Textbook Question
What are the systematic names of the following compounds? Indicate the configuration (R or S) of each asymmetric center.
a. D-glucose
21. Aldehydes and Ketones: Nucleophilic Addition
Naming Aldehydes
3:21 minutesProblem 2
Textbook Question
Why are numbers not used to designate the position of the functional group in propanone and butanedione?
Verified step by step guidance1
Understand the structure of the compounds: Propanone (commonly known as acetone) has the molecular formula CH₃COCH₃, and butanedione (commonly known as diacetyl) has the molecular formula CH₃COCOCH₃. Both are ketones, meaning they contain a carbonyl group (C=O) bonded to two carbon atoms.
Recall the IUPAC naming rules for ketones: The position of the carbonyl group is indicated by a number if it is necessary to distinguish its location. The numbering starts from the end of the carbon chain closest to the carbonyl group to give it the lowest possible number.
Analyze the structure of propanone: In propanone, the carbonyl group is always located on the second carbon atom because the molecule has only three carbon atoms. Since there is no ambiguity in the position of the carbonyl group, a number is not required in the name.
Analyze the structure of butanedione: In butanedione, there are two carbonyl groups, each located on the second and third carbon atoms of the four-carbon chain. The positions of these groups are fixed and symmetric, so there is no need to specify their locations with numbers in the name.
Conclude the reasoning: Numbers are not used to designate the position of the functional group in propanone and butanedione because the positions of the carbonyl groups are unambiguous and fixed by the structure of the molecules. Including numbers would be redundant in these cases.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In organic chemistry, the presence and position of functional groups significantly influence the properties and reactivity of compounds. Understanding functional groups is essential for naming and classifying organic compounds.
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IUPAC Nomenclature
The International Union of Pure and Applied Chemistry (IUPAC) nomenclature provides a systematic method for naming organic compounds. According to IUPAC rules, the position of functional groups is indicated by numbers only when necessary for clarity. In cases where the functional group is at a position that is universally understood, such as in propanone and butanedione, numbering is often omitted.
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Structural Isomerism
Structural isomerism occurs when compounds have the same molecular formula but different structural arrangements of atoms. In the case of propanone (a ketone) and butanedione (a diketone), the functional groups are positioned in such a way that their locations are inherently clear from the molecular structure. This clarity allows for the omission of numbers in their names, as the functional groups' positions are implied.
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