Name: alcohols and phenols: boiling point trends
Uploaded: 2023-04-30T18:28:39.000Z
Duration: 2 min 32 s
Channel: JoVE

In alcohols and phenols, the high electronegativity of oxygen relative to carbon and hydrogen leads to a partial negative charge on oxygen and partial positive charges on hydrogen and carbon.
The opposite partial charges of oxygen&#8211;hydrogen bond dipoles in adjacent alcohol or phenol molecules attract each other in hydrogen-bonding interactions. In an aqueous solution, alcohols and phenols form large networks of hydrogen bonds with water molecules, which enhances their water solubility.
The nonpolar regions of phenol or alcohol molecules are attracted by dispersion forces, like the interactions observed between hydrocarbons.
The additional energy required to disrupt the hydrogen bonding in addition to the dispersion forces causes an increase in the boiling points of alcohols and phenols compared to hydrocarbons of similar molecular weights.
The boiling points of alcohols increase with the size of the alkyl region due to the greater surface area for interactions through dispersion forces.
However, the increased surface area of the nonpolar region, where solvation by water is unfavorable, results in a lower solubility of alcohols in water.
An alcohol with branching in the chain is more

physical properties of alcohols and phenols

Physical Properties of Alcohols and Phenols

Alcohols are organic compounds in which a hydroxy group is attached to a saturated carbon. Phenols are a class of alcohols containing a hydroxy group attached to an aromatic ring. The physical properties of the alcohols and phenols are influenced by hydrogen bonding due to the oxygen&#8211;hydrogen dipole in the hydroxy functional group and dispersion forces between alkyl or aryl regions of alcohol and phenol molecules.
Alcohols possess a higher boiling point than aliphatic hydrocarbons of similar molecular weights due to intermolecular hydrogen bonding. As in hydrocarbons, the dispersion forces are the reason for the higher boiling point upon increasing carbon chain length.
Hydrogen bonding between the hydroxy group and water facilitates the solubility of alcohols in water. However, water solubility also depends on the length of the alkyl or nonpolar region of the molecule. Alcohols with an alkyl region of up to three carbon atoms are miscible with water. As the chain length increases, the increased surface area of the nonpolar region hinders solvation by the water molecules.
The solubility of branched alcohols is higher than that of linear alcohols of similar molecular weight. Branching reduces the surface area for intermolecular interactions between nonpolar regions; hence, the hydrophobic nonpolar region is smaller. Because of the weaker intermolecular interactions, the boiling points of branched alcohols are lower than the corresponding linear alcohols.
Multiple sites for hydrogen bonding in one molecule increase the boiling point; therefore, diols and amino alcohols possess higher boiling points and better water solubility than alcohols.
Compared to linear alcohols, cyclic alcohols can only exist in a limited number of conformations due to steric restrictions. The increased intermolecular interactions that arise from the close packing of cyclic alcohol in the liquid phase results in a higher boiling point as compared to that of a linear alcohol.
Intermolecular hydrogen bonds also play a role in defining phenols' high boiling point and solubility in water. The boiling point of phenol is higher than that of the corresponding aliphatic alcohol due to the close packing of phenol molecules, facilitated by &#960;&#8211;&#960; stacking interactions between the large, planar aromatic rings. Close-packed aromatic rings increase the surface area of the nonpolar region in the liquid phase and limit the solubility of phenol (9.3 g in 100 g H2O). However, this solubility is higher than that of alcohols with a similar molecular weight due to the increased polarity of the oxygen&#8211;hydrogen bond dipole induced by adjacent electron-withdrawing aromatic rings.
<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Structure</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Name</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Molecular weight (g/mol)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Boiling point (oC)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Solubility 
			
