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In an elimination reaction, two atoms or groups (YZ) are removed from the substrate with the formation of a pi bond.
depending on the reagents and conditions involved, elimination may be a first-order (E1) or second-order (E2).
Dehydration of Alcohol (E1)
Reactivity towards E2: R - I > R - Br > R - Cl > R - F
Question 1: Predict the elimination products of the following reactions.
(a) Sec. butyl bromide +
(b) 3-Bromo-3-ethylpentane + CH3OH
(c) 2-Bromo-3-ethylpentane + MeONa
(d) 1-Bromo-2-methylcyclohexane + EtONa
Sol. (a) CH3 - CH = CH -CH3
(b)
(c)
(d)
Question 2: major + minor
Write the structure of major and minor product.
Sol. (minor)
(major)
Promoting factors | E1 | E2 |
(i) Base | Weak base | Strong base required |
(ii) Solvent | Good ionizing solvent | Wide variety of solvent |
(iii) Substrate | 3° > 2° > 1° | 3° > 2° > 1° |
(iv) Leaving group | Better one required | Better one required |
Characteristics |
|
|
(i) Kinetics | K[R- X], I order | K[R - X] [Base], IIst order |
(ii) Orientation | Saytzeff alkene | Saytzeff alkene |
(iii) Stereochemistry | No special geometry is required | transition state must be co-planar |
Question 3: P + Q + R
Sol. P is , Q is
, R
Question 4: Arrange the compounds of each set in order of reactivity towards dehydrohalogenation by a strong base
(a) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane
(b) 1-Bromo-3-methylbutane, 2-bromo-2-methylbutane-2-Bromo-3-methylbutane
(c) 1-Bromobutane,1-Bromo-2,2-dimethylpropane, 1-bromo-2-methylbutane, 1-Bromo-3-methylbutane
In this reaction, a mixture of alkyl halide reacts with an aryl halide in the presence of dry ether and sodium. The resultant product is alkyl arene.
In this reaction, a mixture of haloarenes reacts with sodium in the presence of dry ether. The resultant product is diaryl.
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157 videos|385 docs|261 tests
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