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Zorluk: OrtaFunctional Groups, Homologous Series, and IUPAC Nomenclature

Arrange the following hydrocarbons in order of increasing boiling point, starting with the compound that has the lowest boiling point:

  1. 12,2-dimethylpropane
  2. 22-methylbutane
  3. 3pentane
  4. 4hexane

Cevap

The correct order from lowest to highest boiling point is 2,2-dimethylpropane, 2-methylbutane, pentane, and hexane.
Boiling points of alkanes depend on molecular mass and surface area contact. Hexane has the highest molecular mass and largest surface area, yielding the highest boiling point. Among the structural isomers of pentane, increased branching produces a more spherical shape with smaller surface contact area, reducing intermolecular van der Waals forces. Consequently, 2,2-dimethylpropane (most branched) has the lowest boiling point, followed by 2-methylbutane, straight-chain pentane, and finally hexane.

Adım Adım Çözüm

1
Compare molecular mass and carbon chain length among the given hydrocarbons.
hexane (C6H14C_6H_{14}) has a larger molecular mass and longer chain than the pentane isomers (C5H12C_5H_{12}), giving it the strongest London dispersion forces and highest boiling point.
Boiling point increases with molar mass in a homologous series due to increased electron cloud polarizability.
2
Compare the degree of branching among the structural isomers of pentane (C5H12C_5H_{12}).
2,2-dimethylpropane is highly branched (compact spherical shape), 2-methylbutane is moderately branched, and pentane is a straight chain.
Increased branching makes the molecule more spherical, reducing the surface area available for intermolecular van der Waals contact.
3
Rank all four compounds in order of increasing boiling point.
2,2-dimethylpropane < 2-methylbutane < pentane < hexane.
More branched isomers have lower boiling points than less branched isomers of the same molecular formula, and higher molar mass alkanes boil at higher temperatures than lower mass alkanes.

Anahtar Kavram

Effect of molecular mass and chain branching on alkane boiling points
Tahmini Süre:1m 0s
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Functional Groups, Homologous Series, and IUPAC Nomenclature

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