-component methodology. We obtained structural data for 44 elements, M, and our results can be used to infer double-bond lengths for these elements. Our results also suggest that the bonding of these MCH₂ systems can be understood by a simple pictorial approach, even when spin–orbit effects are present.     

(E)-1,2-Difluoro-1-iodo-2-trialkylsilanes—A useful synthon for the addition of the [IFCCF] unit to activated electrophiles

Fluoride ion catalyzed reaction of (E)-IFCCFSiR₃ with activated aromatic aldehydes and ketones and activated perfluoroaromatics, such as pentafluoropyridine and perfluorotoluenes, transfers the [IFCCF] unit to the activated electrophiles to stereospecifically provide (E)-1,2-difluoro-1-iodosubstituted derivatives. Aluminum chloride catalyzed reaction of (E)-1,2-difluoro-1-iodo-2-trialkylsilanes with alkyl or aryl acyl halides gives the corresponding (E)-1,2-difluoro-1-iodoketones stereospecifically in excellent yield. The vinyl iodide product formed via this methodology could be coupled (with Pd(0)) catalysis to provide an entry to a polyfunctionalized derivative.     

Conformational influences of the polymorphic forms on the CO and C–H stretching modes of five saturated monoacid triglycerides studied by Raman spectroscopy at various temperatures

A study of the vibrational behavior of five saturated monoacid triacylglycerides is performed by Raman spectroscopy at various temperatures in two separate spectral ranges: 1780–1700 and 3100–2650 cm⁻¹. The samples are studied in polycrystalline phase at room temperature, in isotropic liquid phase, and in polycrystalline phase after cooling from the isotropic liquid phase. The CO stretching mode of these triglycerides changes significantly according to the temperature: we observe three components, or an unresolved doublet, or a resolved doublet. The I(2845)/I(2880) ratios (in the C–H stretching spectral region) of the different saturated monoacid triglycerides vary also according to the temperature. The study of these two indicators (the CO stretching mode and the I(2845)/I(2880) ratio) has permitted us to determine the polymorphic forms of the studied triglycerides.     

DFT study on second-order nonlinear optical properties of the derivatives of 7-vertex cobalt–carborane metallocenyl

Density functional theory (DFT) B3LYP method was employed to calculate electron properties and the second-order nonlinear optical (NLO) responses of the derivatives which were formed by (C₅H₅)Co(C₂B₄H₆) and CHCHC₆H₄NO₂, CHCHC₆H₄NH₂. The results show: when H atom of (C₅H₅)Co(C₂B₄H₆) is substituted by CHCHC₆H₄NO₂, the β_tot values of isomers are all slightly smaller than that of ferrocene (Fc) derivative (FcCHCHC₆H₄NO₂). However, when H atom of (C₅H₅)Co(C₂B₄H₆) is substituted by CHCHC₆H₄NH₂, the β_tot values of isomers are close to that of ferrocene (Fc) derivative (FcCHCHC₆H₄NH₂). It indicates that (C₅H₅)Co(C₂B₄H₆) can be either a donator or an acceptor.     

Nucleophilic destruction of organophosphate toxins: A computational investigation

Computed reaction enthalpies, free energies, and activation barriers in vacuo are presented for the nucleophilic detoxification of the organophosphorus compounds (H)(HO)P(O)F, (H)(H₃CO)P(O)F and (H₃C)(CH(CH₃)₂O)P(O)F via the reaction R₁OH + (R₂)(R₃O)P(O)F → (R₂)(R₃O)P(O)(OR₁) + HF for a wide variety of R₁OH nucleophiles. Density functional theory at the B3LYP/6-311++G(d,p) computational level was employed for all the calculations. A multi-step Wright-type reaction mechanism [J. B. Wright, W.E. White, J. Mol. Struct. (THEOCHEM) 454 (1998) 259], which proceeds via a proton transfer from the nucleophile to the fluorine atom through the phosphinyl oxygen atom, was consistently found to have a lower activation barrier in the gas-phase than for the corresponding mechanism that operates via a proton transfer from the nucleophile directly to the fluorine atom. Of the nucleophilic agents investigated, peroxybenzoic acid and o-iodosobenzoic acid had the lowest classical activation barrier for the Wright-type mechanism.     

