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Zorluk: OrtaIntermolecular Forces and Hydrogen Bonding

Ethanol (C2H5OHC_2H_5OH) and dimethyl ether (CH3OCH3CH_3OCH_3) are structural isomers with the same relative molecular mass (46 g mol−146\text{ g mol}^{-1}). However, ethanol boils at 78.4∘C78.4^\circ\text{C} while dimethyl ether boils at −24∘C-24^\circ\text{C}. Which of the following statements correctly explains this difference in boiling points?

  1. Ethanol molecules are held together by strong intermolecular hydrogen bonding, whereas dimethyl ether molecules experience weaker dipole-dipole interactions.Cevap
  2. B
    The intramolecular O−HO-H covalent bond in ethanol requires more thermal energy to break than the C−OC-O covalent bond in dimethyl ether during boiling.
  3. C
    Dimethyl ether has weaker London dispersion forces because its effective molecular weight in the liquid state is lower than that of ethanol.
  4. D
    Ethanol undergoes complete ionic dissociation in liquid phase, resulting in strong electrovalent attractions between ions.

Cevap

Ethanol molecules are held together by strong intermolecular hydrogen bonding, whereas dimethyl ether molecules experience weaker dipole-dipole interactions.
The correct answer identifies that ethanol can form strong intermolecular hydrogen bonds due to its hydroxyl group (−OH-OH), while dimethyl ether lacks a hydrogen atom attached directly to an electronegative atom and relies only on weaker dipole-dipole and van der Waals forces. Consequently, ethanol requires significantly higher thermal energy to separate its molecules into the gas phase.

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1
Analyze the molecular structures of ethanol (C2H5OHC_2H_5OH) and dimethyl ether (CH3OCH3CH_3OCH_3).
Ethanol contains a hydrogen atom directly bonded to oxygen (−OH-OH), enabling hydrogen bond donation and acceptance. Dimethyl ether (CH3−O−CH3CH_3-O-CH_3) has oxygen bonded only to carbon atoms, preventing hydrogen bond formation between its own molecules.
Hydrogen bonding requires a hydrogen atom attached to a highly electronegative atom (NN, OO, or FF).
2
Compare the nature and strength of intermolecular forces in both compounds.
Ethanol exhibits strong intermolecular hydrogen bonding in addition to dipole-dipole and dispersion forces. Dimethyl ether exhibits only dipole-dipole forces and dispersion forces.
Hydrogen bonds are significantly stronger than permanent dipole-dipole attractions.
3
Relate intermolecular force strength to boiling point trends.
More thermal energy is needed to separate ethanol molecules during vaporization, giving ethanol a much higher boiling point (78.4∘C78.4^\circ\text{C}) compared to dimethyl ether (−24∘C-24^\circ\text{C}).
Boiling point increases with stronger intermolecular forces of attraction.

Anahtar Kavram

Intermolecular Hydrogen Bonding vs. Dipole-Dipole Attractions
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Konular

Intermolecular Forces and Hydrogen Bonding

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