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Cyclopropane rings are versatile building blocks in organic chemistry. Their synthesis, by the reaction of sulfur ylides with α,β-unsaturated carbonyl compounds, has recently aroused renewed interest after the discovery of efficient catalysis by using (S)-indoline-2-carboxylic acid. In order to rationalize the behavior of this catalyst, MacMillan proposed a directed electrostatic activation (DEA) mechanism, in which the negative carboxylate group interacts with the positive thionium moiety, thus reducing the activation energy and increasing the reaction rate. More recently, Mayr refuted some of MacMillan conclusions, but accepted the DEA mechanism as a justification for the experimental high reaction rates. In contrast, our results indicate that the selectivity obtained in the process seems to result from several strong hydrogen bond interactions between the two reacting species, while no strong evidence for a DEA mechanism was found. We also concluded that the hydrogen bonds don't improve the reaction rate by lowering the activation energy of the rate-determining step, but can do it by promoting efficient reaction trajectories due to long-range complexation of the reagents. Finally, our results confirm that the cyclopropanation reaction occurs by a two-step mechanism, and that the overall enantioselectivity depends on the relative energies of the two steps, averaged by the relative populations of the iminium intermediates that are initially formed in the reaction.

The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is α,β-conjugated, as in acrylic esters or acrylamides. Additions at the α- and β-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions.

The values of combustion and formation enthalpy for glycolic acid (I) and glycolide (II) were determined by calorimetry. The temperature dependence of vapor pressures of I and II was obtained using the transpiration method, and the sublimation enthalpies were obtained. The enthalpy of melting of I was found by differential scanning calorimetry. Stable conformers were determined by the ab initio (DFT) method, and combinations of the fundamental oscillations and inertia momenta of I and II conformers were calculated. The full and relative energies of the compounds most stable conformers were found by a composite G3MP2 method, and the enthalpies of formation of I and II in the gaseous state were estimated. The values of the thermodynamic properties in the ideal gas state were determined over the range of 0–1500 K. A thermodynamic analysis was performed for the process of preparation of II from I and the formation of polyglycolide (III) from I and II.

The enthalpies of combustion and formation of S-lactic acid at 298.15 K, ΔcHmo(cr.) = −1337.9 ± 0.8 and ΔfHmo(cr.) = −700.1 ± 0.9 kJ/mol, were determined by calorimetry. The temperature dependence of acid vapor pressure was studied by the transpiration method, and the enthalpy of its vaporization was obtained, ΔvapHo(298.15 K) = 69.1 ± 1.0 kJ/mol. The temperature and enthalpy of fusion, Tm (330.4 K) and ΔmHo(298.15 K) = 14.7 ± 0.2 kJ/mol, were determined by differential scanning calorimetry. The enthalpy of formation of the acid in the gas phase was obtained. Ab initio methods were used to perform a conformational analysis of the acid, calculate fundamental vibration frequencies, moments of inertia, and total and relative energies of the stablest conformers. Thermodynamic properties were calculated in the ideal gas state over the temperature range 0–1500 K. A thermodynamic analysis of mutual transformation processes (the formation of SS- and RS(meso)-lactides from S-lactic acid and the racemization of these lactides) and the formation of poly-(RS)-lactide from S-lactic acid and SS- and RS(meso)-lactides was performed.

The values of the combustion and enthalpies of formation for e-caprolactone were determined by means of combustion calorimetry. The vapor pressures of lactone were measured in the range of 283–353 K, and the value of its enthalpy of vaporization was estimated by the transpiration method. Conformational analysis and calculations of the equilibrium structures, inertia moments, and sets of fundamental vibrations was performed by the B3LYP/6-311++G(3 df, 3 pd) quantum-chemical method. The total energies of the most stable lactone conformers were found and ΔfH(g) was estimated using the composite G3MP2 method. The set of fundamental vibrations for the most stable conformers of the compound was developed on the basis of the available experimental IR spectra and calculated vibration frequencies. The values of the thermodynamic properties of e-caprolactone were determined in the ideal ga s state in the range of 0—1500 K. A set of reliable and interconsistent thermodynamic parameters for e-caprolactone was created. Thermodynamic analysis for liquid-phase polymerization of s-caprolactone in the temperature range of 220—500 K was carried out.

In this work, we performed a complex study of the thermodynamic properties of three alkylated γ -lac- tones. We determined their enthalpies of combustion and formation, measured vapor pressures and found the enthalpies of vaporization, and studied their conforma- tional state. The spectral and molecular data were used to calculate the thermodynamic properties of γ -pen- tanolactone ( I ), γ -hexanolactone ( II ), and γ -nonanolac- tone ( III ). Abstract —The enthalpies of formation of γ -pentanolactone ( I ), γ -hexanolactone ( II ), and γ -nonanolactone ( III ) were determined by combustion calorimetry. The enthalpies of vaporization of these lactones were mea- sured by the transfer method. Conformational analysis was performed and equilibrium structures, sets of fun- damental vibrations, moments of inertia, and total energies of the stablest conformers of I , II , and III were cal- culated by the B3LYP/6-311G( d , p ) , G3MP2, and CBS-QB3 methods. The experimental IR spectra and calcu- lated vibrational frequencies were used to obtain sets of fundamental vibrations of the stablest conformations. The thermodynamic properties of I - III in the ideal gas state were determined over the temperature range 0- 1500 K. Additive and quantum-chemical methods were applied to estimate the ∆ f H ° (g) values of a number of γ -lactones. Composite quantum-chemical methods were used to obtain the energies of monomethyl γ -butyro- lactones and estimate their relative stability depending on the position of the methyl substituent in the ring.

