Why does alcohol have a higher boiling and melting point than other hydrocarbons like alkanes? Is it because of a weak intermolecular force, or the alkyne has low pKa.
hydrogen bonding.
would that be why chloromethanol has a lower pKa than methanol?
No, the chlorine atom is quite electronegative, it pulls electrons so the H is not as tightly bound, therefore it is easier to be "ionized." Easier to ionize means stronger acidity and that is a smaller pKa.
so the conjugate base of chloromethanol is more stable than that of methanol
Yes but remember we may not be talking about much. If the pKa is 7, we are taking a Ka of 10^-7 and that changing to 10^-6 is large in terms are the number (10 times stronger) but 10^-6 still is a very weak acid.
I don't know what the pKa is for these two materials. The previous post was just an example.
The higher boiling and melting points of alcohols compared to alkanes can be attributed to the presence of polar hydroxyl (OH) groups in alcohols, which leads to stronger intermolecular forces.
To understand this, we need to consider the intermolecular forces present in both alcohols and alkanes. Alkanes, being hydrocarbons, consist only of carbon and hydrogen atoms and are therefore nonpolar molecules. The primary intermolecular force present in alkanes is London dispersion forces, which result from temporary fluctuations in electron distribution that create instantaneous dipoles.
On the other hand, alcohols contain the hydroxyl (OH) group, which introduces polarity into the molecule. The oxygen atom in the hydroxyl group is highly electronegative, attracting electrons towards itself and creating a partial negative charge. The hydrogen atom in the same group takes on a partial positive charge. This polarity allows alcohols to engage in additional intermolecular forces known as hydrogen bonding.
Hydrogen bonding is a strong intermolecular force that occurs when a hydrogen atom bonded to an electronegative atom (in this case, oxygen) interacts with another electronegative atom (such as oxygen or nitrogen) in a neighboring molecule. These hydrogen bonds are stronger than London dispersion forces and contribute significantly to the overall intermolecular attraction in alcohols.
The presence of hydrogen bonding in alcohols leads to higher boiling and melting points compared to nonpolar hydrocarbons like alkanes. When a liquid is heated, it requires energy to break the intermolecular forces and transition into a gaseous state (boiling). Similarly, when a solid is heated, energy is needed to overcome the intermolecular forces and convert it into a liquid state (melting). The stronger hydrogen bonding in alcohols requires more energy to break compared to the weaker London dispersion forces in alkanes, resulting in higher boiling and melting points for alcohols.
In summary, the higher boiling and melting points of alcohols compared to alkanes can be attributed to the presence of polar hydroxyl groups, which enable stronger intermolecular forces, specifically hydrogen bonding.