Learning Objectives Compare the boiling points of amides with alcohols of similar molar mass. Compare the solubilities in water of amides of five or fewer carbon atoms with the solubilities of comparable alkanes and alcohols in water. With the exception of formamide (HCONH 2 ), which is a liquid, all simple amides are solids (Table \(\PageIndex{1}\)). The lower members of the series are soluble in water, with borderline solubility occurring in those that have five or six carbon atoms. Like the esters, solutions of amides in water usually are neutral—neither acidic nor basic. Condensed Structural Formula Name Melting Point (°C) Boiling Point (°C) Solubility in Water HCONH2 formamide 2 193 soluble CH3CONH2 acetamide 82 222 soluble CH3CH2CONH2 propionamide 81 213 soluble CH3CH2CH2CONH2 butyramide 115 216 soluble C6H5CONH2 benzamide 132 290 slightly soluble The amides generally have high boiling points and melting points. These characteristics and their solubility in water result from the polar nature of the amide group and hydrogen bonding (Figure \(\PageIndex{1}\)). (Similar hydrogen bonding plays a critical role in determining the structure and properties of proteins, deoxyribonucleic acid [DNA], ribonucleic acid [RNA], and other giant molecules so important to life processes. Physical Properties of Amides Solubility Water Solubility : Amides with five or fewer carbon atoms are generally soluble in water due to their ability to form hydrogen bonds with water molecules 1 2 . Solubility in Organic Solvents : Amides are also soluble in many organic solvents. Intermolecular Forces Hydrogen Bonding : Primary and secondary amides can form hydrogen bonds due to the presence of a hydrogen atom attached to the nitrogen. This significantly influences their physical properties 1 2 . Dipole-Dipole Interactions : Amides exhibit strong dipole-dipole interactions because of the polar nature of the amide group. Boiling Point High Boiling Points : Amides generally have higher boiling points compared to alcohols of similar molar mass. This is due to the strong hydrogen bonding and dipole-dipole interactions 1 2 . Comparison : For example, acetamide (ethanamide) has a boiling point of 222°C, which is higher than that of ethanol (78°C) despite having a similar molar mass 1 . Common Uses Solvents : Amides like N,N-dimethylformamide (DMF) are widely used as solvents in organic synthesis and industrial processes. Pharmaceuticals : Amides are found in various pharmaceuticals due to their stability and biological activity. Polymers : Polyamides, such as nylon, are used in the production of fibers and plastics. These properties make amides versatile and valuable in both industrial and pharmaceutical applications 1 2 3 . Classification of Amides Amides are classified based on the number of alkyl or aryl groups attached to the nitrogen atom: Primary Amides (1°) Structure : The nitrogen atom is bonded to one hydrogen atom and one carbonyl group. Example : Formamide (HCONH₂) General Formula : RCONH₂ Secondary Amides (2°) Structure : The nitrogen atom is bonded to one hydrogen atom, one carbonyl group, and one alkyl or aryl group. Example : N-Methylacetamide (CH₃CONHCH₃) General Formula : RCONHR’ Tertiary Amides (3°) Structure : The nitrogen atom is bonded to one carbonyl group and two alkyl or aryl groups. Example : N,N-Dimethylacetamide (CH₃CON(CH₃)₂) General Formula : RCONR’R’’ Intermolecular Forces and Physical Properties of Amides Primary Amides (RCONH 2 ) : Intermolecular Forces : Strong hydrogen bonding due to the presence of two hydrogen atoms attached to the nitrogen. Boiling and Melting Points : High, because of extensive hydrogen bonding. Solubility : Highly soluble in water due to the ability to form hydrogen bonds with water molecules 1 . Secondary Amides (RCONHR’) : Intermolecular Forces : Moderate hydrogen bonding as there is only one hydrogen atom attached to the nitrogen. Boiling and Melting Points : Lower than primary amides but still relatively high. Solubility : Soluble in water, but less so than primary amides 1 . Tertiary Amides (RCONR’R’') : Intermolecular Forces : No hydrogen bonding between amide molecules as there are no hydrogen atoms attached to the nitrogen. Boiling and Melting Points : Significantly lower than primary and secondary amides. Solubility : Less soluble in water because they can only accept hydrogen bonds from water molecules 1 2 . Key Takeaways Most amides are solids at room temperature; the boiling points of amides are much higher than those of alcohols of similar molar mass. Amides of five or fewer carbon atoms are soluble in water.