Difference WikiChemistry

Difference Between Acetal and Hemiacetal

Main Difference

The main difference between Acetal and Hemiacetal is that Acetal consists of primarily two –OR groups, whereas Hemiacetal consists of one -OH group and one -OR group.

Acetal vs. Hemiacetal

Acetal is considered as a group of atoms that is usually symbolized by a central carbon atom which is directly bonded to an –H group, two –OR groups, and –R group. On the other hand, hemiacetal is considered as a group of atoms that is made up of a central carbon atom directly bonded to four groups as an -R group, –OR group, -H group, -OH group. RHC(OR’)2 is given as the general formula of an acetal, while in its comparison, RHC(OH)OR’ is given as the general formula of the hemiacetal.

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Acetal can be produced from the reaction which occurs between an aldehyde group and alcohol; on the contrary of acetal, hemiacetal is produced as an intermediary of the reaction between an aldehydic group and alcohol, nucleophilic addition of an alcohol to resonance stabilized hemiacetal cation and half hydrolysis of an acetal. Acetal is known to be more stable when associated with a hemiacetal, while hemiacetal, on the other hand, is known to be less stable when compares with an acetal.

The examples of acetal are Benzylidene acetal, Dioxolane, Paraldehyde, Dimethoxymethane, Metaldehyde, Phenylsulfonylethylidene (PSE) acetal, Most glycosidic bonds in carbohydrates and many polysaccharides are acetal linkages, Cellulose, Polyoxymethylene, 1,1-Diethoxyethane; on its contrary, some examples of hemiacetal are Aldose, and Glucose.

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Comparison Chart

AcetalHemiacetal
Acetal is known as a functional group used explicitly for the aldehyde associated cases in which at least one hydrogen is present in place of an R on the central carbon atom.Hemiacetal is known as a compound that occurs when the alcohol adds an aldehyde or a ketone. It is a Greek word ‘Hemi’ which means half.
Considered As
Considered as a group of atoms that is typically symbolized by a central carbon atom which is directly bonded to an –H group, two –OR groups, and –R groupConsidered as a group of atoms which is made up of a central carbon atom directly bonded to four groups as an -R group, –OR group, -H group, -OH group
General Formula
RHC(OR’)2 is given as the general formulaRHC(OH)OR’ is given as the general formula
Formation
Can be produced from the reaction which occurs between an aldehyde group and an alcoholProduced as an intermediary of the reaction between an aldehydic group and alcohol, nucleophilic addition of an alcohol to resonance stabilized hemiacetal cation and half hydrolysis of an acetal
Stability
Known to be more stable when associated with a hemiacetalKnown to be less stable when compares with an acetal
Examples
The examples are Benzylidene acetal, Dioxolane, Paraldehyde, Dimethoxymethane, Metaldehyde, Phenylsulfonylethylidene (PSE) acetal, Most glycosidic bonds in carbohydrates and many polysaccharides are acetal linkages, Cellulose, Polyoxymethylene, 1,1-DiethoxyethaneAldose, and Glucose
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What is Acetal?

The group of atoms which are described as having the central carbon atom, which is then bonded to -R group, two –OR groups, and a –H group is known as acetal. The central carbon atom of acetal is mainly s­­p3 hybridized. The R groups of acetal are organic fragments and are alkyl groups, and all these R groups can be the same or different from each other.

RHC(OR’)2 is written as the standard formula of an acetal. An acetal is considered as geminal diether derived from a ketone and an aldehyde. Alkyl groups are frequently similar when bonded to oxygen atoms. The central carbon atom having two oxygen atoms is called acetal carbon. The group of acetal is known as a functional group.

Another type of acetal is Ketal. In ketal, the central carbon atom is attached with two –R groups and two –OR groups, and there are preset no hydrogen atom bonded to the central carbon atom. As the central carbon atom of acetal forms four bonds and hence, it is saturated, so it forms a tetrahedral geometry.

If the two alky groups of acetal are equivalent, which are attached with oxygen atoms, then it will be known as symmetrical acetal. But if the two alkyls are changed from each other, then they will be known as mixed acetal.

What is Hemiacetal?

A group of atoms that are mainly composed of a central carbon atom, which is then attached with four groups named as -OH group, a –H group, an –OR group, and -R group is known as hemiacetal. Hemiacetal is derived from Acetal, or if it is produced from a ketone, then it will be known as a hemiketal.

RHC(OH)OR’ is written as the general formula of hemiacetal in which the –OR group, which is attached with the central carbon atom, signifies an ether group, whereas the –OH group, which is also attached with the carbon atom, symbolizes the alcoholic group. That is why the hemiacetal is produced when the adding of alcohol into a carbonyl group occurs.

Alcohol contains –OH group that can attack the carbonyl group, and it is known as the nucleophilic addition reaction. In the production of acetals from aldehydes, the hemiacetal is produced as an intermediary between them. Hence, hemiacetals can either be produced by the process of partial hydrolysis of an acetal. Acetal can be formed when the reaction between an alcohol and a hemiacetal occurs.

Key Differences

  1. An Acetal is known as a functional group; on the other hand, hemiacetal is a compound that is derived from the ketones and aldehydes, respectively.
  2. The Acetal consists of a connectivity RHC(OR’)2 in which both R groups are considered organic fragments. The central carbon atom of Acetal consists of four bonds in it and hence is saturated and forms a tetrahedral geometry. At the same time, on its contrary, the general formula of hemiacetal is RHC(OH)OR’.
  3. The central carbon atom of acetal is directly bonded to an –H group, two –OR groups, and –R group; on its flip side, the central carbon atom of hemiacetal is directly bonded to four groups as an -R group, –OR group, -H group, -OH group.
  4. The formation of acetal is done from the reaction which happens between an aldehydic group and alcohol; on the other hand, the hemiacetal is formed by the formal addition of alcohol into a carbonyl group. Hemiacetal is formed as an intermediary of the reaction between an aldehydic group and alcohol, alcohol adding through nucleophilic addition reaction into resonance alleviated hemiacetal cation and a half break down of hydrogen of an acetal.
  5. The acetal is relatively considered more stable as compared to the hemiacetal; in its comparison, the hemiacetal is considered less stable as compared to the acetal.
  6. Benzylidene acetal, Dioxolane, Paraldehyde, Dimethoxymethane, Metaldehyde, Phenylsulfonylethylidene (PSE) acetal, Most glycosidic bonds in carbohydrates and many polysaccharides are acetal linkages, Cellulose, Polyoxymethylene, and 1,1-Diethoxyethane are some examples of acetal; on its contrary, an Aldose, and Glucose are the examples of the hemiacetal.

Conclusion

The above discussion concludes that both Acetal and Hemiacetal are functional groups. The difference between them is that Acetal contains two –OR groups. In its comparison, hemiacetal contains one –OH group and only one –OR group, and Hemiacetal is derived from Acetal and form as an intermediate in the reaction of Acetal.

Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss