Question

13. In the molecular orbital model of benzene, how many pi electrons are delocalized about the ring? A) 2 в) з C) 4 D) 5 E) 6 14, In the molecularorinl model of benzene,ow manypi electrons are in bonding molecular orbitals? A) 6 B) 5 C) 4 D) 3 E) 2 15. Cyelopentadiene is unusually acidic for a hydrocarbon. An explanation for this is the following statement A) The carbon atoms of cyclopentadiene are all sp'-hybridized B) Cyclopentadiene is aromatic. C) Removal of a proton from cyclopentadiene yields an aromatic anion. D) Removal of a hydrogen atom from cyclopentadiene yields a highly stable free radical Removal of a hydride ion from cyclopentadiene produces an aromatic cation. E) 16. Which of the following statements about cyclooctatetraene is NOT true? A) The compound rapidly decolorizes Br2/CCl4 solutions B) The compound rapidly decolorizes aqueous solutions of KMn04 C) The compound readily adds hydrogen. D) The compound is nonplanar E) The compound is comparable to benzene in stability 17. In the molecular orbital model of benzene, the six p orbitals combine to form how many molecular orbitals? A) 6 B) 5 C) 4 D) 3 E) 2

Answer 1

13) In benzene, there are 6 pi electrons which are delocalized. Delocalized electrons means the elecrons that are not associated with a single atom or covalent bond. Benzene has three double bonds and six carbon atoms with molecular formula C₆H₆ in which all the six carbns are sp² hybridised which shows that three double bonds are delocalized and thus its six electrons are also delocalized.

So the correct answer is E) 6

14) From the figure, it can be concluded that in bonding there are all three 6 pi electrons.

In benzene, there are 6 pi electrons which are delocalized. Delocalized electrons means the electrons that are not associated with a single atom or covalent bond. Benzene has three double bonds and six carbon atoms with molecular formula C_6H_6 in which all the six carbons are sp^2 hybridized which shows that three double bonds are delocalized and thus its six electrons are also delocalized. So the correct answer is E) 6 From the figure, it can be concluded that in bonding there are all three 6 pi electrons. Molecular orbitals of Benzene. So the correct answer is A) 6 Cyclo pentadiene looses a proton to form cyclopentadienyl anion which is aromatic as all the carbons are sp^2 hybridised, it is planar and have conjugated pi electron system and also follows 4n + 2 pi electrons huckel rule of aromaticity. Thus aromatic character makes cyclopentadienyl anion more stable. so we can say that cyclopentadiene behave as an acid and it looses a proton.

So the correct answer is A) 6

15) Cyclopentadiene looses a proton to form cyclopentadienyl anion which is aromatic as all the carbons are sp² hybridised, it is planar and have conjugated pi electron system and also follows 4n+2 pi electrons huckel rule of aromaticity. Thus aromatic character makes cyclopentadienyl anion more stable. so we can say that cyclopentadiene behave as an acid and it looses a proton.

So the correct option is C).

16) Cyclooctatetraene has conjugated 8 pi electrons but it is not aromatic as it is not planar and also it does not follow 4n+2 pi electrons huckel rule of aromaticity. Thus it is easily decolourised by bromine water and KMnO₄. The unplanar structure of cyclooctatetraene makes it unstable and thus it gets twisted to attain stability, so we cannot compare its stability with benzene which is highly stable due to its aromaticity.

So the correct option is E)