			(g/100 g H2O) 
			</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Butanol molecular structure, formula C4H9OH, chemical compound diagram, organic chemistry." src="/files/ftp_upload/11921/11921_PT_Figure_1.svg" style="text-align: center; height: 27px;" data-altupdatedat="1761830439000" data-alt="Figure1" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">1-Butanol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">74</td>
			<td style="color: black; border: 1px solid black; text-align: center;">118</td>
			<td style="color: black; border: 1px solid black; text-align: center;">9.1</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Organic compound, isopropanol, chemical structure diagram, molecular formula: C3H8O." src="/files/ftp_upload/11921/11921_PT_Figure_2.svg" style="text-align: center; height: 40px;" data-altupdatedat="1761830439000" data-alt="Figure2" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Isobutanol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">74</td>
			<td style="color: black; border: 1px solid black; text-align: center;">108</td>
			<td style="color: black; border: 1px solid black; text-align: center;">10</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Chemical structure, tert-butanol formula, 2-methylpropan-2-ol, organic chemistry diagram." src="/files/ftp_upload/11921/11921_PT_Figure_3.svg" style="text-align: center; height: 35px;" data-altupdatedat="1761830439000" data-alt="Figure3" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">tert-Butanol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">74</td>
			<td style="color: black; border: 1px solid black; text-align: center;">83</td>
			<td style="color: black; border: 1px solid black; text-align: center;">miscible (&#8734;)</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Chemical structure, carbon chain, molecular diagram, organic chemistry, molecular formula." src="/files/ftp_upload/11921/11921_PT_Figure_4.svg" style="text-align: center; height: 20px;" data-altupdatedat="1761830439000" data-alt="Figure4" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Pentane</td>
			<td style="color: black; border: 1px solid black; text-align: center;">72</td>
			<td style="color: black; border: 1px solid black; text-align: center;">36</td>
			<td style="color: black; border: 1px solid black; text-align: center;">insoluble</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Ethanol structural formula, chemical diagram, organic compound visualization, C2H6O molecular bonds." src="/files/ftp_upload/11921/11921_PT_Figure_5.svg" style="text-align: center; height: 55px;" data-altupdatedat="1761830439000" data-alt="Figure5" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Propane-1,2-diol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">76</td>
			<td style="color: black; border: 1px solid black; text-align: center;">188</td>
			<td style="color: black; border: 1px solid black; text-align: center;">miscible (&#8734;)</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Hexanol molecular structure diagram, showing carbon and hydroxyl group arrangement." src="/files/ftp_upload/11921/11921_PT_Figure_6.svg" style="text-align: center; height: 27px;" data-altupdatedat="1761830439000" data-alt="Figure6" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">1-Hexanol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">102</td>
			<td style="color: black; border: 1px solid black; text-align: center;">156</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0.6</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Cyclohexanol structure; chemical formula C6H12O; hydroxyl group attached; molecular diagram." src="/files/ftp_upload/11921/11921_PT_Figure_7.svg" style="text-align: center; height: 27px;" data-altupdatedat="1761830439000" data-alt="Figure7" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Cyclohexanol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">100</td>
			<td style="color: black; border: 1px solid black; text-align: center;">162</td>
			<td style="color: black; border: 1px solid black; text-align: center;">3.6</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Benzaldehyde molecular structure, chemical formula depiction, organic chemistry diagram." src="/files/ftp_upload/11921/11921_PT_Figure_8.svg" style="text-align: center; height: 70px;" data-altupdatedat="1761830439000" data-alt="Figure8" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Phenol</td>
			<td style="color: black; border: 1px solid black; text-align: center;">94</td>
			<td style="color: black; border: 1px solid black; text-align: center;">182</td>
			<td style="color: black; border: 1px solid black; text-align: center;">9.3</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Benzene ring structure with methyl group; chemical compound diagram; organic chemistry concept." src="/files/ftp_upload/11921/11921_PT_Figure_9.svg" style="text-align: center; height: 60px;" data-altupdatedat="1761830439000" data-alt="Figure9" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Toluene</td>
			<td style="color: black; border: 1px solid black; text-align: center;">92</td>
			<td style="color: black; border: 1px solid black; text-align: center;">110</td>
			<td style="color: black; border: 1px solid black; text-align: center;">insoluble</td>
		</tr>
	</tbody>
</table>
Alcohols are widely used as antiseptics due to their antibacterial properties. Isopropanol or ethanol is the major component of hand sanitizer. An ideal antibacterial agent should have a significant nonpolar region or alkyl region that can penetrate the cell membranes of microorganisms and destroy them. At the same time, it should have high solubility in the transport medium, which is water. In smaller alcohols, the optimal balance between these two conditions is fulfilled.

Alcohols are organic compounds in which a hydroxy group is attached to a saturated carbon. Phenols are a class of alcohols containing a hydroxy group ...

physical-properties-of-alcohols-and-phenols

Education

JoVE Core

Organic Chemistry

Unit 1

Alcohols and Phenols

KEY TERMS AND CONCEPTS

alcohols and phenols: boiling point trends

Alcohols and phenols are organic compounds whose physical properties depend on structure. In alcohols, a hydroxy group is attached to a saturated carbon. In phenols, the hydroxy group is attached to an aromatic ring.

Their boiling points and water solubility are shaped by hydrogen bonding and dispersion forces. The oxygen-hydrogen dipole in the hydroxy group allows intermolecular hydrogen bonding. This gives alcohols a higher boiling point than aliphatic hydrocarbons with similar molecular weights. As carbon chain length increases, dispersion forces also raise the boiling point.

Water solubility depends on both the hydroxy group and the nonpolar part of the molecule. Alcohols with up to three carbon atoms in the alkyl region are miscible with water. As the chain gets longer, the larger nonpolar surface makes solvation by water more difficult. Branched alcohols are usually more soluble than linear alcohols of similar molecular weight. They also have lower boiling points because branching weakens intermolecular interactions.

More hydrogen-bonding sites raise the boiling point and improve water solubility. That is why diols and amino alcohols show higher boiling points and better water solubility than simple alcohols. Cyclic alcohols can also have higher boiling points than linear alcohols because steric restrictions limit conformations and allow closer packing in the liquid phase.

Phenols also show strong intermolecular hydrogen bonding. Their boiling point is higher than that of the corresponding aliphatic alcohol because the large, planar aromatic rings pack closely and interact through pi-pi stacking. This close packing increases the nonpolar surface in the liquid phase and limits water solubility. Even so, phenol is more soluble in water than similar-mass alcohols because the aromatic ring increases the polarity of the oxygen-hydrogen bond dipole.

These trends help explain common examples such as 1-butanol, isobutanol, tert-butanol, propane-1,2-diol, 1-hexanol, cyclohexanol, phenol, pentane, and toluene. Alcohols are also widely used as antiseptics because of their antibacterial properties. Ethanol and isopropanol are major ingredients in hand sanitizer. Smaller alcohols work well because they balance a nonpolar region that can enter microbial membranes with enough water solubility to stay in the transport medium.

Alcohols and Phenols: Boiling Point Trends

alcohols-and-phenols-boiling-point-trends

structure and nomenclature of alcohols and phenols

structure-and-nomenclature-of-alcohols-and-phenols

Alcohols and Phenols: Naming Basics

Alcohols and phenols are important organic compounds with simple naming rules. Alcohols contain a hydroxyl group, or –OH group, directly bonded to carbon. Phenols also contain an OH group, but it is attached directly to a benzene ring. Alcohols are usually colorless. Phenol is a white crystalline compound with a characteristic hospital smell. These compounds are named using formal and standard systems. The most widely used system is the International Union of Pure and Applied Chemistry, or...

Alcohols and phenols are organic compounds whose physical properties depend on structure. In alcohols, a hydroxy group is attached to a saturated carbon. In phenols, the hydroxy group is attached to an aromatic ring. Their boiling points and water solubility are shaped by hydrogen bonding and dispersion forces. The oxygen-hydrogen dipole in the hydroxy group allows intermolecular hydrogen bonding. This gives alcohols a higher boiling point than aliphatic hydrocarbons with similar molecular...

acidity and basicity of alcohols and phenols

acidity-and-basicity-of-alcohols-and-phenols

Why Phenols Are More Acidic Than Alcohols

Alcohols are weak acids and weak bases because the O–H bond is polar and the oxygen atom has lone pairs. The partially positive hydrogen can be lost as a proton, and the oxygen can also accept a proton. When an alcohol is protonated, hydroxide changes into water, which is a much better leaving group. Alcohols vary a little in acidity. Methanol, with a pKa of 15.5, is slightly stronger as an acid than water, which has a pKa of 15.7. Ethanol, tert-butanol, and many other alcohols are weaker...

preparation of alcohols via addition reactions

preparation-of-alcohols-via-addition-reactions

Alcohol Synthesis from Alkenes

Alcohol synthesis from alkenes can follow three addition reactions: acid-catalyzed hydration, oxymercuration-demercuration, and hydroboration-oxidation. These methods all add across the double bond, but they give different alcohol products from the same alkene. In acid-catalyzed hydration, water adds to the double bond in an acidic atmosphere. The acid lets the hydrogen in water act as an electrophile and attack the alkene. A proton first adds to the double bond and forms a carbocation, which...

acid-catalyzed dehydration of alcohols to alkenes

acid-catalyzed-dehydration-of-alcohols-to-alkenes

Alcohol Dehydration Pathways to Alkene Products

Alcohol dehydration forms alkenes and water by removing a hydroxyl group and a hydrogen from a neighboring carbon. This reaction is usually done by heating the alcohol with an acid catalyst. Primary alcohols need higher temperatures and stronger acid conditions, while secondary and tertiary alcohols can react under milder conditions. Secondary and tertiary alcohols usually dehydrate through an E1 mechanism. In the first fast step, the alcohol is protonated and becomes an alkyloxonium ion. Then...