Specific crystal structure of poly(3-hydroxybutyrate) thin films studied by infrared reflection–absorption spectroscopy

Infrared reflection–absorption (IR-RAS) and transmission spectra were measured for poly(3-hydroxybutyrate) (PHB) thin films to explore its specific crystal structure in the surface region. As IR-RAS is sensitive to the vibration mode of perpendicular orientation of the surface, differences between IR-RAS and transmission spectra indicate an orientation of the lamella structure in the surface of PHB thin films. The relative intensity of the crystalline CO stretching band in the IR-RAS spectrum is significantly weaker than that in the transmission spectrum. It may be concluded that the transient dipole moment of the CO stretching mode of the crystalline state is not oriented perpendicular but nearly parallel to the substrate surface. On the other hand, the relative intensity of the band at 3009 cm⁻¹ due to the C–H stretching mode of the C–HOC hydrogen bonding is similar between the IR-RAS and transmission spectra, suggesting that the C–H bond is oriented neither perpendicular nor parallel to the substrate surface but in an intermediate direction. Since the CO group of the C–HOC hydrogen bonding is oriented nearly parallel to the surface and its C–H group is in the intermediate direction, it is very likely that the C–HOC hydrogen bonding has a somewhat bent structure. These results are in good agreement with our previous conclusion that the C–HOC hydrogen bonding of PHB exists along the a-axis (not the b-axis) between the CH₃ group of one helix and the CO group of another helix.     

Magnetic field effect on chemical compositions of spherical Fe/Co fine particles synthesized from a gaseous mixture of iron pentacarbonyl and cobalt tricarbonyl nitrosyl

Under UV light irradiation on a gaseous mixture of Fe(CO)₅ and Co(CO)₃NO, both the crystalline deposits with sizes of 5 and 18 μm and the spherical particles with a mean diameter of 0.3 μm were produced. From FT-IR spectra and SEM–EDS analysis, it was suggested that the chemical structure of the crystalline deposits was the one of Fe₂(CO)₉ being modified by involving Fe(CO)Co bond. By decreasing a partial pressure of Fe(CO)₅ to 0.5 Torr in the gaseous mixture, only the spherical aerosol particles could be produced. Chemical composition of the particles was rich in Co species. From the disappearance of bridging CO band in the FT-IR spectra of the particles and the appearance of CO bands coordinated to a metal atom, Fe atom in Fe(CO)₄ was suggested to be coordinated by the O atom in bridging CO bond in Co(CO)Co structure and/or in α-diketone structure which was formed from two CO groups in dicobalt species. Chemical compositions of the crystalline deposits and the spherical particles were influenced differently by the application of a magnetic field. Atomic ratio of Fe to Co atom decreased in the crystalline deposits whereas it increased in the spherical particles with increasing magnetic field up to 5 T. Linearly aggregated particles (i.e., particle wires) as long as 30 μm were produced on the front side of a glass plate placed at the bottom of the irradiation cell.     

Heterobimetallic aluminium and zinc complex with N-arylanilido-imine ligand: Synthesis, structure and catalytic property for ring-opening polymerization of ε-caprolactone

Treatment of a N-arylanilido-imine ligand [ortho-C₆H₄(NHAr)CHN]₂CH₂CH₂ (Ar = 2,6-Me₂C₆H₃) (LH₂) with one equiv. of AlMe₃ affords a monometallic complex [C₆H₄(NHAr)–CHN)]CH₂CH₂(C₆H₄(NAr)CHNAlMe₂) (1). The monometallic complex 1 reacts with one equiv. of ZnEt₂ to give a heterobimetallic complex [C₆H₄(NAr)–CHNZnEt]CH₂CH₂[C₆H₄(NAr)–CHNAlMe₂] (2). Both complexes were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses, and the molecular structures of 1 and 2 were determined by X-ray diffraction analysis. The complexes 1 and 2 both are efficient catalysts for ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol yielding polymers with narrow polydispersity values and complex 2 initiates the polymerization in a controllable manner.     

