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Organic Chemistry – Some Basic Principles and Techniques · Question 70

AIPMT 2000MCQEasy📈 Topic in 0% papers+4−1
1

Which is maximum stable?

  1. 1-Butene
  2. cis-2-Butene
  3. trans-2-Butene
  4. All have same stability.

Answer

(3) trans-2-Butene

Solution

∵ Stability of an alkene increases with the number of alkyl groups on the doubly bonded carbons (more α-hydrogens ⇒ more hyperconjugation).

1-Butene (CH2=CH-CH2-CH3) is monosubstituted, while both 2-butenes (CH3-CH=CH-CH3) are disubstituted with 6 α-hydrogens.

⇒ 2-Butenes are more stable than 1-butene.

In cis-2-butene the two -CH3 groups are on the same side and repel each other (steric strain); in trans-2-butene they are on opposite sides.

∴ Stability order: trans-2-butene > cis-2-butene > 1-butene (also shown by their heats of hydrogenation: trans is the lowest).

Answer: (3)

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2

Polarisation in acrolein can be described as

  1. + CH2=CH- + CHO
  2. - CH2=CH- + CHO
  3. - CH2=CH-CH + O
  4. + CH2=CH-CH - O
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