The application of molecular orbital calculations to wood chemistry

Elder, Thomas; Worley, S. D.

doi:10.1007/bf00353367

Cited by 16 publications

(17 citation statements)

References 11 publications

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“…conformer I of the β-O-4 DHDLs corresponds to dehydrogenation of conformer I of the β-O-4 dilignols presented by Durbeej and Eriksson (2003) etc. The calculations by Elder and Worley (1984) showed that the atomic sites having most of the unpaired spin actually are those through which polymerization occurs, and that the spin densities of the atomic sites within the aromatic ring are higher than that of the phenolic oxy-gen. Our study verifies that the unpaired spin of the coniferyl alcohol radical exists primarily on atoms involved in bond formation during polymerization, but assigns the highest spin to the O-4 position (i.e. This odd-alternant pattern with negative spins at those particular positions is a well-characterized feature of phenyl radicals, and has been reproduced in, e.g., density functional theory studies on the tyrosyl radical (Himo et al , 1999.…”

Section: Resultsmentioning

confidence: 99%

“…1). This hypothesis, which below will be referred to as the spin distribution hypothesis, was later tested by Elder and Worley (1984), and subsequently revisited by Elder and Ede (1995). kinetically controlled) by the 3-hydroxy-propen-1-yl-and the methoxy group, respectively, these researchers furthermore argued that the phenoxy radical electron distribution would account for the fact that β-5, β-β, β-O-4, and 5-5 are the major oxidative dimerization products (dilignols) observed in experimental studies.…”

Section: Introductionmentioning

confidence: 99%

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Spin Distribution in Dehydrogenated Coniferyl Alcohol and Associated Dilignol Radicals

Durbeej¹,

Eriksson²

2003

Holzforschung

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spin Distribution in Dehydrogenated Coniferyl Alcohol and Associated Dilignol Radicals

Durbeej¹,

Eriksson²

2003

Holzforschung

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“…Crystal structures have shown that syringyl-type groups have methoxyl torsion angles of 220" to the ring for one group and at about 85" for the second methoxyl group (27). Molecular mechanics Rotation at the P-0-4 bond (36) and molecular orbital studies (37) also have found similar The two torsion angles at the P-0-4 bond between rings B and dihedral angles for the methoxyl groups. For the three C3 C have the greatest rotation barriers as shown by the results methoxyls we have calculated minimum torsion angles (CMe0-presented in Figs.…”

Section: Methoxyl Rotationmentioning

confidence: 91%

Conformational analysis and 2D NMR assignment strategies for lignin model compounds. The structure of acetoguaiacyl-dehydro-diisoeugenol methyl ether

Garver¹,

Maa²,

Marat³

1996

Can. J. Chem.

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Abstract:The resolved 'H and I3c chemical shifts for the lignin model trimer acetoguaiacyl-dehydro-diisoeugenol methyl ether have been completely assigned using one-and two-dimensional NMR techniques. Identification of spin families and assignments within the spin families were made using routine one-dimensional experiments for chemical shifts and multiplicities, and COSY and heteronuclear correlation experiments to determine connectivities. NOESY, HOESY, and longrange heteronuclear correlation experiments were then used to determine the juxtaposition of the assigned groups and to provide a confirmation of assignments. Steady state NOE difference and time-dependent NOESY and HOESY experiments were then used to provide experimental measures of the trimer conformation. Semiempirical molecular orbital methods were used to calculate minimum energy structures and energy barriers for bond rotations within the molecule. We have found that for the trimer-size molecule the NOE experiments provide a less detailed picture of the molecular conformation than the molecular orbital results. A comparison of NOE and M O results with crystal structures from the literature indicates the extent to which sidechain and methoxyl torsion angles may be estimated using each method. The correlation between NOE and MO predictions for interatomic distances apparently is related to the narrow minima for P-0-4 torsion angles for which the different results confirm each other. Broad minima or low-energy barriers for torsion angle rotations may yield minimized structures by computational methods that are not experimentally justified.Key words: semiempirical molecular orbital calculation, 2D NMR, conformation, lignin model, nuclear Overhauser effect. On a trouvk que pour la molkcule de la grosseur d'un trimkre, les expkriences d'eOn fournissent une reprksentation moins dCtaillee de la conformation de la molkcule que les rksultats d'orbitales molkculaires. Une comparaison des rksultats des e o n et des calculs d'OM avec les structures cristallines obtenues h partir de la IittCrature indiquent que l'on peut kvaluer les angles de torsion entre la chaine latkrale et le mkthoxyle. La corrklation entre les prkdictions faites sur la base des e o n et des calculs d'OM pour les distances interatomiques est apparemment relite au fait que les minima pour les angles de torsion du P-0-4 pour lesquels les diffkrents rksultats se confirment mutuellement sont Ctroits. Des barri6res aux rotations des angles de torsion qui seraient larges ou faibles peuvent conduire h des structures minimiskes par des mCthodes de calculs qui ne sont pas justifiCes exptrimentalement. RCsumC Mots ~1 6 .~: calculs semiempiriques d'orbitales molkculaires, RMN 3D, conformation, modkle pour la lignine, effet Overhauser nucltaire.[Traduit par la redaction] I

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“…An early hypothesis was that the linkage ratios should be related to spin density at the various positions on the molecule. A more sophisticated analysis was used by Elder and Worley (1984) to test this hypothesis. The conclusion that spin density was the determining factor was reasonable because, as expected, the dominant linkages observed were the b-b, b-O-4, b-5, and 5-5 linkages.…”

Section: Previous Workmentioning

confidence: 99%

What Factors Control Dimerization of Coniferyl Alcohol?

Houtman¹

1999

Holzforschung

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Data suggest that the dimerization of coniferyl alcohol is not under thermodynamic control. In this study, molecular dynamics calculations were used to estimate the effect of the solvent environment. In water, the coniferyl alcohol radicals were forced to associate by the formation of a solvent cage. In glycerol, the solvent cage effect appeared to be absent. These results suggest that in water, the product distribution of the dimers will be modified by interactions with the solvent. The computed results are consistent with experimental observations of coniferyl alcohol reactions in various solvents.

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The application of molecular orbital calculations to wood chemistry

Cited by 16 publications

References 11 publications

Spin Distribution in Dehydrogenated Coniferyl Alcohol and Associated Dilignol Radicals

Spin Distribution in Dehydrogenated Coniferyl Alcohol and Associated Dilignol Radicals

Conformational analysis and 2D NMR assignment strategies for lignin model compounds. The structure of acetoguaiacyl-dehydro-diisoeugenol methyl ether

What Factors Control Dimerization of Coniferyl Alcohol?

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