Like the H–O–H bond in water, the R–O–H bond is bent, and alcohol molecules are polar. This connection is especially evident in tiny molecules and reflected in the physical and lutz-heilmann.infoical properties of alcohols through low molar mass. Replacing a hydrogen atom from an alkane with an OH group permits the molecules to associate with hydrogen bonding (Figure (PageIndex1)).

You are watching: Why does ethanol have a high boiling point

Figure (PageIndex1): Intermolecular Hydrogen Bonding in Methanol. The OH teams of alcohol molecules make hydrogen bonding feasible.

Recall that physical properties are figured out to a huge extent by the type of intermolecular pressures. Table (PageIndex1) lists the molar masses and the boiling points of some prevalent compounds. The table shows that substances via comparable molar masses deserve to have rather various boiling points.

Table (PageIndex1): Comparison of Boiling Points and Molar Masses FormulaNameMolar MassBoiling Point (°C)
CH4 methane 16 –164
HOH water 18 100
C2H6 ethane 30 –89
CH3OH methanol 32 65
C3H8 propane 44 –42
CH3CH2OH ethanol 46 78
C4H10 butane 58 –1
CH3CH2CH2OH 1-propanol 60 97

Alkanes are nonpolar and are hence connected only via relatively weak dispersion forces. Alkanes through one to 4 carbon atoms are gases at room temperature. In contrast, also methanol (with one carbon atom) is a liquid at room temperature. Hydrogen bonding significantly boosts the boiling points of alcohols compared to hydrocarbons of equivalent molar mass. The boiling allude is a rough meacertain of the amount of energy necessary to sepaprice a liquid molecule from its nearemainder next-door neighbors. If the molecules communicate via hydrogen bonding, a fairly big quantity of power must be supplied to break those intermolecular attractions. Only then can the molecule escape from the liquid right into the gaseous state.

See more: Customer Reviews: Ouidad Curl Quencher Hydrafusion Intense Curl Cream

Alcohols can also engage in hydrogen bonding through water molecules (Figure (PageIndex2)). Thus, whereas the hydrocarbons are insoluble in water, alcohols with one to three carbon atoms are entirely soluble. As the length of the chain increases, yet, the solubility of alcohols in water decreases; the molecules come to be even more choose hydrocarbons and less prefer water. The alcohol 1-decanol (CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2OH) is basically insoluble in water. We commonly discover that the borderline of solubility in a family members of organic compounds occurs at 4 or five carbon atoms.