How Well Can Theory Predict Addition - Fragmentation Equilibrium Constants in RAFT Polymerization?

2009 ◽  
Vol 62 (11) ◽  
pp. 1479 ◽  
Author(s):  
Ching Yeh Lin ◽  
Michelle L. Coote
Keyword(s):  
Ab Initio ◽  
Chain Length ◽  
Methyl Acrylate ◽  
Raft Polymerization ◽  
Equilibrium Constants ◽  
Molecular Orbital Calculations ◽  
Related System ◽  
Order Of Magnitude ◽  
Good Order ◽  
High Level

High level ab initio molecular orbital calculations are used to study the addition–fragmentation equilibrium constants of S-S’-bis(methyl-2-propionate)-trithiocarbonate mediated polymerization of methyl acrylate in toluene at –30°C. The results, which show strong solvent and chain length effects, are in good order of magnitude agreement with recent experimental results for a closely related system.

An Ab Initio Investigation of the Chain-Length Dependence of the Addition–Fragmentation Equilibria in RAFT Polymerization

2011 ◽  
Vol 64 (6) ◽  
pp. 747 ◽  
Author(s):  
Ching Yeh Lin ◽  
Michelle L. Coote
Keyword(s):  
Hydrogen Bonding ◽  
Ab Initio ◽  
Chain Length ◽  
Raft Polymerization ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Orbital Theory ◽  
Reversible Addition ◽  
Raft Agent ◽  
Length Effects

Ab initio molecular orbital theory has been used to study and explain the effects of chain length on the addition–fragmentation equilibrium constant in reversible addition–fragmentation chain transfer (RAFT) polymerization. New data is presented for azobisisobutyronitrile-initiated t-butyl dithiobenzoate-mediated polymerization of methyl methacrylate, and 2-(((ethylthio)carbonothioyl)thio)propanoic acid-mediated polymerization of acrylamide, and compared with published results for a dithiobenzoate-mediated polymerization of styrene and a trithiocarbonate-mediated polymerization of methyl acrylate. The effects of primary and penultimate substituents on the addition–fragmentation equilibrium constants in RAFT polymerization can be very large (up to eight orders and four orders of magnitude respectively) and should be taken into account in kinetic models. Antepenultimate unit effects are relatively small, implying that, for most systems, chain length effects have largely converged by the dimer stage. However, for sterically bulky monomers capable of undergoing anchimeric interactions such as hydrogen bonding, the onset and convergence of these substituent effects is delayed to slightly longer chain lengths. The magnitude and direction of chain-length effects in the addition–fragmentation equilibrium constants varies considerably with the nature of the RAFT agent, the initiating species, the propagating radical, and the solvent. The observed substituent effects arise primarily in the differing stabilities of the attacking radicals, but are further modified by homoanomeric effects and, where possible, hydrogen-bonding interactions.

Ab initio Molecular Orbital Calculations of Reduced Partition Function Ratios of Polyboric Acids and Polyborate Anions

2000 ◽  
Vol 55 (6-7) ◽  
pp. 623-628 ◽  
Author(s):  
Takao Oi
Keyword(s):  
Partition Function ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Equilibrium Constants ◽  
Boron Isotope ◽  
Molecular Orbital Calculations ◽  
Exact Evaluation ◽  
Reac Tions

Abstract Molecular orbital calculations at the HF/6-3 lG(d) level were carried out for polyboric acids and poly-borate anions up to a pentamer to estimate their 11B -to-10B isotopic reduced partition function ratios (RPFRs) and examine the additivity of logarithms of RPFRs. Approximate RPFR-values calculated by the use of the additivity agreed with exact RPFR-values within a margin of 1% error. This error was equivalent to a 5% error on ln(RPFR). The equilibrium constants of mono boron isotope exhange reac-tions between three-coordinate boron and four-coordinate boron ranged from 1.0203 to 1.0360 at 25 °C, indicating the importance of exact evaluation of RPFRs of polymers.

