JEE (Based on NTA Guidelines-IIT Engg.) Mains Chemistry Coaching Programs
πΉ Video Course 2024 (0 Lectures [0 Mins]): Offline Support
Click Here to View & Get Complete Material
Rs. 100.00
1 Month Validity (Multiple Devices)
β³ π― Online Tests (1 Tests [30 Questions Each]): NTA Pattern, Analytics & Explanations
Click Here to View & Get Complete Material
Rs. 100.00
3 Year Validity (Multiple Devices)
π Study Material (159 Notes): 2024-2025 Syllabus
Click Here to View & Get Complete Material
Rs. 350.00
3 Year Validity (Multiple Devices)
π― 144 Numeric, 2994 MCQs (& PYQs) with Full Explanations (2024-2025 Exam)
Click Here to View & Get Complete Material
Rs. 650.00
3 Year Validity (Multiple Devices)
Chemistry Class 11 NCERT Solutions: Chapter 13 Hydrocarbons Part 10
Q: 17. Write down the products of ozonolysis of 1,2-dimethylbenzene (o-xylene) . How does the result support KekulΓ© structure for benzene?
Answer
o-xylene has two resonance structures:
All three products, i.e.. , methyl glyoxal, 1,2-demethylglyoxal, and glyoxal are obtained from two Kekule structures. Since all three products cannot be obtained from any one of the two structures, this proves that a-xylene is a resonance hybrid of two Kekule structures (I and II) .
Q: 18. Arrange benzene, n-hexane, and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.
Answer:
Acidic character of a species is defined on the basis of ease with which it can lose its H β atoms.
The hybridization state of carbon in the given compound is:
As the s β character increases, the electronegativity of carbon increases, and the electrons of bond pair lie closer to the carbon atom. As a result, partial positive charge of H β atom increases and ions are set free.
The s β character increases in the order:
Hence, the decreasing order of acidic behaviour is .
Q: 19. Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?
Answer
Benzene is a planar molecule having delocalized electrons above and below the plane of ring. Hence, it is electron-rich. As a result, it is highly attractive to electron deficient species i.e.. , electrophiles.
Therefore, it undergoes electrophilic substitution reactions very easily. Nucleophiles are electron-rich. Hence, they are repelled by benzene. Hence, benzene undergoes nucleophilic substitutions with difficulty.
Q: 20. How would you convert the following compounds into benzene?
(I) Ethyne
(II) Ethene
(III) Hexane
Answer
(I) Benzene from Ethyne:
(II) Benzene from Ethene:
(III) Hexane to Benzene: