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Hydrocarbons

Nomenclature Guidelines

CBSE Class 11 Chemistry Chapter 13 Revision Notes

Let's learn about hydrocarbons: their types, naming, and characteristics!

Chapter 13: Hydrocarbons Revision Notes

  • Hydrocarbon: The term "hydrocarbon" refers to a carbon-hydrogen compound.
  • Saturated Hydrocarbon: If a hydrogen contains only C—C single bonds, it is said to be saturated. E.g. Ethane CH3—CH3
  • Unsaturated Hydrocarbon: If a hydrogen contains double (C=C) or triple bonds between the Carbon atoms they are said to be unsaturated hydrocarbons.

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  • Aromatic Hydrocarbon: Aromatic compounds include benzene and its derivatives.

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  • Alicyclic Compounds: Alicyclic or carbocyclic compounds are cyclic compounds that contain only carbon atoms.

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  • Heterocyclic Compounds: Heterocyclic compounds are cyclic compounds in which the ring atoms are carbon and another element (for example, N, S, or O).

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  • Alkanes: Alkanes are the most basic organic compounds, consisting solely of carbon and hydrogen.
  • CnHC2n+2 (where n = 1, 2, 3, etc.) is the general formula for them.
  • Single covalent bonds bind the carbon atoms in their molecules to one another. Alkanes are also known as saturated hydrocarbons because their carbon skeleton is fully saturated with hydrogens.
  • Alkanes have a lot of C—C and C—H bonds. As a result, this group of hydrocarbons is chemically inert. As a result, they're sometimes referred to as paraffins. Hydrocarbons make up the first three members of this class.

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  • Carbon forms single bonds with four hydrogen atoms in methane. The H—C—H bond angles are all 109.5 degrees. The structure of methane is tetrahedral. Head-on overlapping of sp3 hybrid orbitals of carbon and Is orbitals of hydrogen atoms forms C—C and C—H bonds.

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Nomenclature Guidelines

  • To write the IUPAC names from the structural formulas, use the step-by-step procedure below. Take a look at the following formula for a structural formula:

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Step 1: Determine which chain is the longest.

Step 2: Count the links in the chain: From left to right, the chain is numbered. The attached alkyl group receives the lowest numbers as a result of this.

Step 3: Determine the alkyl group.

  • Always keep in mind that

(a) commas are used to separate numbers.

(b) Hyphens are used to separate numbers from names;

(c) The prefixes di and tri are ignored when alphabetizing substituent names.

Relative Stability of Conformations

  • There are maximum repulsive forces, minimum energy, and maximum molecule stability in the staggered form of ethane.
  • When the staggered form becomes eclipsed, the electron clouds of the carbon hydrogen bonds become closer to each other, increasing electron cloud repulsions. As a result, the molecule requires more energy and thus has lower stability.
  • The magnitude of torsional strain is determined by the angle of rotation about the C—C bond. This angle is also known as torsional angle or dihedral angle.