Question

Would you predict the surface tension of \(t\) -butyl alcohol, \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH},\) to be greater than or less than that of \(\mathrm{n}\) -butyl alcohol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) Explain.

Short answer

Based on the analysis of intermolecular forces and molecular structures, the surface tension of n-butyl alcohol \(CH_{3}CH_{2}CH_{2}CH_{2}OH\) is expected to be greater than that of t-butyl alcohol \((CH_{3})_{3}COH\).

Step-by-step solution

Understanding t-butyl alcohol

t-butyl alcohol, \((CH_{3})_{3}COH\) has three methyl groups attached to a central carbon atom that is also attached to a hydroxyl group. The hydroxyl group (-OH) contributes to polarity, making it capable of forming hydrogen bonds.

Understanding n-butyl alcohol

n-butyl alcohol \(CH_{3}CH_{2}CH_{2}CH_{2}OH\) has a longer carbon chain. It also possesses a hydroxyl group at one end, making it capable of forming hydrogen bonds.

Comparing molecular structures

Comparing the two structures, n-butyl alcohol has a longer carbon chain compared to t-butyl alcohol. The longer carbon chain provides more opportunities for Van der Waals forces of attraction to occur, leading to stronger total intermolecular forces.

Relating molecular structure to surface tension

Surface tension is directly proportional to the magnitude of intermolecular forces. A substance with stronger intermolecular forces will have a higher surface tension. Given the analysis in the previous steps, n-butyl alcohol is expected to exhibit stronger intermolecular forces compared to t-butyl alcohol, due to its longer carbon chain and higher amount of Van der Waals forces.

Key concepts

t-butyl alcohol

t-butyl alcohol, also known scientifically as 2-methylpropan-2-ol, is an organic compound with the formula \(CH_{3})_{3}COH\. This molecule features a central carbon atom bonded to a hydroxyl group (-OH) and three methyl groups (\CH_3\). The structure of t-butyl alcohol gives it distinct characteristics. The presence of the hydroxyl group contributes to its polarity, enhancing its ability to form hydrogen bonds.
These hydrogen bonds are crucial as they determine many of the physical properties, including solubility and boiling point.
However, the three bulky methyl groups create a shape that is more spherical compared to straight-chain alcohols like n-butyl alcohol. This structural attribute influences how the molecules stack and interact with each other. This spherical form leads to lower surface tension, as the bulky shape can hinder effective intermolecular interactions beyond the hydrogen bonds. In summary, while t-butyl alcohol does have some ability to bond through hydrogen connections, its structural shape limits the potential strength and multiplicity of its intermolecular forces.

n-butyl alcohol

n-butyl alcohol, or butan-1-ol, has a linear chain structure given by the formula \(CH_{3}CH_{2}CH_{2}CH_{2}OH\). The hydrocarbon chain is straight, featuring four carbon atoms in a row.
At the end of this linear molecule is the hydroxyl group, like in t-butyl alcohol, which allows for hydrogen bonding.
However, a significant feature of n-butyl alcohol lies in its elongated chain. This chain enables additional interactions beyond hydrogen bonding, known as Van der Waals forces.

• More extensive contact surface area: The longer chain permits greater surface area interaction.
• Higher opportunity for Van der Waals forces: These forces arise due to temporary dipoles and are generally stronger with longer chains like that of n-butyl alcohol.

Because of these enhanced interactions, n-butyl alcohol typically exhibits stronger overall intermolecular forces than its more spherical counterpart, t-butyl alcohol. This increased force boosts the surface tension, lending to greater ability for the molecules to "stick" together at the surface.

intermolecular forces

Intermolecular forces are the invisible forces that influence how molecules interact with each other. They play a vital role in determining the physical properties of substances, particularly surface tension. Three main types of intermolecular forces include:

• Hydrogen bonding: Occurs when a hydrogen atom is attracted to an electronegative atom, such as oxygen. Both t-butyl and n-butyl alcohols engage in hydrogen bonding due to their -OH groups.


• Van der Waals forces: These are weaker forces that occur due to momentary changes in electron density. They include dispersion forces, which n-butyl alcohol experiences more due to its longer chain.


• Dipole-dipole interactions: Stronger than Van der Waals but usually weaker than hydrogen bonds, they occur between polar molecules, influenced by their shape and dipole moment.

Intermolecular forces collectively influence properties like boiling point and viscosity. In the case of surface tension, substances with stronger intermolecular forces tend to exhibit higher surface tension.
When comparing t-butyl and n-butyl alcohol, n-butyl's ability to form additional Van der Waals interactions due to its extended structure contributes to its higher surface tension compared to t-butyl alcohol.