Dioxygen

    Dioxygen is obtained industrially by the liquefaction and fractional distillation of air, and is stored and transported as a liquid. Convenient laboratory preparations of O₂ are the electrolysis of aqueous alkali using Ni electrodes, and decomposition of H₂O₂ (equation 1.1). A mixture of KClO₃ and MnO₂ used to be sold as ‘oxygen mixture’ (equation 1.2) and the thermal decompositions of many other oxo salts (e.g. KNO₃, KMnO₄ and K₂S₂O₈) produce O₂.

         )         1.1(

                      (1.2(

    Dioxygen is a colourless gas, but condenses to a pale blue liquid or solid. and 1.13. In all phases, it is paramagnetic with a triplet ground state, i.e. the two unpaired electrons have the same spin, with the valence electron configuration being:

    In this state, O₂ is a powerful oxidizing agent  but, fortunately, the kinetic barrier is often high; if it were not, almost all organic chemistry would have to carried out in closed systems. However, asinglet state, O^2- , with a valence electron configuration of:

  lies only 95 kJ mol^-1 above the ground state. This excited state can be generated photochemically by irradiation of O₂ in the presence of an organic dye as sensitizer, or nonphotochemically by reactions such as 1.3.

                               (1.3)

    Singlet O₂ is short-lived, but extremely reactive, combining with many organic compounds, e.g. in  reaction 1.4, O^2- acts as a dienophile in a Diels–Alder reaction.

                                           (1.4)

      At high temperatures, O₂ combines with most elements, exceptions being the halogens and noble gases, and N₂ unless under special conditions. Reactions with the group 1 metals are of particular interest, oxides, peroxides, superoxides and suboxides being possible products. Bond lengths in O₂, [O₂]^-  and [O₂]^2-  are 121, 134 and 149pm , consistent with a weakening of the bond caused by increased occupation of the  π^* MOs.   The first ionization energy of O₂ is 1168 kJ mol^-1 and it may be oxidized by very powerful oxidizing agents such as  PtF6 (equation 1.5). The bond distance of 112pm in [O₂]⁺‏ is in keeping with the trend for O₂, [O₂]^- and [O₂]^2-. Other salts include [O₂]⁺‏‏[SbF₆]^- (made from irradiation of O₂ and F₂ in the presence of SbF₅, or from O₂F₂ and SbF₅) and [O₂]‏⁺‏[BF₄]^- (equation 1.6).

                                    (1.5)

             (1.6)

   The chemistry of O₂ is an enormous topic, and examples of its reactions can be found throughout this book.

مواضيع ذات صلة

كيمياء القصدير

تطبيقات الطبقات الثنائية الهيدروكسيد

تطبيقات عملية التبادل الأيوني

مواد التبادل الأيوني Ion exchanger

ظاهرة التبادل الايوني Ion Exchange

تاريخ التبادل الايوني Ion Exchange History

كيمياء البلاتين ومعقداته

كيمياء البلاديوم ومعقداته

طرائق تقدير النحاس

كيمياء النحاس ومعقداته

طرائق تقدير النيكل

كيمياء النيكل ومعقداته