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n-Pentanol has been considered as a promising alternative fuel for compression-ignition engines due to its potential to reduce greenhouse gases and pollutant emissions. Engine performance is strongly dominated by fuel oxidation chemistry, and thus a more accurate determination of the coefficients of the reactions ruling its oxidation is essential for the utilization of n-pentanol in combustion engines. The reactions involving 1‑hydroxy‑1-pentyl and molecular oxygen were found to play an important role in controlling the low temperature oxidation chemistry, but have not been investigated experimentally or theoretically; this is also the case for the reactions of the 1‑hydroxy‑1-peroxypentyl radical, which is formed by the addition of oxygen to the radical center of 1‑hydroxy‑1-pentyl. This work presents a theoretical study with high level ab initio calculations at the CCSD(T)/aug-cc-pVTZ//M06-2X/cc-pVTZ level of theory to shed light on the fate of the 1‑hydroxy‑1-peroxypentyl radical. The rate coefficients of all the possible intra-molecular hydrogen shift reactions of that radical were computed using variational transition state theory with small curvature tunneling corrections. For certain reactions, tunneling and variational effects are very pronounced, proving the need for robust methodologies to account for these effects. The hydrogen shift reaction leading to a concerted HO2 elimination and formation of n-pentanal is the dominant pathway and governs the reactivity of 1‑hydroxy‑1-peroxypentyl radical at any temperature. The reverse of this reaction was thereby investigated as well. For this prominent pathway, the effects of multistructural (multiple conformers) torsional anharmonicity of the stationary points were taken into account in order to refine the forward and reverse rate coefficients. The rate coefficients calculated at room temperature are compared to those calculated using a previously developed cost-effective multi-conformer transition state theory approach. The system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) theory was used to compute the pressure-dependent rate coefficients, which indicate significant pressure dependence at intermediate and high temperatures. Implementation of the calculated reaction rate coefficients in chemical kinetics models of n-pentanol revealed that our computed rate coefficients enable better insights into the chemistry of n-pentanol, and help to understand how n-pentanal is formed.

Absolute intensities of the ΔvOH = 1 − 2 and ΔvOD = 1 − 3 transitions were determined for a range of alcohols (methanol, ethanol, 2-propanol, 1-propanol and tert-butanol) using conventional Fourier transform infrared (FTIR) spectroscopy. The intensities of the OH stretching transitions are stronger than the corresponding OD stretching transitions and become increasingly stronger with higher overtone transitions as expected from the reduced masses of the oscillators. Furthermore, accurate absolute intensities of the third and fourth OH stretching overtone transitions were determined using our newly constructed integrated cavity ring down (CRD) and FTIR spectrometer with experimental uncertainties generally less than 10%. The experiments were complemented by local mode calculations, with the potential energy surfaces and the dipole moment functions determined at the CCSD(T)/aug-cc-pVTZ level of theory. The calculated oscillator strengths of the ΔvOH = 4 − 5 transitions are within 25% of the experimental results.

Vibrational transition frequencies and oscillator strengths of the FH-stretching transitions in the FH⋯CO, FH⋯FH, FH⋯CO 2 and FH⋯N 2 complexes were calculated with different vibrational models. The calculated vibrational frequencies were found to agree well with experimental values. The experimental oscillator strengths of the FH-stretches in the FH monomer and FH dimer were also predicted well by the different vibrational models. However, with our best theoretical methods there is still a factor of 2–4 between the experimental and calculated oscillator strengths for the FH-stretches in the FH⋯CO, FH⋯CO 2 and FH⋯N 2 complexes.

The local mode perturbation theory (LMPT) model was developed to improve the description of hydrogen bonded XH-stretching transitions, where X is typically O or N. We present a modified version of the LMPT model to extend its application from hydrated bimolecular complexes to hydrogen bonded bimolecular complexes with donors such as alcohols, amines and acids. We have applied the modified model to a series of complexes of different hydrogen bond type and complex energy. We found that the differences between local mode (LM) and LMPT calculated fundamental XH-stretching transition wavenumbers and oscillator strengths were correlated with the strength of the hydrogen bond. Overall, we have found that the LMPT model in most cases predicts transition wavenumbers within 20 cm−1 of the experimental values.

