The C - O - C bond angle in dimethyl ether is:

• A. 111.7°
• B. 108.5°
• C. 109°
• D. 120°

To determine the C-O-C bond angle in dimethyl ether, we first need to understand the molecular structure of this compound. Dimethyl ether (DME) has the formula CH3-O-CH3, where two methyl groups (CH3) are bonded to an oxygen atom. The geometry around the oxygen atom is crucial for understanding the bond angles.

Understanding Molecular Geometry

In dimethyl ether, the oxygen atom is bonded to two carbon atoms and has two lone pairs of electrons. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the arrangement of electron pairs around a central atom determines the molecular geometry. For oxygen in dimethyl ether:

• There are two bonding pairs (C-O bonds).
• There are two lone pairs of electrons.

Determining the Bond Angle

With four regions of electron density (two bonding pairs and two lone pairs), the geometry around the oxygen atom is classified as tetrahedral. However, the presence of lone pairs affects the bond angles due to their repulsive nature. Lone pairs take up more space than bonding pairs, which compresses the bond angles between the atoms.

In a perfect tetrahedral arrangement, the bond angles would be 109.5 degrees. However, because of the two lone pairs on the oxygen, the C-O-C bond angle is slightly reduced. The typical bond angle for C-O-C in dimethyl ether is approximately 111.7 degrees. This is slightly larger than the ideal tetrahedral angle due to the influence of the lone pairs.

Final Answer

Therefore, the correct answer to the bond angle in dimethyl ether is A. 111.7°.

Visualizing the Structure

To visualize this, imagine the oxygen atom at the center with the two methyl groups extending outwards. The lone pairs are positioned above and below the plane formed by the carbon atoms, which pushes the carbon atoms slightly apart, resulting in the observed bond angle.

In summary, the C-O-C bond angle in dimethyl ether is influenced by the tetrahedral arrangement of electron pairs around the oxygen atom, leading to a bond angle of approximately 111.7 degrees. This understanding of molecular geometry is essential in predicting the behavior and reactivity of various compounds in organic chemistry.