Analysis of molecular polarizabilities and polarizability derivatives in H2, N2, F2, CO, and HF, with the theory of atoms in molecules

1996 ◽  
Vol 74 (6) ◽  
pp. 1139-1144 ◽  
Author(s):  
Kathleen M. Gough ◽  
Margaret M. Yacowar ◽  
Richard H. Cleve ◽  
Jason R. Dwyer
Keyword(s):  
Charge Transfer ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Atoms In Molecules ◽  
Molecular Polarizability ◽  
Molecular Orbital Calculations ◽  
Induced Dipole ◽  
Order Of Magnitude ◽  
Atomic Dipole ◽  
Molecular Polarizabilities

Ab initio molecular orbital calculations have been performed on the title molecules at the SCF-HF and MP2 levels to obtain molecular polarizabilities and the derivatives associated with bond stretch. The wave functions from these calculations have been analyzed with the theory of atoms in molecules (AIM). Both the polarizability and its derivative are successfully reconstructed from AIM terms representing the transfer of charge between atoms (CT = charge transfer) and the rearrangement of charge within an atomic basin (AD = atomic dipole). The results for the diatomics are compared to each other and to the alkanes studied previously. Equilibrium polarizabilities are qualitatively explained with reference to atomic electronegativity and type of bonding. While derivatives of the mean molecular polarizability differ by a factor of two at most, individual contributions vary by an order of magnitude. The derivatives along the bond axis for H2 are ΔCT = 2.06 and ΔAD = −0.62 × 10−30 C m/V, while for N2 they are ΔCT = 13.77 and ΔAD = −10.00 × 10−30 C m/V. The common feature observed is that as the induced dipole due to charge transfer increases, the induced dipole due to changes in the atomic dipole also increases and opposes it. Key words: diatomic molecules, molecular polarizability, molecular polarizability derivative, theory of atoms in molecules, ab initio molecular orbital calculations.

scholarly journals Nuclear Quadrupole Coupling in 5-Membered Ring Oxygen and Sulphur Heterocyclic Compounds; Studies by Nuclear Quadrupole Resonance and Ab Initio Molecular Orbital Calculations

1979 ◽  
Vol 34 (2) ◽  
pp. 220-232 ◽  
Author(s):  
Mavis Redshaw ◽  
Michael H. Palmer ◽  
Robert H. Findlay
Keyword(s):  
Ab Initio ◽  
Nuclear Quadrupole Resonance ◽  
Principal Axis ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Quadrupole Coupling ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole ◽  
High Level ◽  
Level Of Agreement

Abstract The 14N nuclear quadrupole resonance spectra for the compounds 2a, b, 3b, 4b, 5a, b, 6b have been obtained at 77 K and the asymmetry parameter and coupling constants extracted. A comparison of these with microwave spectral results, shows that small but systematic differences occur between the solid and gaseous states. There is a high level of agreement for the observed coupling constants from NQR or MW spectra and the ab initio calculations in both magnitude and direction. This enables us to extract further principal axis data from the observed microwave spectra, and to predict with some confidence the axes and coupling magnitudes for other members of the series where incomplete determinations are available. Variations in coupling constants with structure are discussed

Photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction, Part 12. Factors controlling the regiochemistry of the reaction with alcohol as the nucleophile

1996 ◽  
Vol 74 (11) ◽  
pp. 2143-2166 ◽  
Author(s):  
Donald R. Arnold ◽  
Mary S. W. Chan ◽  
Kimberly A. McManus
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Radical Cations ◽  
Major Product ◽  
Convincing Evidence ◽  
Molecular Orbital Calculations ◽  
Aromatic Substitution ◽  
Intermediate Radical ◽  
High Level ◽  
Allylic Radical