The layered double hydroxides (LDH) have been widely investigated for their use as sorbents, exchangers and delivery shuttles for anionic compounds in aqueous environments. We synthesized hydrotalcite (HT), calcined it to increase its sorption capacity and quantified the affinities of chloride and sulphate for intercalation, in mixed anion solutions. To better simulate natural systems, no particular measures were taken to exclude air, with its inherent CO 2 . Thus, a small amount of dissolved carbonate ( 2 , always contains some interlayer carbonate; ii) chloride competes with carbonate for intercalation sites, whereas sulphate does not; iii) when chloride and sulphate are present in equal concentrations, the affinity of sulphate is higher than chloride for intercalation, regardless of the total anion concentration; iv) at anion concentrations 2 + , Al 3 + LDH that forms in multi ion solutions. This can be used to predict geochemical behavior in natural systems such as determining saturation states of minerals and to optimize wastewater treatment and remediation of contaminated soil and groundwater.

The effect of adding electron donating and withdrawing groups on the dihydroazulene (DHA)/vinylheptafulvene (VHF) photochromic system has been investigated using Raman spectroscopy in CS2 solutions. The photoswitching between DHA and VHF is often characterised with UV-Vis spectroscopy. However, Raman spectroscopy can also be used for this purpose and give structural insight, as the light induced ring-opening from DHA to VHF causes changes in the CN-stretching frequencies. The CN-stretching frequencies in DHA and VHF are isolated and optimal for the identification of DHA and VHF. The DHA system is also investigated in the solid state.

Amines have many atmospheric sources and their clusters play an important role in aerosol nucleation processes. Clusters of a typical amine, dimethylamine (DMA), of different sizes were measured with matrix isolation IR (infrared) and NIR (near infrared) spectroscopy. The NIR vibrations are more separated and therefore it is easier to distinguish different sizes of clusters in this region. The DMA clusters, up to DMA tetramer, have been optimized using density functional methods, and the geometries, binding energies and thermodynamic properties of DMA clusters were obtained. The computed frequencies and intensities of NH-stretching vibrations in the DMA clusters were used to interpret the experimental spectra. We have identified the fundamental transitions of the bonded NH-stretching vibration and the first overtone transitions of the bonded and free NH-stretching vibration in the DMA clusters. Based on the changes in vibrational intensities during the annealing processes, the growth of clusters was clearly observed. The results of annealing processes indicate that DMA molecules tend to form larger clusters with lower energies under matrix temperatures, which is also supported by the calculated reaction energies of cluster formation.

The hydroxy peroxy radical derived from the oxidation of 3-methyl-3-buten-1-ol (MBO331), can undergo four different hydrogen shift (H-shift) reactions. We have compared optimized geometries, barrier heights and reaction rate constants obtained with five different DFT functionals (BLYP, B3LYP, BHandHLYP, wB97X-D and M06-2X) with the aug-cc-pVTZ basis set. We found that the single-point CCSD(T)-F12A/VDZ-F12 energies calculated at the different DFT geometries had very similar barrier heights. The wB97X-D, M06-2X and CCSD(T)-F12A/VDZ-F12 barrier heights are comparable. The atmospheric decomposition of the MBO331 peroxy radical was found to undergo a 1,5-CH H-shift reaction with a reaction rate constant of about 1 s−1.

There are some discrepancies in both the vibrational assignments and in the metal-ligand (M-L) bond strengths predicted in the previous studies on the copper (II) chelated complex of dibenzoylmethane, Cu(dbm)2. Also, there is a lack of theoretical structure, Raman spectrum and full vibrational assignment for Cu(dbm)2 in the literatures. Density functional theory (DFT) at the B3LYP level and also MP2 calculations using different basis sets, besides Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses, have been employed to investigate the effect of methyl substitution with the phenyl group on the stabilities of bis(acetylacetonate) copper (II), Cu(acac)2, and Cu(dbm)2 complexes and the electron delocalization in their chelated rings. Measured solid phase infrared and Raman bands for Cu(dbm)2 complex have been interpreted in terms of the calculated vibrational modes and detailed assignment has been presented. We concluded that, theoretically, the results of charge transfer studies, and experimentally, in-phase symmetric O-Cu-O stretching mode of these complexes are very useful measures for M-L bond strength. The electron delocalization in the chelated rings and the M-L bond strength in Cu(dbm)2 are concluded to be higher than those in Cu(acac)2. The calculated geometries and vibrational results are in good agreement with the experimental data.

