β-O-4型木质素二聚体中键离解能的理论计算

Theoretical Calculation of Bond Dissociation Energies for β-O-4 Linkage Lignin Dimer

采用密度泛函理论B3LYP方法,在6-31G(d,p)基组水平上对5种β-O-4型木质素二聚体的醚键和C-C键的键离解能进行了理论计算与分析。计算结果表明,各种键离解能中,Cβ-O键的离解能最小,其次是Cα-Cβ键,各键离解能的大小顺序为:Cβ-O<Cα-Cβ<Caromatic-O<Caromatic-Cα。模化物1上氢原子被取代基(甲氧基、羟甲基、甲基或羟基)取代后的衍生物的Cβ-O和Cα-Cβ键的键离解能有所降低,而Caromatic-O和Caromatic-Cα键的键离解能变化不大。在木质素的热解过程中,Cβ-O键优先断裂,是热解引发键,Cα-Cβ键的断裂是一条主要的竞争路径。

The C-O and C-C bond dissociation energies for five β-O-4 linkage lignin dimer were theoretically cal culated by using density functional theory methods B3LYP at 6-31G（d,p） level.The calculation results show that the bond dissociation energy of Cβ-O is the lowest,and that of Cα-Cβ is second lowest,and the order of all kinds of bond dissociation energy is Cβ-O 〈 Cα-Cβ 〈 Caromatic-O 〈 Caromatic-Cα.The substituent group （methoxyl,hydroxymethyl,methyl and hydroxyl） on model compound 1 can lower the Cβ-O and Cα-Cβbond dissociation energies,but the Caromatic-O and Caromatic-Cα bond dissociation energies change little.In pyrolysis processes of lignin,the homolytic cleavage of Cβ-O bond is the initial step,and Cα-Cβ bond cleavage is a competitive reaction path.