Benzene
Transcript: Benzene Ring It has a six-carbon ring. Each of the carbons has sp2 hybridization. That gives it 120 degree bond angles all around the molecule. That makes it a perfect hexagon with a hydrogen atom sticking out from each point. Note that all these atoms are in the same plane. But that in itself is not what makes it special. Orbital diagram of benzene from top. If we turn the molecule on its side you can see that the sp2 hybridization leaves each carbon atom with one half-filled p orbital. Each of these forms pi bonds to neighbors on both sides, and the pi bonding goes all the way around the molecule. Orbital diagram of benzene from the side showing p-orbitals. For Kekule, benzene was a great challenge. He spent many years trying to work out the structure. Once, while thinking about the problem, he nodded off and had a day-dream. In it he saw a snake coil up, and suddenly grab its own tail. It then struck him that benzene might be a 'ring'. In a dream, Kekule saw a snake coil up, and grab its own tail. It struck him that benzene might be a 'ring'. Structures, pi bonds, singe bond, double bond, bond angle, hybrid structure, resonance energy, hexagonal ring, benzene. Biting one's own tail: the history of benzene What is benzene? Match the words with translation: Benzen Электронные облака orbitals Возбуждения электрона Aromatic compound Неспаренные электроны cyclic ring Двойная связь hexagonal form Температура плавления bond angle Температура кипения Double bond Гибридизированные орбитали Flammable liquid Угол связи Electron clouds Ненасыщенные соединения Valence bond Орбитали Unsaturated compounds Гексагональная форма Boiling temperature Исходное вещество для синтеза derivative Легковоспламеняющиеся жидкость Open chain Валентная связь Cyclic hydro carbon Производные Derivative Ароматический углеводород Excitation of electron Циклическое кольцо Hybridized orbitals Циклический гидракарбон Melting temperature Открытая цепь Umpaired electrons Исходное вещество для синтеза EXPERIENCE Teacher: Assilbekova H. N. Benzene Home work Work in pairs. Describe the structure of benzene. Exercises 3 1. A benzene molecule is a regular hexagonal structure with three ......... arranged in conjugated manner. 2. All the carbon-carbon bonds in benzene molecule are of equal bond length around 1.39 pm which is an intermediate value of carbon-carbon ............ (1.46 pm) and carbon -carbon ............... (1.34 pm) in hydrocarbons. 3. The molecule is a planer hexagonal geometry with the ........... of 120°. Sometime one structure of molecule cannot explain all the chemical properties of molecule, in such case more than one structure can be drawn for same molecule. 4. The difference between drawn structure and the resonance hybrid structure is known as ............. 5. For ............, there are two possible resonance structures given by Kekul and also called as Kekul structures. 6. Both resonating structure contains alternate double and single bonds and resonance hybrid shows with a ring in ............................... There are no individual localized pi bonds, just a big super pi bond. It is actually called a delocalized pi bond to distinguish it from the pi bonds that are localized alongside two carbon atoms to form the double and triple bonds that we dealt with earlier in this lesson. This super or delocalized pi bond is unusually stable. It will not react with bromine like the localized pi bond that is found in alkenes. Another way of saying this is that because the pi bond is not localized between, or associated with, just two carbon atoms, we have not really formed a double bond as such. Because of this, the electrons are not concentrated enough or available enough to react with the bromine. Orbital diagram of benzene showing pi bonding rings. [62orb14.JPG] This picture shows a close-up view of how the p orbitals overlap one another to form pi bonding all the way around the benzene molecule. The sigma bonds between adjacent carbon atoms are not shown in this picture. §7.8 Read the text Exercises 1 Exercises 2 Fill in the gaps with these words TERMS Kostanay State Pedagogical Institute Nature-mathematical faculty Benzene - organic compounds which are composed of carbon and hydrogen are called as hydrocarbons.The molecular formula of benzene is C6H6. Rubric 1. Benzene – Бензол 2. Open chain – открытая цепь 3. Сyclic hydrocarbon – циклическйий гидракарбон 4. cyclic ring – циклическое кольцо 5. aromatic compound – ароматический углеводород 6. double bond – двойная связь 7. derivative – производные 8. flammable liquid – легковоспламеняющиеся жидкость 9. precursor for a synthesis – исходное вещество для синтеза 10. hexagonal form – гексагональная форма 11. unsaturated compounds – ненасыщенные соединения 12. bond angle – угол связи 13. hybridized orbitals - гибридизированные орбитали 14. boiling temperature – температура кипения 15. melting temperature – температура плавления 16. valence bond – двойная связь 17. unpaired
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