Answer: c
Clarification: According to following mechanism we can say that some are major products. As we can see protonation of hydroxyl group followed by dehydration will leads to hydride shift to the adjacent positively charged carbon for formation of more stable carbocation. This will unleash two possibility of attack by Br- at the new carbocation from upward and backward and two products will be formed that are shown below.
6. Which of the following is not true for SN1 reactions?
a) They occur through a single step concerted reaction
b) They are favoured by polar solvents
c) Tertiary alkyl halides generally react through this mechanism
d) Concentration of nucleophile does not affect the rate of such reactions
Answer: a
Clarification: SN1 reaction is a two-step reaction, step one is the leaving group leaves, and the second step is the substrate forms a carbocation intermediate. Formation of carbocation intermediate is the rate determining step. Since for the formation of stable intermediate carbocation, highly polar solvent is required. The bulky substituents prevent the nucleophiles from approaching the carbon, which is attached directly to the halogen. SN1is also more favorable as the neighboring alkyl groups are electron donating, which helps to stabilize the carbocation. SN1 reaction because the nucleophile is not a part of the rate-determining step.
7. What is not true about below reaction?
.
a) Major product is given by SN1 reaction
b) Through E1 mechanism 3 alkenes are formed
c) 3-Methylpentane-3-ol is also formed as one of the product
d) Fractional distillation of elimination product will give two fractions
250+ TOP MCQs on Quantitative and Qualitative Analysis and Answers
Answer: d
Clarification: As we see below mechanism major product is formed by SN1 mechanism and E1 mechanism forms 3 alkenes. 3-Methylpentane-3-ol is also formed in the reaction. Fractional distillation of elimination product will give three fractions. Hence statement d is false.
8. What will be the total number of isomers formed when 2-methyl butane is subjected to monochlorination?
a) 5
b) 4
c) 3
d) 6
Answer: d
Clarification: Monochlorination of 2 methyl butane gives two pairs of enantiomers. 1st pair of enantiomer is 1-chloro-2-methyl butane and 2nd pair of enantiomer is 2-chloro-3-methyl butane.
1-chloro-3-methyl butane and 2-chloro-2-methyl butane products are also formed.