The photo-NOCAS reaction that combines methanol, serving as the nucleophile, and the radical cation of 4-methyl-1,3-pentadiene (14+•), substituting on the 1,4-dicyanobenzene radical anion (1−•), yields (E)-1-(4-cyanophenyl)-4-methoxy-4-methyl-2-pentene (15) as the major product. This regioisomer arises from bonding of methanol to C-4, the more heavily alkyl-substituted carbon of the diene, giving the less alkyl-substituted allylic radical. All previous examples of the photo-NOCAS reaction have yielded major adduct(s) having regiochemistry consistent with the anti-Markovnikov rule; the more heavily substituted (more stable?) β-alkoxyalkyl radical was the predominant intermediate. Empirically derived heats of formation and high-level ab initio molecular orbital calculations (MP2/6-31G*//HF/6-31G*) provide convincing evidence that of the two alternative allylic radicals, generated upon addition of methanol to 14+•, that which has the more alkyl substituted allylic radical moiety is, in fact, not the more stable. Of course, the total structure of the intermediate must be considered; the stabilizing effect of alkyl substitution on the carbon next to the oxygen of the ether moiety cannot be ignored. Ab initio molecular orbital calculations (MP2/6-31G*//HF/6-31G*) are reported for the radical cations of 2-methylpropene (2+•), 2-methyl-2-butene (6+•), 2-methyl-1,3-butadiene (9+•), 4-methyl-1,3-pentadiene (14+•), and 2,4-dimethyl-1,3-pentadiene (18+•) Calculations were also carried out on possible intermediates (bridged radical cations, distonic radical cations, and β-alkoxyalkyl radicals) involved upon reaction of these radical cations with methanol. Results of these calculations provide a basis for explaining/predicting the regiochemistry of the photo-NOCAS reaction involving methanol as the nucleophile: the major adduct(s) result(s) from attachment of methanol to that end of the alkene or diene which gives rise to the more stable intermediate radical. The more stable radical is not necessarily the more heavily alkyl substituted. Key words: photoinduced electron transfer, radicals, radical cations, ab initio molecular orbital calculations.

Ab Initio Kinetic Modelling in Radical Polymerization: A Paradigm Shift in Reaction Kinetic Analysis

2006 ◽  
Vol 59 (10) ◽  
pp. 712 ◽  
Author(s):  
Michelle L. Coote ◽  
Christopher Barner-Kowollik
Keyword(s):  
Kinetic Model ◽  
Ab Initio ◽  
Kinetic Modelling ◽  
Raft Polymerization ◽  
Reaction Scheme ◽  
Rate Coefficients ◽  
Macroscopic Properties ◽  
Potential Applications ◽  
The Individual ◽  
High Level

We describe a new rationale to kinetic modelling in which adjustable parameters are avoided through the use of quantum chemistry. This new approach reverses the standard modelling approach in which, having first assumed a kinetic model, it is then fitted to the experimentally determined values of the macroscopic properties (rates, compositions, molecular weight distributions, and so forth) so as to estimate the rate coefficients of the individual reactions. Instead, one still assumes a reaction scheme, but then calculates the rates of the individual reactions using high-level ab initio calculations, and in this way a kinetic model is built that can be used to predict the macroscopic properties of the process from first principles. These can then be compared directly with experiment (for benchmarking purposes) and subsequently be employed to predict the outcome of new chemical processes. In here we illustrate the ab initio modelling technique, using a recent study of initialization in RAFT polymerization as a case study. We also discuss its advantages and possible problems, and highlight some of its potential applications in the radical polymer field.

Configurational Assignment and Conformational Study of Methylglyoxal Bisdimethylhydrazones Derived from the 2-Ethoxypropenal Precursor

2006 ◽  
Vol 59 (3) ◽  
pp. 211 ◽  
Author(s):  
Leonid B. Krivdin ◽  
Lyudmila I. Larina ◽  
Kirill A. Chernyshev ◽  
Natalia A. Keiko
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Experimental Measurements ◽  
Conformational Study ◽  
Lone Pairs ◽  
Configurational Assignment ◽  
Out Of Plane ◽  
High Level

A configurational assignment of the isomeric methylglyoxal bisdimethylhydrazones derived from the 2-ethoxypropenal precursor has been performed based on experimental measurements and high-level ab initio calculations of 1J(C,C) and 1J(C,H) couplings. The results reveal the marked stereochemical dependence upon the orientation of the lone pairs of both nitrogen atoms in different isomers. Methylglyoxal bisdimethylhydrazone is shown to exist in a mixture of the EE and ZE isomers (ca. 75:25), both of which adopt predominant s-trans conformations with minor (up to 8°) out-of-plane deviations.

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