Unimolecular chemistry of metastable dimethyl isophthalate radical cations

The MS/MS spectrum of the metastable molecular ions of dimethyl isophthalate 1 differs from that of the isomeric dimethyl terephthalate 2 by the observation of, inter alia, a quite intense loss of C,H₂,O ascribed to formaldehyde. Results obtained using a combination of mass spectrometry techniques suggest that this process could consist of an isomerization reaction of the molecular ion into an ion–neutral complex (INC) linking a benzoyl radical and neutral formaldehyde to a proton [ArCOHOCH₂]⁺. Within the complex, a proton transfer catalyzed by formaldehyde occurs resulting in the production of an ionized cyclohexadienylidene methanone (ketene) structure.     

Investigations of molecular interactions in propionic acid–N,N-dimethyl formamide binary system—FTIR study

FTIR spectra of propionic acid (PA), N,N-dimethyl formamide (DMF) and its binary mixtures with varying molefractions of the PA were recorded in the region 500–3500 cm⁻¹, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), δ(OC–N) and ν_as(CN) of DMF, ν(CO) and ν(CO) of PA have been explained in terms of the hydrogen bonding interactions between DMF and PA and dipole–dipole interaction. The intrinsic bandwidth for the vibrational modes ν_as(CN) and ν(CO) has been elucidated using Bondarev and Mardaeva model.     

A bonding study of cyclopentene (c-C5H8) adsorption on Ni(1 1 1) surface

The adsorption of cyclopentene (c-C₅H₈) on Ni(1 1 1) was studied using DFT and semiempirical calculations. Preferred site and geometry calculations were carried out considering a Ni(1 1 1) surface and a unit cell of 64-atoms. The tetrahedral threefold hollow position was identified as the most favorable site, with a surface-molecule minimum distance of 1.83 Å. A bending structure is adopted when the molecule is adsorbed where the carbon atoms of the double bond are closer to the surface forming an angle of 160° among non-equivalents carbon atoms. The metal surface was represented by a two-dimensional slab with an overlayer of c-C₅H₈/Ni of 1/9 ratio. We also computed the density of states (DOS) and the crystal orbital overlap populations (COOP) corresponding to CC, CNi, CH, and NiNi bonds. We found that both NiNi bonds interacting with the ring, and the CC bond are weakened after adsorption, this last bond is linked significantly to the surface. The hydrogen atoms belonging to the saturated carbon atoms also participate in the adsorbate–surface bonding. The main interactions include the 4s, 3p_z and 5d_z² bands of nickel and 2p_z bands of the carbon atoms of the double bond.     

Synthesis and characterization of new heterocyclic Schiff base palladacycles: Ring activation through N-oxide formation

Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂], (1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂]}₂(OCOCH₃)₂], (2), with two ligands coordinated through the pyridine nitrogen. Treatment of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂], (4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(OCOCH₃)]₂, (5) with metallation of an aromatic phenyl carbon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged complexes [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)]₂, (6) and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Br)]₂, (7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave the mononuclear species [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)(PPh₃)], (8) and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}-(Br)(PPh₃)], (9), as air stable solids. Treatment of 6 and 7 with Ph₂P(CH₂)₂PPh₂ (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][Cl], (10), and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][PF₆], (11), with a chelating diphosphine. The molecular structure of complex 9 was determined by X-ray single crystal diffraction analysis.     

Weak hydrogen-, halogen- and stacking ππ bonding in crystalline 5-chloro-1-indanone. An analysis by using X-ray diffraction, vibrational spectroscopy and theoretical methods

Intermolecular forces of C–HO, C–Hπ, COCl and ππ types are present in the stable triclinic crystal structure of 5-chloro-1-indanone. They are analysed from a geometrical point of view supported in some extent by the analysis of the vibrational spectrum of the titled compound. Moreover, the molecular structure of the isolated species is calculated by using ab initio as well as density functional theory (DFT) methods together an assortment of basis sets. In order to obtain some information about the influence of intermolecular forces on the molecular structure, the calculated geometries of a free molecule were compared with the experimental solid phase geometry determined by X-ray crystallography.An analysis and assignment of the vibrational spectrum of the 5-chloro-1-indanone is accomplished by using IR and Raman experimental data along with Pulay et al.’s scaled quantum mechanical force field (SQM) methodology starting from the theoretical B3LYP/6-31G(d) and BLYP/6-31G(d) force fields under C_s symmetry.     