We have recorded the third OH-stretching overtone region of vapor phase methallyl- and allyl-carbinol with intracavity laser photoacoustic spectroscopy to investigate the effect of the methyl group in methallyl carbinol on the weak intramolecular OH⋯π hydrogen bond. We have used atoms in molecules theory, non-covalent interactions calculations and natural bond orbital analysis to describe the intramolecular OH⋯π hydrogen bond. An increased intramolecular interaction was predicted and confirmed experimentally by an observed larger redshift of the OH-stretching overtone transition of the most abundant conformer of methallyl carbinol relative to that of the corresponding conformer of allyl carbinol.

We have calculated band profiles of the hydrogen bonded OH-stretching bands in H 2 O · H 2 O, using a local mode Hamiltonian which includes the low-energy acceptor wagging and the high energy OH-stretching motion. We use the method previously developed for coupling of OH- and OO-stretching modes. Our current results confirms that low frequency modes will lead to wider OH-stretching bands. The spread of intensity and shape of the profile from coupling to the acceptor wagging mode is different to that found from coupling to the OO-stretching mode. Combination of both results yields an OH-stretching band profile, which is around 250 cm −1 wide in the third OH-stretching overtone.

The syntheses and characterisation of the Co(III) complexes [(L)Co(O 2 CO)]ClO 4 (L = a tripodal tetraamine ligand = baep, abap, uns-penp, dppa, trpn) are reported. Geometric isomers are possible for all but the trpn complex, owing to the non-equivalence of the three arms on the tripodal ligand, and both NMR and X-ray crystallography are used to identify the single isomer formed. X-ray crystal structures of the complexes [(L)Co(O 2 CO)]ClO 4 · x H 2 O (L = baep, x = 0.5; L = abap, x = 0; L = uns-penp, x = 1; L = dppa, x = 0; L = trpn, x = 1) are reported; little variation is observed in the geometry of the carbonate chelate ring while significant lengthening of bonds and expansion of angles involving the cobalt ion occurs as the number of six-membered chelate rings in the complex cations increases. 59 Co NMR chemical shift data for the complexes show the expected linear relationship between λ max , the wavelength of the lowest energy d – d transition, and γ, the magnetogyric ratio of the 59 Co nucleus. An excellent correlation between Δ, the d orbital splitting parameter, and δ( 59 Co) also exists for these complexes. Rate data for the acid hydrolysis of [(L)Co(O 2 CO)] + (L = uns-penp, dppa) in 1.0 M HClO 4 differ by two orders of magnitude, and this is attributed to the differing steric accessibility of the endo O atoms in each complex. DFT calculations on the complexes reproduce the isomeric preferences, UV–Vis and 59 Co NMR spectroscopic data well, provided that solvent effects are included.

We have calculated relative energies and dipole moments of the stable conformers of nitrous acid, ethanol, ethylene glycol and propanone nitrate using a range of ab initio methods and basis sets. We have used these to calculate conformationally weighted dipole moments that are useful in estimates of collision rates between molecules and ions. We find that the average error in the conformationally weighted dipole moments is less than 5% for CCSD(T) with the aug-cc-pVTZ basis set, less than 10% for B3LYP/6-31G(d) and less than 20% for B3LYP/6-31+G(d) and B3LYP/aug-cc-pVTZ.

Dyad (η4-C4Ph4)Co(η5-C5H4CH CHFc) (2) containing isolobal iron and cobalt metallocene fragments has been prepared and its structure and spectroelectrochemical properties examined. Both the E and Z isomers have been characterised and their X-ray structures determined. B3LYP/6-31G∗ calculations for 2 show that the HOMO has more electron density on the Fc than on the CbCo(η5-C5H4) fragment whereas the reverse is the case for the LUMO. Both isomers undergo chemically reversible oxidations at the Fc (0.49 and 0.53 V) and CbCo redox centres (0.96 V) but the [2Z]2+ cation isomerises to [2E]2+ concomitant with the second oxidation process. A NIR band at 1290 nm for the [2E]+ cation is assigned to a CbCo(η5-C5H4) → Fc+ charge-transfer.