The enthalpies of formation of δ-hexanolactone and δ-nonanolactone were determined by combustion calorimetry. Conformational analysis and quantum-chemical calculations of equilibrium structures, fundamental vibrations, moments of inertia, and total energies were performed for δ-pentanolactone (I), δ-hexanolactone (II), and δ-nonanolactone (III) by the B3LYP/6-311G(d,p), B3LYP/6-311++G(d,p), and G3MP2 methods. The experimental IR spectra and calculated vibrational frequencies were used to suggest the assignment of vibrational frequencies of stable conformations. The thermodynamic properties of I–III in the ideal gas state were determined over the temperature range 0–1500 K. A thermodynamic analysis of mutual isomerization in the gas and liquid phases over the temperature range 298.15–900 K and liquid-phase polymerization of γ- and δ-pentanolactones and 4-pentenoic acid over the temperature range 298.15–500 K was performed.

The enthalpy of formation of liquid 4-pentenoic acid was determined by combustion calorimetry. The vapor pressure and enthalpy of vaporization of the compound were measured by the transfer method over the temperature range 289-324 K. Conformational analysis was performed. The equilibrium structure, funda- mental vibrations, moments of inertia, and total energy of the stablest acid conformers were calculated by the B3LYP/6-311G( d , p ) and G3MP2 quantum-chemical methods. The experimental IR spectrum and calculated vibrational frequencies were used to assign IR bands. The thermodynamic properties of monomeric 4-pentenoic acid in the ideal gas state were calculated over the temperature range 0-1500 K. Additive and quantum-chem- ical methods were used to estimate the ∆ f H ° (g) and ∆ vap H ° values. Close agreement between the calculation results and experimental data was obtained. It was shown that additive and quantum-chemical methods could be used for estimating the enthalpies of formation and vaporization of nonconjugated alkenoic acids.

The infrared (IR) spectra of sulfanilamide 1 and of its azanion (counter ion Na+) 2 have been measured in dimethyl sulfoxide (DMSO) solutions. The density functional theory (DFT) B3LYP 6-31++G(d,p) computations performed adequately describe the experimental spectroscopic data, including the corresponding frequency isotopic shifts. In agreement between theory and experiment, the conversion of sulfanilamide 1 into azanion 2 results in strong frequency decreases of the asymmetrical and symmetrical vibrations of the SO2 group: predicted 122 cm−1, measured 140 cm−1 in solution (total values), as well as in other essential IR spectral changes. According to the computations, the strongest changes in the steric structure take place at and next to the azanionic center. The new (azanionic) charge is distributed, as follows: 0.08e−, 0.23e−, and 0.12e− are delocalized over the amino, phenylene, and sulfonic groups, respectively, and 0.57e− of it remain localized at the azanionic center. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

The structure and infrared spectra of formonitrile (hydrogen cyanide) and acetonitrile, their anions, and radicals (45 species in all) have been studied by density functional theory (DFT) B3LYP 6-31++G(d,p) calculations. The results obtained have been compared with the literature and original experimental data. The zero-point vibrational energy (ZPVE)-corrected deprotonation energies of the studied (and other) nitriles correlate fairly well (R = 0.94) with their pKa values, measured in dimethyl sulfoxide (DMSO). The theoretical cyano stretching frequencies νCN of the species studied have been found to correlate satisfactorily (R = 0.97) with the experimental ones. The latter correlation can be used for a theoretical estimation of νCN of many nitriles, their anions, and radicals. The geometry parameters for the molecules, calculated by the same theoretical method, practically coincide with those determined experimentally in the gas state. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

The synthesis of 3-amino-2-butenenitrile (diacetonitrile) by base-catalyzed dimerization of acetonitrile was followed by IR spectra, ab initio HF, MP2 and DFT BLYP, B3LYP force field calculations, and correlation analysis. The conversion of diacetonitrile into the anion causes a 67 cm −1 decrease in the cyano stretching frequency, a threefold increase in the corresponding integrated intensity and other strong spectral changes. In agreement between theory and experiment, the isomerization takes place in the intermediate − NC(CH 3 )CH 2 CN→[HNC(CH 3 )CHCN] − rather than in the end (protonation) product HNC(CH 3 )CH 2 CN→H 2 NC(CH 3 )CHCN, due to the essential energy difference between the charge-localized and delocalized anionic intermediates.