Fourier transform infrared study of mercury interaction with carboxyl groups in humic acids

An interaction between humic acid, an organic part of soil and mercury was studied by Fourier transform infrared spectroscopy (FTIR) and by ICP-AES analysis under given pH and concentration conditions. First the spectroscopic model was validated on the interaction of simple molecules representing the structural components of humic acid such as benzoic acid, catechol and salicylic acid with mercury. The interaction of carboxylic parts of humic acid with mercury is very interesting and easily characterised by infrared spectroscopy, an ideal mean for molecular study. Under the salt form (commercial humic acid Fluka TM: FHA), humic acid reacts with mercury in a different way from its acid form (FHA purified noted PFHA) and the Leonardite (LHA). Because of the straightforward exchange between Na⁺, Ca²⁺ and Hg²⁺, fixation of the latter is much more important with the salt form (FHA). However, this reaction is reduced under the acid form (PFHA, LHA) because the exchange with protons is difficult. The effect of this exchange was studied by FTIR showing the intensity decrease of ν_CO (COOH), the carboxylic functional group band of the acid, and the shifting of ν_as (COO⁻), the carboxylate functional group band under given pH and mercury conditions. For the FHA salt form, the characteristic band ν_CO (COOH) represented by a shoulder did not evolute, whereas the corresponding band to ν_as (COO⁻) strongly shifted (40 cm⁻¹) for a maximum Hg²⁺ concentration (1 g l⁻¹). On the other hand, for the acid form (PFHA, LHA), the intense band of ν_CO (COOH) disappeared proportionally to the increase of Hg²⁺concentration and the ν_as (COO⁻) band moved for about 20 cm⁻¹. The same results were reached with pH variations. Our results were confirmed by ICP-AES mercury analysis. This study shows that humic acids react differently according to their chemical and structural state.     

Seeking new metalloligands: Synthesis and reactivity of palladacycles with pyridine and pyrimidine rings

Treatment of the Schiff base ligands 4-(NC₅H₄)C₆H₄C(H)N[2′-(OH)C₆H₄] (a), 3,5-(N₂C₄H₃)C₆H₄C(H)N[2′-(OH)-C₆H₄] (b) and 3,5-(N₂C₄H₃)C₆H₄C(H) N[2′-(OH)-5′-^tBuC₆H₃] (c) with palladium (II) acetate in toluene gave the poly-nuclear cyclometallated complexes [Pd{4-(NC₅H₄)C₆H₃C(H)N[2′-(O)C₆H₄]}]₄ (1a), [Pd{3,5-(N₂C₄H₃)C₆H₃C(H)N[2′-(O)-C₆H₄]}]₄ (1b) and [Pd{3,5-(N₂C₄H₃)C₆H₃C(H)N[2′-(O)-5′-^tBuC₆H₃]}]₄ (1c) respectively, as air stable solids, with the ligand acting as a terdentate [C,N,O] moiety after deprotonation of the –OH group. Reaction of the cyclometallated complexes with triphenylphosphine gave the mononuclear species [Pd{4-(NC₅H₄)C₆H₃C(H) N[2′-(O)C₆H₄]}(PPh₃)], (2a), [Pd{3,5-(N₂C₄H₃)C₆H₃C(H) N[2′-(O)C₆H₄]}(PPh₃)], (2b) and [Pd{3,5-(N₂C₄H₃)C₆H₃C(H)N[2′-(O)-5′-^tBuC₆H₃)}(PPh₃)], (2c) in which the polynuclear structure has been cleaved and the coordination of the ligand has not changed [C,N,O]. When the cyclometallated complexes 1b and 1c were treated with the diphosphines Ph₂P(CH₂)₄PPh₂ (dppb), Ph₂PC₅H₄FeC₅H₄PPh₂ (dppf) and Ph₂P(CH₂)₂PPh₂ (t-dppe) in a 1:2 molar ratio the dinuclear cyclometallated complexes [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H)N{2′-(O)C₆H₄}]}₂(μ-Ph₂P(CH₂)₄PPh₂)], (3b), [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H) N{2′-(O)-5′-^tBuC₆H₃}]}₂(μ-Ph₂P(CH₂)₄PPh₂)], (3c), [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H)N{2′-(O)C₆H₄}]}₂(μ-Ph₂P(η⁵-C₅H₄)Fe(η⁵-C₅H₄)PPh₂)], (4b), [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H) N{2′-(O)-5′-^tBuC₆H₃}]}₂(μ-Ph₂P(η⁵C₅H₄)Fe(η⁵C₅H₄)P-Ph₂)], (4c) and [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H)N{2′-(O)-5′-^tBuC₆H₃}]}₂(μ-Ph₂P(CHCH)PPh₂)], (5c) were obtained as air stable solids.     

