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प्रश्न
Given reasons: SN1 reactions are accompanied by racemization in optically active alkyl halides.
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उत्तर
In SN1 reaction, formation of carbocation as an intermediate takes place. This carbocation has sp2-hybridised and planar structure. This planar carbocation is attacked by nucleophile from both the sides equally to form d and l isomers in equal proportion. Such products are called racemic mixture. Hence, SN1 reactions are accompanied by racemisation in optically active alkyl halides.
संबंधित प्रश्न
What happens when ethyl chloride is treated with aqueous KOH?
Which one is most reactive towards SN1 reaction?
An important chemical method to resolve a racemic mixture makes use of the formation of ______.
Which of the following is a chiral compound?
In SN1 reactions, the correct order of reactivity for the following compounds:
CH3Cl, CH3CH2Cl, (CH3)2CHCl and (CH3)3CCl is ______.
Optical activity of an enantiomeric mixture is +12.6° and the specific rotation of (+) isomer is +30°. The optical purity is ______ %.
Complete the reaction with the main product formed:
Give the mechanism of the following reaction:
\[\ce{CH3CH2OH ->[H2SO4][413 K] CH3CH2-O-CH2CH3 + H2O}\]
The following questions are case-based questions. Read the passage carefully and answer the questions that follow:
|
Nucleophilic Substitution: Influences of solvent polarity: The reaction rate (SN2) of 2-bromopropane and NaOH in ethanol containing 40% water is twice slower than in absolute ethanol. Hence the level of solvent polarity has an influence on both SN1 and SN2 reactions but with different results. Generally speaking, a weak polar solvent is favourable for SN2 reaction, while a strong polar solvent is favourable for SN1. Generally speaking, the substitution reaction of tertiary haloalkane is based on SN1 mechanism in solvents with a strong polarity (for example ethanol containing water). |
Answer the following questions:
(a) Why racemisation occurs in SN1? (1)
(b) Why is ethanol less polar than water? (1)
(c) Which one of, the following in each pair is more reactive towards SN2 reaction? (2)
(i) CH3 – CH2 – I or CH3CH2 – Cl
(ii)
OR
(c) Arrange the following in the increasing order of their reactivity towards SN1 reactions: (2)
(i) 2-Bromo-2-methylbutane, 1-Bromo-pentane, 2-Bromo-pentane
(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 2-Bromo-3- methylbutane
The correct order of increasing reactivity of
C-X bond towards nucleophile in the following compounds is:
