Halogens as Lewis acids

Key point: Bromine and iodine molecules act as mild Lewis acids. Lewis acidity is expressed in an interesting and subtle way by Br₂ and I₂, which are both strongly coloured. The strong visible absorption spectra of Br₂ and I₂ arise from transitions to low-lying unfilled antibonding orbitals. The colours of the species therefore suggest that the empty orbitals may be low enough in energy to serve as acceptor orbitals in  

Figure 4.10 The interaction of Br2 with the carbonyl group of propanone. (a) The structure of (CH3 )2 COBr2 shown by X-ray diffraction. (b) The orbital overlap responsible for the complex formation. (c) A partial molecular orbital energy level diagram for the σ and σ* orbitals of Br₂ with the appropriate combinations of the sp² orbitals on the two O atoms. The charge transfer transition is labelled CT.

Lewis acid–base complex formation.5 Iodine is violet in the solid and gas phases, and in nondonor solvents such as trichloromethane. In water, propanone (acetone), or ethanol, all of which are Lewis bases, iodine is brown. The colour changes because a solvent–solute complex is formed from the lone pair of donor molecule O atoms and a low-lying * orbital of the dihalogen. The interaction of Br₂ with the carbonyl group of propanone is shown in Fig. 4.10. The illustration also shows the transition responsible for the new absorption band observed when a complex is formed. The orbital from which the electron originates in the transition is predominantly the lone pair orbital of the base (the ketone). The orbital to which the transition occurs is predominantly the LUMO of the acid (the dihalogen). Thus, to a first approximation, the transition transfers an electron from the base to the acid and is therefore called a charge-transfer transition. The triiodide ion, I₃^–, is an example of a complex between a halogen acid (I₂) and a halide base (I^–). One of the applications of its formation is to render molecular iodine soluble in water so that it can be used as a titration reagent:

The triiodide ion is one example of a large class of polyhalide ions (Section 17.8).

اخر الاخبار

اخبار العتبة العباسية المقدسة

تزامنًا مع حلول شهر ربيع الأول.. العتبة العباسية المقدسة ترفع مظاهر الحزن والسواد في المرقد الطاهر

بعد انتهاء شهري المحرم وصفر.. قسم الصيانة يباشر إدامة الثريات واستبدال مصابيح المرقد الطاهر

قسم الشؤون الخدمية يشرع بإدامة آليّات النظافة عقب انتهاء زيارة الأربعين

موكب عزاء الشعراء والرواديد ينظم مسيرة عزائية في ختام شهري الأحزان المحرم الحرام وصفر

المزيد

الآخبار الصحية

العنب.. فاكهة صغيرة بمفعول "خارق" للقلب والدماغ

دراسة تحدد "الحلقة المفقودة".. تسبب ارتفاع ضغط الدم

هذه الأطعمة تحمي دماغك من الشيخوخة وتزيد حدة الذكاء

خبراء يحذرون من مخاطر "الدهون المخفية" على القلب

المزيد

الآخبار التكنلوجية

الأرصاد الجوية تلجأ إلى الذكاء الاصطناعي.. لأي غرض؟

في منزلك.. "تعديل بسيط" يخفض ضغط الدم بشكل طبيعي

"ميزة جديدة" من إنستغرام تنافس تيك توك.. طال انتظارها

غوغل في مأزق.. بيانات 2.5 مليار مستخدم بقبضة القراصنة

المزيد

مواضيع ذات صلة

The classification of acids and bases

Group 14 Lewis acids

Group 13 Lewis acids

Lewis acids and bases of the s-block elements

Lewis acidity

Anhydrous sulfuric acid

Hydrogen fluoride

Liquid ammonia

Polyoxo compound formation

Amphoterism

Acidic and basic oxides

Periodic trends in aqua acid strength