Structural and vibrational studies of molecular conductors using quantum mechanical methods: 1,3-Dithiole-2-thione, 1,3-dithiole-2-one, 1,3-dioxole-2-one and 1,3-dioxole-2-thione

Computations were carried out by employing the RHF and density functional theory (DFT) methods to investigate the geometries, atomic charges, harmonic vibrational frequencies for the 1,3-dithiole-2-thione (DTT), 1,3-dithiole-2-one (DTO), 1,3-dioxole-2-thione (DOT) and 1,3-dioxole-2-one (DOO) molecules and their radical cations. The geometrical parameters and atomic charges on various atomic sites of the DTT and DOT molecules and their radical cations suggest extended conjugation in these systems. Contrary to this, for the DOO⁺ and DTO⁺ ions there is no evidence in favour of such conjugation, however, the neutral molecules exhibit some conjugation. Harmonic forced field and vibrational mode calculations provided convincing theoretical evidence for the reassignment of some fundamental vibrational modes for all the four molecules. In going from the neutral species to the charged ions for all the four cases the CC stretching frequency is found to decrease drastically. The CS stretching frequency reduces drastically for the DTT and DOT molecules as compared to their radical cations whereas the CO stretching frequency is found to increase in going from the neutral molecule to its radical cation for the DOO and DTO molecules. The ring stretching mode with a₁ symmetry and CC and CO/S stretching modes in these molecules appear to help in conversion of neutral molecule into respective radical cation and neighbouring radical cation into respective neutral molecule. Thus, there appears the feasibility of stretching vibrational mode coupling with electron transfer.     

Vibrational spectroscopy of 4-hydroxybenzhydrazide and its O,N-deuterated isotopologue accompanied by X-ray structure refinement

The vibrations of crystalline 4-hydroxybenzhydrazide were investigated by IR and Raman spectroscopy. Spectral changes resulting from O,N-deuteration together with DFT calculations were employed for band assignment presented in terms of potential energy distribution. The characteristic absorptions of the hydrazide group were located at 1623 (CO stretching), 1588 (NH₂ bending) and 1532 cm⁻¹ (NH bending). The greatest contributions of the NN and CN stretching vibrations were found in the 1208 and 1109 cm⁻¹ modes, respectively. The predominant contribution of the CO stretching vibration was observed for the 1282 cm⁻¹ absorption. The computations at the B3LYP level with 6-311++G(d,p) basis set were based on structural parameters taken from refined single crystal X-ray investigations. The details of hydrogen bonding and crystal packing are also presented.     

Blue-shifting intramolecular CH O(S) contacts in sterically strained systems

A group of model systems which may form chelate-type structures with intramolecular CH  Y (Y = O, S) contact is investigated computationally. The existence of several conformers permits to identify a reference molecule without the CH  Y intramolecular contact and to establish the blue-shifting character of this interaction. The CH stretching frequency in chelate forms is found to increase with respect to its value in the reference system. A parallel decrease of the CH bond distance is also established. The blue-shifting character of the intramolecular CH  Y contact is interpreted in terms of the sterically enforced repulsion between the hydrogen atom in CH and the electron donor Y. This interpretation is supported by the negative (repulsive) estimates of the energy contribution due to CH  Y contacts.