背景:羰基化合物,尤其是醛,排放到大气中,可能遭受气溶胶或云层中水滴的水合作用。同时,它们可以与羟基自由基反应,羟基自由基可以从这些物种中添加或提取氢原子。使用密度泛函和量子复合理论方法研究了水合与氢提取之间的相互作用,在气相和模拟散装水中。从甲醛的醛和二元醇形式中提取H,乙醛,乙醇醛,乙二醛,甲基乙二醛,和丙烯醛进行了研究,以确定取代基对一种形式或另一种形式的抽象的偏好是否有任何明显的影响。发现在甲醛的情况下,与羰基相邻的H原子的提取比从双元二醇的相同提取产生更稳定的自由基,乙醛,和乙醇醛。在Cα中存在离域基团(乙二醛和甲基乙二醛中的羰基,和丙烯醛中的乙烯基),扭转了这种趋势,现在从双元二醇中提取H原子会产生更稳定的自由基。进行了进一步的研究,从所考虑的物种中的其他不同位置提取氢原子,醛和双元二醇形式。只有在乙醇醛的情况下,通过从-CH2OH基团提取H形成的自由基比任何其他自由基物种更稳定。对二元醇中的一个羟基中的氢原子的提取等同于向醛中添加·OH基团。它导致了,在某些情况下,分解成一个较小的自由基和一个中性分子。在这些情况下,在气相和(模拟)本体溶剂中的结果之间观察到一些有趣的理论差异,以及所选择的计算方法。
方法:DFT(M06-2X,B2PLYP,PW6B95),CCSD(T),和复合材料(CBS-QB3,Jun-ChS,SCVECV-f12)使用Dunning基集和外推至CBS极限的方法来研究酮基和二元醇形式的闭壳醛的能量学,以及通过氢提取从它们衍生的自由基。进行了气相和模拟本体溶剂计算,在最后一种情况下使用可极化连续体模型。
BACKGROUND: Carbonyl compounds, especially aldehydes, emitted to the atmosphere, may suffer hydration in aerosols or water droplets in clouds. At the same time, they can react with hydroxyl radicals which may add or abstract hydrogen atoms from these species. The interplay between hydration and hydrogen abstraction is studied using density functional and quantum composite theoretical methods, both in the gas phase and in simulated bulk water. The H-abstraction from the aldehydic and geminal diol forms of formaldehyde, acetaldehyde, glycolaldehyde,
glyoxal, methylglyoxal, and acrolein is studied to determine whether the substituent has any noticeable effect in the preference for the abstraction of one form or another. It is found that abstraction of the H-atom adjacent to the carbonyl group gives a more stable radical than same abstraction from the geminal diol in the case of formaldehyde, acetaldehyde, and glycolaldehyde. The presence of a delocalizing group in the Cα (a carbonyl group in
glyoxal and methylglyoxal, and a vinyl group in acrolein), reverts this trend, and now the abstraction of the H-atom from the geminal diol gives more stable radicals. A further study was conducted abstracting hydrogen atoms from the other different positions in the species considered, both in the aldehydic and geminal diol forms. Only in the case of glycolaldehyde, the radical formed by H-abstraction from the -CH2OH group is more stable than any of the other radical species. Abstraction of the hydrogen atom in one of the hydroxyl groups in the geminal diol is equivalent to the addition of the •OH radical to the aldehyde. It leads, in some cases, to decomposition into a smaller radical and a neutral molecule. In these cases, some interesting theoretical differences are observed between the results in gas phase and (simulated) bulk solvent, as well as with respect to the method of calculation chosen.
METHODS: DFT (M06-2X, B2PLYP, PW6B95), CCSD(T), and composite (CBS-QB3, jun-ChS, SCVECV-f12) methods using Dunning basis sets and extrapolation to the CBS limit were used to study the energetics of closed shell aldehydes in their keto and geminal-diol forms, as well as the radical derived from them by hydrogen abstraction. Both gas phase and simulated bulk solvent calculations were performed, in the last case using the Polarizable Continuum Model.