Question 3 of 34beginner🔧 ApplyShort Answer3 marks

Draw formulas for the first five members of each homologous series beginning with the following compounds. (a) H–COOH (b) CH₃COCH₃ (c) H–CH=CH₂

(a)
Answer
  1. HCOOH
  2. CH₃COOH
  3. CH₃CH₂COOH
  4. CH₃CH₂CH₂COOH
  5. CH₃CH₂CH₂CH₂COOH
(b)
Answer
  1. CH₃COCH₃
  2. CH₃COCH₂CH₃
  3. CH₃COCH₂CH₂CH₃
  4. CH₃COCH₂CH₂CH₂CH₃
  5. CH₃COCH₂CH₂CH₂CH₂CH₃
(c)
Answer
  1. CH₂=CH₂
  2. CH₃CH=CH₂
  3. CH₃CH₂CH=CH₂
  4. CH₃CH₂CH₂CH=CH₂
  5. CH₃CH₂CH₂CH₂CH=CH₂

Explanation

A homologous series is a series of compounds with the same functional group and similar chemical properties, where each successive member differs by a −CH2−-CH_2- unit. For part (a), the series begins with methanoic acid (HCOOH) and adds a −CH2−-CH_2- group to get the next carboxylic acids. For part (b), the series begins with propanone (CH₃COCH₃) and adds −CH2−-CH_2- units to the alkyl chain to get higher ketones. For part (c), the series begins with ethene (CH₂=CH₂) and adds −CH2−-CH_2- units to get higher alkenes.

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