7.7: Acyl Groups, RCO-

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1. The function R single bonded to a Carbon with a single bond and a double bonded oxygen. is called an acyl group and in specific cases in named by adding the suffix -oyl to the appropriate hydrocarbon prefix. That is, alkane- \(+\) -oyl becomes alkanoyl:

Left: H single bonded to a carbon with a double bonded O and a single bond. Labeled methanoyl (formyl). Middle: C H 3 single bonded to a carbon with a single bond and a double bonded O. Labeled ethanoyl (acetyl). Right: C H 3 C with a double bonded O, C H 2 C with a double bonded O and extra single bond. Labeled 3-oxobutanoyl.

Acyl groups also may be called alkanecarbonyl or cycloalkanecarbonyl groups:

Left: cyclohexane single bonded to a carbon with a double bonded O and an extra single bond. Labeled cyclohexanecarbonyl. Right: benzene ring single bonded to a carbon with a double bonded O and an extra single bond. Labeled benzenecarbonyl (benzoyl).

2. When an acyl group replaces the hydrogen of alcohols, carboxylic acids, hydrogen halides, ammonia or amines, we have the acyl compounds known as esters, anhydrides, halides, and amides, respectively.

R O shaded in grey single bond H adds an R C double bond O to get R C with a double bond O single bonded to the O R shaded in grey. Labeled esters.

Each of these types of compounds are named as follows.Image

Carboxylic Esters, \(RCO_2R'\)

1. The name of the parent carboxylic acid (alkanoic) is changed to alkanoate and is preceded, as in a separate word, by the name of the ester alkyl group \(R'\):

C H 3 C H 2 C H 2 C H 2 C double bonded to O and single bonded to O bonded to cyclohexane. Labeled cyclohexyl pentanoate.

2. When appropriate, esters also are named as carboxylates:

Cyclopropane single bonded to a carbon that is double bonded to O and single bonded to O C 2 H 5. Labeled ethyl cyclopropanecarboxylate.

3. When it is necessary to name the \(-CO_2R'\) function as a substituent, it becomes alkoxycarbonyl, . (Notice that this is structurally different from .)

Cyclohexane molecule with a C H 2 C H 2 C O 2 H substituent on carbon 1 and a C O 2 C H 3 substituent on carbon 3. Labeled 3-(3-methoxycarbonylcyclohexyl)propanoic acid.

Notice the use of parentheses to separate the numbering of \(C3\) of the cyclohexane ring from the numbering of the chain.

4. It also may be necessary at times to name the \(R'CO_2-\) group as a substituent, in which case it becomes acyloxy- or \(R'\)-carbonyloxy-. For example,

Carboxylic Anhydrides, \(RCOOCOR'\)

Symmetrical anhydrides (\(R=R'\)) are named after the parent acid; unsymmetrical or "mixed" anhydrides (\(R \neq R'\)) cite each of the parent acids:

Left: C H 3 C double bonded to O and single bonded to an O single bonded to C double bonded to O and single bonded to C H 3. Labeled ethanoic anhydride (acetic anhydride). Right: cyclohexane single bonded to a carbon double bonded to O and single bonded to an O single bonded to a carbon double bonded to O and single bonded to C H 2 C H 3. Labeled cyclohexanecarboxylic propanoic anhydride.

Acyl Halides, \(RCOX\)

The acyl group, \(RCO-\), and the halogen (as halide) are cited separately:

Left: C H 3 C double bonded to O and single bonded to C L. Labeled ethanoyl chloride (acetyl chloride). Middle: benzene single bonded to C that is double bonded to O and single bonded to B R. Labeled benzenecarbonyl bromide (benzoyl bromide). Right: cyclohexane single bonded to a C that is double bonded to O and single bonded to C L. Labeled cyclohexanecarbonyl chloride.

Amides, \(RCONH_2\)

1. The suffix amide is appended to the name of the hydrocarbon corresponding to the carbon chain that includes the carbonyl group. That is, alkan(e) \(+\) amide \(=\) alkanamide. A one-carbon chain is a carboxamide:

Left: C H 3 C double bonded to O and single bonded to N H 2. Labeled ethanamide (acetamide). Middle: C H 2 double bonded to C H C H 2 C double bonded to O and single bonded to N H 2. Labeled 3-butenamide. Right: cyclohexane single bonded to a C that is double bonded to O and single bonded to N H 2.

2. When the amide nitrogen is substituted with lower-ranking groups than the acyl group, the substituents are designated as prefixes. The letter N is used to show that the substitution is on nitrogen:

Benzene ring single bonded to a C double bonded to O and single bonded to an N that is single bonded to two C H 3 substituents. Labeled N, N-dimethylbenzenecarboxamide (N,N- dimethylbenzamide).

3. Names for amides as substituents include the following:

Contributors and Attributions

John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."