Question

Chloral, \(\mathrm{Cl}_{3} \mathrm{C}-\mathrm{CH}=\mathrm{O},\) reacts with water to form the sedative and hypnotic agent chloral hydrate, \(\mathrm{Cl}_{3} \mathrm{C}-\mathrm{CH}(\mathrm{OH})_{2} .\) Draw Lewis structures for these substances, and describe the change in molecular shape, if any, that occurs around each of the carbon atoms during the reaction.

Short answer

The shape changes from trigonal planar to tetrahedral around the carbon atoms due to hydration.

Step-by-step solution

- Draw the Lewis Structure of Chloral

First, identify the valence electrons for each atom in the chemical formula \(\text{Cl}_3 \text{C}-\text{CH}=\text{O} \). Count the valence electrons: Carbon (C) has 4, each Chlorine (Cl) has 7, Hydrogen (H) has 1, and Oxygen (O) has 6. This will help in drawing the Lewis structure.

- Assemble the Lewis Structure of Chloral

Place the central carbon (C) atom and attach the three chlorine (Cl) atoms and one hydrogen (H) atom around it. Add a double bond between the second carbon (C) and the oxygen (O) atom. Distribute the remaining electrons to complete octets for each atom.

- Draw the Lewis Structure of Chloral Hydrate

In the chemical formula \(\text{Cl}_3 \text{C}-\text{CH}(\text{OH})_2 \), start similarly by counting valence electrons. Draw the central carbon (C) atom attached to three chlorines (Cl) and a central carbon (C) to which two hydroxyl (OH) groups are attached. Distribute the electrons to complete the octet rule.

- Describe Molecular Shapes of Chloral

Identify the shape around each carbon atom in chloral. Around the sp^2 hybridized carbon bonded to oxygen, the shape is trigonal planar.

- Describe Molecular Shapes of Chloral Hydrate

The shape around each carbon atom in chloral hydrate changes. The carbon bonded to the hydrogen and hydroxyl groups is sp^3 hybridized, resulting in a tetrahedral shape.

- Analyze Shape Changes

Compare the changes: Initially, the carbon with the double bond to oxygen had a trigonal planar shape. After hydration, the shape changes to tetrahedral, showing a significant shift in molecular geometry.

Key concepts

Valence Electrons

Valence electrons are the electrons in the outermost shell of an atom. These electrons are crucial to forming chemical bonds and determining the properties of molecules. In this exercise, you need to know the valence electrons of carbon (C), chlorine (Cl), hydrogen (H), and oxygen (O).
Each carbon atom has 4 valence electrons. Chlorine atoms each have 7 valence electrons. Hydrogen has just 1 valence electron. Oxygen, on the other hand, has 6 valence electrons. Counting these will help you draw the Lewis structures accurately.
For chloral \( \mathrm{Cl}_3 \mathrm{C}-\mathrm{CH}=\mathrm{O} \), we begin by summing the valence electrons for all atoms involved. This allows us to place the electrons systematically in the structure, ensuring every atom completes its octet (or duet, in the case of hydrogen).
Properly allocating the valence electrons is the first step in drawing correct Lewis structures and understanding the molecule's reactivity and properties.

Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms within a molecule. It influences the molecule's properties, reactivity, and interactions.
In chloral \( \mathrm{Cl}_3 \mathrm{C}-\mathrm{CH}=\mathrm{O} \), the carbon atom bonded to three chlorine atoms and one hydrogen atom forms a tetrahedral structure. The carbon adjacent to the double-bonded oxygen (C=O) is sp² hybridized, resulting in a trigonal planar shape around this carbon atom.
When chloral reacts with water to form chloral hydrate \(\mathrm{Cl}_3 \mathrm{C}-\mathrm{CH}(\mathrm{OH})_2 \), a change in molecular geometry occurs. The carbon originally involved in the double bond with oxygen loses this double bond, forming single bonds with two hydroxyl (OH) groups. This change from sp² to sp³ hybridization shifts the molecular geometry from trigonal planar to tetrahedral.
Understanding these shifts in molecular geometry is vital for predicting molecule behavior, reactivity, and interaction with other compounds.

Hybridization

Hybridization is a concept that describes the mixing of atomic orbitals to form new hybrid orbitals suitable for pairing electrons to form chemical bonds.
In chloral \( \mathrm{Cl}_3 \mathrm{C}-\mathrm{CH}=\mathrm{O} \), the carbon atom bonded to three chlorine atoms and one hydrogen atom is sp³ hybridized, forming tetrahedral molecular geometry. The carbon double-bonded to oxygen is sp² hybridized, leading to a trigonal planar shape. This indicates that the carbon atom mixes one s-orbital and two p-orbitals to accommodate three sigma bonds and one pi bond.
When chloral is converted to chloral hydrate \(\mathrm{Cl}_3 \mathrm{C}-\mathrm{CH}(\mathrm{OH})_2 \), that same carbon changes from sp² to sp³ hybridization. This creates a new hybrid orbital suited for forming single bonds with two hydroxyl groups, resulting in a tetrahedral shape around this carbon.
The change in hybridization from sp² to sp³ is significant as it impacts the molecule's shape and properties. Recognizing these hybridization changes can help you understand the stability, structure, and reactivity of the molecule.