For the following dehydrohalogenation (e2) reaction

For the following dehydrohalogenation (E2) reactio For the following dehydrohalogenation (E2) reaction, draw the major organic product(s), including stereochemistry.

Answer

General guidance

Concepts and reason
The problem is based on dehydrohalogenation of alkyl halides. The mechanism follows bimolecular elimination pathway. Here, the double bond is formed in the products in a single step. The strong base is used in these reactions.

Fundamentals

E2 mechanism is favoured by strong, negatively charged bases, especially and. The reaction occurs with primary, secondary and tertiary alkyl halides. So, the order of the reactivity would be tertiary > secondary > primary. Tertiary halide on dehydrohalogenation produces a more substituted alkene than a secondary or primary halide. Antielimination is favoured in case of bimolecular elimination reaction. In E2 mechanism, all the bonds are broken and formed in a single step.

Step-by-step

Step 1 of 2

The reaction is as follows: KOH
ethanol/heat
(E)-3-methylpent-2-ene
(2R,3R)-2-chloro-3-
methylpentane

The major organic product is as follows:


Treatment of (2R,3R)-2-chloro-3-methylpentane with a strong base, potassium hydroxide, in the presence of ethanol and heat gives (E)-3-methylpent-2-ene as a major organic product. Here, the base removes the proton from the carbon atom, so the leaving group (chloride) comes off and the double bond formation takes place. The elimination of leaving group and the abstraction of proton is in anti-fashion.

Step 2 of 2

The reaction is as follows: CH3CHOK
CH3CH OH
heat
(18,2R)-1-bromo-2-
methylcyclohexane

The major organic product is as follows: NO
or


Treatment of (1S,2R)-1-bromo-2-methylcyclohexane with a strong base, potassium ethoxide in the presence of ethanol and heat gives 1-methylcyclohex-1-ene as the major organic product. Here, the base removes the proton from the carbon atom, so the leaving group (bromide ion) comes off and the double bond formation takes place.

Answer

The major organic product is as follows:

The major organic product is as follows: NO
or

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