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Chemistry Class - 11: Chapter β 13. Hydrocarbons Part β 4 Questions and Answers
III. Short Answer Type
Question: 20
Why do alkenes prefer to undergo electrophilic addition reaction while arenas prefer electrophilic substitution reactions? Explain
Answer:
Both alkenes and arenas are electron-rich. Therefore, undergo electrophilic reactions. Olefins undergo addition reactions because addition of a reagent to an olefin gives a more stable product as sp2 hybridization changes to sp3 hybridization. Addition to the double bond of an arena would give a product with less or no resonance stability hence addition is difficult arenas. On the other hand, in substitution reaction resonance stabilization is retained therefore, arenas undergo substitution reaction.
Question: 21
Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will the butane thus formed on reduction of 2-butyne show the geometrical isomerism?
Answer:
2-Butene can show geometrical isomerism.
Question: 22
The rotation about bond is restricted because of repulsion between electron cloud of bonds on either carbon atoms.
Answer:
The rotation about bond is restricted because of repulsion between electron cloud of bonds on either carbon atoms.
Question: 23
Draw Newman and Sawhorse projections for the eclipsed and staggered conformations of ethane. Which of these conformations is more stable and why?
Answer:
Question: 24
The intermediate carbocation formed in the reactions of HI, and with propene is the same and the bond energy of , and is , and respectively. What will be the order of reactivity of these halogen acids?
Answer:
Bond dissociation energy is least for and maximum for therefore, order of reactivity will be .
Question: 25
What will be the product obtained as a result of the following reaction and why?
Answer:
Propyl chloride forms less stable carbocation with anhydrous which rearranges to a more stable carbocation and gives isopropyl benzene as the product of the reaction.
Question: 26
How will you convert benzene into (i) (ii)
Answer:
Question: 27
Arrange the following set of compounds in the order of their decreasing relative reactivity with an electrophile. Give reason.
Answer:
The + R effect of and has a β R effect. Relative reactivity of the substituted benzene rings is as follows:
Question: 28
Despite their - I effect, halogens are o- and p-directing in haloarenes. Explain
Answer:
Halogens attached to benzene rings exert β I and + R effect. + R effect dominates β I effect and increases the electron density at ortho and para positions of the benzene ring with respect to halogens.
Question: 29
Why does presence of a nitro group make the benzene ring less reactive in comparison to the unsubstituted benzene ring. Explain.
Answer:
Question: 30
Suggest a route for the preparation of nitrobenzene starting from acetylene?
Answer:
Question: 31
Predict the major product (s) of the following reactions and explain their formation
Answer: