Hydrogen bonding Original Scenario-Based Practice

Questions

1. 1.

   During an expedition inside a cryo-cavern on an icy exomoon, planetary scientists isolate four volatile compounds of comparable molecular mass (32–34 g/mol) to evaluate them as potential biochemical markers: methanol ($\text{CH}_3\text{OH}$), fluoromethane ($\text{CH}_3\text{F}$), phosphine ($\text{PH}_3$), and silane ($\text{SiH}_4$). Thermal analysis reveals that only one of these substances displays an anomalously high boiling point due to extensive intermolecular hydrogen bonding. Which of these compounds forms intermolecular hydrogen bonds among its own molecules in the pure liquid state?

   • A) Methanol ($\text{CH}_3\text{OH}$), because its hydrogen atom is covalently bonded directly to a highly electronegative oxygen atom bearing lone pairs.
   • B) Fluoromethane ($\text{CH}_3\text{F}$), because it contains both fluorine, the most electronegative element, and peripheral hydrogen atoms.
   • C) Phosphine ($\text{PH}_3$), because phosphorus shares a valence group with nitrogen and possesses a lone pair bonded to three hydrogen atoms.
   • D) Silane ($\text{SiH}_4$), because the large number of hydrogen atoms surrounding the central atom creates four localized hydrogen-bonding sites.

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