The C-O-H bond angle of alcohol is:

less than tetrahedral angle

The correct answer is Option (1) → less than tetrahedral angle

The \(C-O-H\) bond angle in alcohols is a crucial aspect of their molecular geometry. Let us delve into the details of how this angle is determined and the factors that influence it.

Hybridization and Geometry of Alcohols

Hybridization: In alcohols, the carbon atom bonded to the hydroxyl group (-OH) is typically \(sp^3\) hybridized. This means that the carbon atom forms four sigma bonds (one with oxygen and three with hydrogen or other carbons).

Tetrahedral Arrangement: The four regions of electron density around an \(sp^3\) hybridized carbon atom adopt a

tetrahedral geometry. The ideal bond angles in a perfect tetrahedron are approximately 109.5°.

Influence of the Hydroxyl Group

The hydroxyl group \((-OH)\) introduces a new element to the bonding scenario:

Bonding: The carbon-oxygen (C-O) bond is formed by overlap of \(sp^3\) hybridized orbitals from carbon and p-orbitals from oxygen.

Lone Pairs: The oxygen atom in the hydroxyl group also has two lone pairs of electrons. These lone pairs can influence the overall geometry.

Lone Pair Repulsion

Repulsion Effects: Lone pairs occupy more space than bonding pairs because they are localized in a region of space. This leads to increased repulsion:

Lone pairs repel more strongly than bonding pairs, causing distortion in bond angles.

In alcohols, the presence of the lone pairs on the oxygen atom can push the \(C-O-H\) bond angle slightly downward, making it less than the ideal tetrahedral angle of 109.5°.

Actual Bond Angles in Alcohols

Experimental measurements show that the \(C-O-H\) bond angle in alcohols typically falls in the range of approximately 104° to 108°, depending on the specific alcohol. This value is indeed less than the ideal tetrahedral angle due to the effects mentioned above.

Summary

In summary, the \(C-O-H\) bond angle in alcohols is influenced by:

Hybridization of Carbon: The \(sp^3\) hybridization leads to an expected tetrahedral arrangement.

Presence of Lone Pairs: The two lone pairs on oxygen repel the bonding pairs, causing the angle to decrease.

Thus, the bond angle is: Less than the tetrahedral angle (109.5°).

Conclusion

Therefore, the \(C-O-H\) bond angle in alcohols is characterized as being less than the tetrahedral angle due to the presence of lone pairs on the oxygen atom that distort the ideal geometry.