Names of Aldehydes

Aldehydes and ketones with low molecular weights are often referred to by their common names. We will discuss the origin of these names—they are derived from the common names of acids—in Chapter 19. 

The lUPAC rules for naming aldehydes are similar to those outlined for alcohols. 

Name the longest continuous carbon chain that contains the carbonyl carbon atom as the parent chain. Replace the final -e of the parent hydrocarbon by the ending -al. 

Number the parent chain to make the carbonyl carbon atom C-1. The number 1 is not required because the position of the carbonyl carbon atom must be at the end of the chain. Determine the name of each substituent and the number of the carbon atom to which it is attached. Add this information to the parent name as a prefix. 

The aldehyde functional group has a higher priority than alkyl, halogen, hydroxyl, and alkoxy groups. If any of these groups is present, indicate their names and positions as prefixes to the name of the parent aldehyde. 

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Section 17 1 The substitutive lUPAC names of aldehydes and ketones are developed by identifying the longest continuous chain that contains the carbonyl group and replacing the final e of the corresponding alkane by al for aldehydes and one for ketones The chain is numbered m the direction that gives the lowest locant to the carbon of the carbonyl group... 

Like the other organic compounds you have encountered, the names of aldehydes and ketones are based on the names of the parent alkanes. 

Aldehydes contain a carbonyl group (C=0) to which at least one hydrogen atom is attached. The suffix -al is placed on the end of the name of aldehydes. For example, the molecule CH3CH2COH is known as propanal. Aldehydes must have the carbonyl on the last carbon on the chain (in order to have the hydrogen atom attached to the carbon). As a result, there is no need for the use of numbers to distinguish the position of the carbonyl group. 

Common names of aldehydes are derived from the common names of the corresponding carboxylic acids (Table 18-2). These names often reflect the Latin or Greek term for the original source of the acid or the aldehyde. Greek letters are used with common names of aldehydes to give the locations of substituents. The first... 

The common names of aldehydes are derived from the names of the corresponding carboxylic acids by replacing ic acid by -aldehyde. 

The lUPAC names of aldehydes follow the usual pattern. The longest chain carrying the —CHO group is considered the parent structure and is named by replacing the -e of the corresponding alkane by -al. The position of a substituent is indicated by a number, the carbonyl carbon always being considered as C l. Here, as with the carboxylic acids, we notice that C-2 of the lUPAC name corresponds to alpha of the common name. 

From the structures, write the common and I.U.P.A.C. names of aldehydes and ketones. 

Notice that the systematic names of aldehydes contain -al and that ketone names contain -one. 

In this chapter, we will study the naming of aldehydes and ketones, as well as some of their important reactions. These concepts will be very useful when we study the chemistry of carbohydrates in Chapter 7. 

The systematic names of aldehydes contain -al and that ketone names contain -one. Notice that testosterone has both alcohol and ketone groups the ketone functional group dominates the molecular properties. Therefore, testosterone is considered a ketone first and an alcohol second, and its name reflects its ketone properties. 

The lUPAC names of aldehydes are obtained by dropping the final -e and adding -al to the name of the parent hydrocarbon (i.e., the longest carbon-carbon chain carrying the —CHO group). The aldehyde carbon is always at the beginning of the carbon chain, is understood to be carbon number 1, and does not need to be numbered. The first member of the homologous series, H2C = 0, is methanal. The name methanol is derived from the hydrocarbon methane, which contains one carbon atom. The second member of the series is ethanal, the third member of the series is propanal, and so on ... 

Table 18.1 The names of aldehydes are derived from the name of the equivalent alkane, with the -e at the end ofthe name replaced by -al . Note that numbers are not needed when naming aldehydes, as the carbonyl group is always at the end ofthe carbon chain.

The names of aldehydes are derived from the name of the alkane with the -e at the end replaced by -al . 

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