alcohols from carbonyl compounds: reduction

alcohols-from-carbonyl-compounds-reduction

Making Alcohols by Carbonyl Reduction

Making alcohols by carbonyl reduction is a key reaction in organic chemistry. It converts a carbonyl group into a hydroxyl group. The main routes are catalytic hydrogenation, hydride reduction, and borane reduction. Catalytic hydrogenation works by adding H2 across the pi bond of the carbonyl group. It uses transition metal catalysts such as Raney Ni, Pd-C, Pt, or Ru. Aldehydes and ketones can be reduced this way under mild to moderate heat, usually 25–100°C, and H2 pressure of about 1–5 atm.

alcohols from carbonyl compounds: grignard reaction

alcohols-from-carbonyl-compounds-grignard-reaction

Grignard Reagents in Alcohol Synthesis

Grignard reagents are key tools for making alcohols from carbonyl compounds. They are organomagnesium halides with a highly polar carbon–magnesium bond. Because this bond is partly ionic, the carbon acts as a strong nucleophile. It attacks the carbonyl carbon, which is the electrophilic part of a carbonyl group. Magnesium in the reagent also helps the reaction move forward. It coordinates with the carbonyl oxygen and lowers the electron density on the carbonyl carbon. This makes the carbonyl...

protection of alcohols

Alcohol Protecting Groups in Synthesis

Alcohol protecting groups help control which part of an organic molecule reacts during synthesis. A protecting group is a masking agent that makes a more reactive species inert under a chosen set of conditions. The lesson uses a pipe-flow analogy to show how this improves reaction selectivity. It also shows how protecting an alcohol can allow an organolithium alkylation of a halide to occur when the alcohol would otherwise compete. Common protecting groups for alcohols include trialkylsilyl...

preparation of diols and pinacol rearrangement

preparation-of-diols-and-pinacol-rearrangement

Pinacol Rearrangement of Vicinal Diols

Vicinal diols are compounds with two hydroxyl groups on adjacent carbon atoms. They are also called glycols. Under acidic conditions, these diols can undergo a pinacol rearrangement. The reaction starts when the acid catalyst transfers a proton to one hydroxyl group. This forms an oxonium ion. The oxonium ion then loses water and creates a tertiary carbocation intermediate. Next, a methyl group migrates from one carbon to the neighboring carbon. This step forms a resonance-stabilized cation...

conversion of alcohols to alkyl halides

Alcohols to Halides: Reagents and Mechanisms

Alcohols can be turned into alkyl halides by using reagents that make the hydroxyl group a better leaving group. The hydroxyl group is first protonated, which helps the reaction move forward. From there, the pathway can follow either an SN1 or SN2 substitution, depending on the starting alcohol and the reaction conditions. Tertiary alcohols usually form tertiary alkyl halides through a two-step SN1 mechanism. This route goes through a carbocation intermediate, and hyperconjugation helps...

oxidation of alcohols

Alcohol Oxidation Reagents and Products

Alcohol oxidation changes primary and secondary alcohols into carbonyl compounds. The reaction can mean loss of electrons, loss of hydrogen, or addition of oxygen. Oxidation is the opposite of reduction, so carbonyls can be reduced to alcohols, and alcohols can be oxidized back to carbonyls. The product depends on the alcohol type and the hydrogens on the alpha-carbon, the carbon next to the hydroxyl group. Primary alcohols can become aldehydes and then carboxylic acids. Secondary alcohols can...

preparation of alcohols via substitution reactions

preparation-of-alcohols-via-substitution-reactions

Alcohol Formation from Alkyl Halides

Alcohols can be made from alkyl halides by nucleophilic substitution. In these reactions, the carbon-halogen bond is highly polar, so the halide can leave the molecule. A nucleophile such as hydroxide ion or water then replaces the halide and forms an alcohol. The reaction path depends on the alkyl halide. Primary alkyl halides usually form primary alcohols through the SN2 mechanism. In SN2, the nucleophile attacks the halogen-bearing carbon from the side opposite the carbon-halogen bond. With...

key terms and concepts

Explore how hydrogen bonding, branching, chain length, and aromatic rings affect boiling point and water solubility in alcohols and phenols.

Alcohols and Phenols: Boiling Point Trends | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Alcohols and Phenols: Boiling Point Trends

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