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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Molecular Energetics of Cytosine Revisited: A Joint Computational and Experimental Study
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Molecular Energetics of Cytosine Revisited: A Joint Computational and Experimental Study

机译：重述胞嘧啶分子的能量学：联合计算和实验研究。

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A static bomb calorimeter has been used to measure the standard molar energy of combustion, in oxygen, at T = 298.15 K, of a commercial sample of cytosine. From this energy, the standard (p = 0.1 MPa) molar enthalpy of formation in the crystalline state was derived as -(221.9 ± 1.7) kJ·mol~(-1). This value confirms one experimental value already published in the literature but differs from another literature value by 13.5 kJ·mol~(-1). Using the present standard molar enthalpy of formation in the condensed phase and the enthalpy of sublimation due to Burkinshaw and Mortimer [J. Chem. Soc., Dalton Trans. 1984, 75], (155.0 ± 3.0) kJ·mol~(-1), results in a value for the gas-phase standard molar enthalpy of formation for cytosine of -66.9 kJ·mol~(-1). A similar value, -65.1 kJ·mol~(-1), has been estimated after G3MP2B3 calculations combined with the reaction of atomization on three different tautomers of cytosine. In agreement with experimental evidence, the hydroxy-amino tautomer is the most stable form of cytosine in the gas phase. The enthalpies of formation of the other two tautomers were also estimated as -60.7 kJ·mol~(-1) and -57.2 kJ·mol~(-1) for the oxo-amino and oxo-imino tautomers, respectively. The same composite approach was also used to compute other thermochemical data, which is difficult to be measured experimentally, such as C-H, N-H, and O-H bond dissociation enthalpies, gas-phase acidities, and ionization enthalpies.
机译：静态炸弹量热仪已用于测量商业上的胞嘧啶样品在T = 298.15 K时在氧气中燃烧的标准燃烧摩尔能。根据该能量，在结晶状态下形成的标准（p = 0.1 MPa）摩尔焓为-（221.9±1.7）kJ·mol〜（-1）。该值证实了一个已经在文献中发表的实验值，但与另一个文献值相差13.5 kJ·mol〜（-1）。使用目前的标准冷凝相生成摩尔焓和因Burkinshaw和Mortimer引起的升华焓[J．化学道尔顿Trans。 1984，75]，（155.0±3.0）kJ·mol〜（-1），胞嘧啶的气相标准摩尔形成焓值为-66.9 kJ·mol〜（-1）。在计算了G3MP2B3并结合了三种不同胞嘧啶互变异构体的雾化反应后，估计出相似的值-65.1 kJ·mol〜（-1）。与实验证据一致，羟基-氨基互变异构体是气相中胞嘧啶的最稳定形式。对于氧-氨基和氧-亚氨基互变异构体，另外两个互变异构体的形成焓也分别估计为-60.7 kJ·mol〜（-1）和-57.2 kJ·mol〜（-1）。相同的复合方法还用于计算其他热化学数据，这些数据很难通过实验进行测量，例如C-H，N-H和O-H键解离焓，气相酸度和电离焓。

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