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Difficulty: MediumFunctional Groups, Homologous Series, and IUPAC Nomenclature

Match each homologous series of organic compounds listed on the left with its correct general molecular formula on the right.

  • Alkanals (Aldehydes)CnH2nOC_n H_{2n}O
  • Alkanoic acids (Carboxylic acids)CnH2nO2C_n H_{2n}O_2
  • AlkynesCnH2n−2C_n H_{2n-2}
  • Alkanols (Alcohols)CnH2n+2OC_n H_{2n+2}O

Answer

Alkanals match with CnH2nOC_n H_{2n}O; Alkanoic acids match with CnH2nO2C_n H_{2n}O_2; Alkynes match with CnH2n−2C_n H_{2n-2}; Alkanols match with CnH2n+2OC_n H_{2n+2}O.
Each class of organic compound is defined by its characteristic functional group and degree of unsaturation. Alkanols are saturated single-oxygen compounds (CnH2n+2OC_n H_{2n+2}O), Alkanals feature one carbonyl double bond (CnH2nOC_n H_{2n}O), Alkanoic acids feature a carboxyl group (CnH2nO2C_n H_{2n}O_2), and Alkynes contain a triple bond reducing hydrogen content to CnH2n−2C_n H_{2n-2}.

Step-by-Step Solution

1
Determine the general formula for aliphatic monohydric alkanols.
Alkanols consist of an alkyl group (CnH2n+1C_n H_{2n+1}) bonded to a hydroxyl group (−OH-\text{OH}), giving the molecular formula CnH2n+2OC_n H_{2n+2}O.
Saturated aliphatic monohydric alcohols have the maximum possible hydrogen-to-carbon ratio for oxygenated single-bonded species.
2
Determine the general formula for alkanals.
Alkanals contain a terminal carbonyl group (−CHO-\text{CHO}), introducing one double bond (C=O\text{C=O}) which reduces the hydrogen atom count by two compared to alkanols, giving CnH2nOC_n H_{2n}O.
Each site of unsaturation (such as a π\pi-bond) decreases the hydrogen atom count by two.
3
Determine the general formula for alkanoic acids.
Alkanoic acids contain a carboxyl group (−COOH-\text{COOH}), giving two oxygen atoms and one carbon-oxygen double bond, yielding CnH2nO2C_n H_{2n}O_2.
Carboxylic acids are functional group isomers of esters and share the general formula CnH2nO2C_n H_{2n}O_2.
4
Determine the general formula for alkynes.
Alkynes possess one carbon-carbon triple bond (two π\pi-bonds), reducing the hydrogen count by four relative to alkanes (CnH2n+2C_n H_{2n+2}), resulting in CnH2n−2C_n H_{2n-2}.
A triple bond accounts for two degrees of unsaturation.

Key Concept

General Molecular Formulas of Organic Homologous Series
Estimated Time:1m 15s
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Topics

Functional Groups, Homologous Series, and IUPAC Nomenclature

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