This paper describes the orbital configuration which provides a basis for the understanding of the electronic structure and spectroscopic properties of 17e and 18e FcC2R and FcC4R dyads, where R is H, 1-naphthyl, 9-anthryl, 3-pyrenyl, perylenyl. DFT calculations show that destabilisation of the ferrocenyl π orbitals upon binding a C CR group to a Cp ring leads to the metal-based a1 orbital dropping below the e1-a so that the frontier orbital configuration is ( e 2 ′ -a, π ) 2 ( e 2 ′ -b,metal ) 2 ( e 1 ′ -a, π ) 2 , (a1, metal)2. The contribution of the aryl group to the π e2-a and e1-a orbitals varies with the annelation of the ring. The LUMO is aryl based. The calculations are consistent with the spectroscopic data for the 18e species. Oxidation to the 17e cations does not change the orbital configuration but the orbital energies are lowered by the positive charge centred on the Fe. A strongly solvatochromic transition in the near-IR, a signature for the 17e cations, is best described as an LMCT transition but the contribution of C2R and C4R to the donor and acceptor levels depends on the ionization energy of the aryl π orbital. LMCT energies decrease from FcC2R to FcC4R dyads.

Trimethyl amine (TMA) exhibits the largest known difference in CH bond lengths within a methyl group, due to what is known as the lone pair trans effect. Dimethyl sulfide also exhibits this effect, but to a far lesser extent, making it ideal for comparison to TMA. In this paper, the first through fourth overtone spectra of N(CH 3 ) 3 , N(CD 3 ) 3 , N(CD 2 H)(CD 3 ) 2 , N(CH 3 )(CD 3 ) 2 , N(CD 3 )(CH 3 ) 2 and S(CH 3 ) 2 are reported and all major bands are assigned. The intensities of the observed bands are compared to intensities predicted by the harmonically coupled anharmonic oscillator local mode model. Good correlation is found between the experimental intensities and those predicted with the local mode model and HF/6-311++G(2d,2p) calculated dipole moment functions. An increase in the ability to resolve peaks as methyl groups are deuterated suggests that the lone pair mediates increased coupling between methyl groups.

Synthesis of 2′,4′,6′-trihydroxy-3′-methyldihydrochalcone, isolated as a natural product for the first time ( ex Leptospermum recurvum ), proceeds through 2′,4′,6′-trihydroxy-3′-formyldihydrochalcone. Two stable rotamers of this formyl derivative have been identified and the problems associated with NMR assignments of this type of compound have been attributed to conformational exchange. Rotamer ratios from molecular modelling and ab initio calculations agree well with those obtained from low temperature NMR studies. There is also excellent correlation between experimental NMR chemical shifts for the hydrogen-bonded hydroxyl protons with those derived from ab initio calculations. This formyl dihydrochalcone showed promising bioactivity in antiviral and antimicrobial assays.

The gas phase vibrational overtone spectra of trans-2-butene and cis-2-butene are recorded in the Δν CH =1−6 regions by Fourier transform infrared and conventional near infrared-visible spectroscopy. Overtone spectra in the Δν CH =5−9 regions are recorded by intracavity dye/titanium: sapphire laser photoacoustic spectroscopy. Absolute oscillator strengths are obtained from the conventional spectra. Oscillator strengths are calculated with a harmonically coupled anharmonic oscillator local mode model and ab initio dipole moment functions. The experimental and calculated oscillator strengths are compared. Spectral absorptions that are not due to transitions to pure local mode states or to local mode combination states, are observed in the spectra of both molecules, and are believed to be due to absorptions that involve methyl group torsion.

We have calculated two-photon electronic transitions for sulfuric acid ( H 2 SO 4 ) in the ultraviolet region using coupled cluster quadratic response theories combined with correlation consistent basis sets. We have investigated how the intensity of two-photon electronic transitions in H 2 SO 4 depends on the wavelength of the photons absorbed. We find that the intensity is more or less constant in the wavelength region in which the density of solar flux is of any importance. We have calculated the J-values for the photodissociation of H 2 SO 4 with absorption of two photons and compared these with previously calculated J-values for one-photon absorption. We find that two-photon electronic transitions of H 2 SO 4 are not a significant mechanism in the photodissociation of H 2 SO 4 .

Local modes of vibration have been clearly identified in infrared absorption, but sofar not in other kinds of optical spectroscopy. We have investigated the reason for this through model calculations on a simple, but realistic, double Morse oscillator model of the stretch vibrations of a CH 2 radical, excited by various optical processes involving a change of electronic state. The general result is, that the resulting spectrum is determined mainly by the excitation operator, and is normal-mode-like for excitation processes dominated by Franck-Condon factors. The specific form of the spectrum depends on the details of the excitation operator, and we investigate how the characteristics of the normal-mode-like spectrum depend on the difference in the equilibrium distance of the two potential surfaces.