Abstract For million years resin exudates have undergone chemical alterations by heat, pressure, radiation, water, oxygen, microorganisms, and have suffered processes of sedimentation and diagenesis. These agents have affected the organic functional groups present in the terpenes of the resins, giving rise to what we nowadays know as fossil resins. In this work, we try to get further insight in the chemical formation of fossil resins. As the simulation of the natural process is quite complex, we have focused on the temperature induced reactivity of the trans-communic acid, the main component of the Class I resins. Using this terpene derivate as a very basic model of a resin exudate, we have monitored their thermal changes by infrared spectroscopy, Differential Scanning Calorimetry and Thermogravimetric Analysis within the range of 25 to 340 °C. The temperature-induced transformation, both in presence and absence of inert atmosphere, is discussed on the basis of the reactivity of the conjugated double-bond, the exocyclic bond and the carboxylic acid group present in the trans-communic acid. The results obtained in these series of experiments agree with the maturation scheme accepted in the literature for natural resins, i.e. an initial cross-linked polymerization and a subsequent maturation reaction. From combined DSC/TGA and infrared spectroscopy results, we conclude that chemical changes produced in the trans-communic acid in the range 130–175 °C may mimic the initial polymerization-like process in the natural resins, whereas those produced between 180 and 340 °C seem to correspond to the maturation pathways described in the literature for fossil resins Class Ib. Spectral assignment of the most relevant infrared-active modes of the trans-communic acid at 25 °C is also provided with the aid of Density Functional Theory calculations.

中文翻译：

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以反式通讯酸为前驱体随温度形成化石树脂类似物的红外光谱研究

摘要 数百万年来，树脂渗出液在热、压、辐射、水、氧、微生物的作用下发生了化学变化，经历了沉积和成岩过程。这些试剂影响了树脂萜烯中存在的有机官能团，从而产生了我们现在所知的化石树脂。在这项工作中，我们试图进一步了解化石树脂的化学形成。由于自然过程的模拟非常复杂，我们重点研究了 I 类树脂的主要成分反式社区酸的温度诱导反应性。使用这种萜烯衍生物作为树脂渗出液的基本模型，我们通过红外光谱、差示扫描量热法和热重分析监测了它们在 25 至 340 °C 范围内的热变化。在存在和不存在惰性气氛的情况下，温度诱导的转变是基于共轭双键、环外键和反式市售酸中存在的羧酸基团的反应性来讨论的。在这一系列实验中获得的结果与文献中接受的天然树脂的熟化方案一致，即初始交联聚合和随后的熟化反应。从组合的 DSC/TGA 和红外光谱结果中，我们得出结论，反式公共酸在 130-175°C 范围内产生的化学变化可能模拟天然树脂中的初始聚合过程，而那些在 180-340°C 之间产生的化学变化°C 似乎对应于文献中描述的 Ib 类化石树脂的成熟途径。