Title Module 7 Aldehydes, Ketones and Carbohydrates.pdf ✅

CHEM 40: Basic Organic Chemistry Module 7: Aldehydes. Ketones, and Carbohydrates 1 This module is intended only for your personal use in connection with the course you are enrolled in. It is not for distribution or sale. Permission should be obtained from the Organic Chemistry and Natural Products Division for any use other than for what it is intended. This material has been reproduced and communicated to you by or on behalf of University of the Philippines pursuant to PART IV: The Law on Copyright of Republic Act (RA) 8293 or the “Intellectual Property Code of the Philippines.” The University does not authorize you to reproduce or communicate this material. This material may contain works that are subject to copyright protection under RA 8293. Any reproduction and/or communication of the material by you may be subject to copyright infringement and the copyright owners have the right to take legal action against such infringement. Do not remove this notice. MODULE 7. ALDEHYDES, KETONES, AND CARBOHYDRATES Aldehydes and ketones are groups of compounds containing the carbonyl group (C=O) and are important intermediates in many biological pathways, synthesis of pharmaceutical agents, and industrial processes. Low molecular weight aldehydes and ketones such as formaldehyde and acetone are important industrial solvents. The carbonyl compounds are also important in biochemistry and biology – many biomolecules present in plants and animals contain these functional groups. For instance, carbohydrates are aldehydes and ketones with multiple hydroxyl groups in their structures. In the first part of this module, you will learn about the general structure, nomenclature, physical properties, and preparations of aldehydes and ketones. The chemical reactions undergone by aldehydes and ketones will also be discussed. In the second part of this module, the application of carbonyl chemistry on carbohydrates is presented. You will also learn how to represent the structures of carbohydrates using Fischer projection, Haworth formula and chair conformation. Objectives At the end of this module, the students should be able to: ● write the structures and give the IUPAC names of aldehydes and ketones given their molecular formula ● describe the laboratory and industrial preparation of aldehydes and ketones ● predict the physical and chemical properties and chemical reactivity from their molecular structures ● identify the organic starting material, organic product, and/or necessary reagents for chemical reactions of aldehydes and ketones ● understand the outcome of reactions based on the mechanism
CHEM 40: Basic Organic Chemistry Module 7: Aldehydes. Ketones, and Carbohydrates 2 This module is intended only for your personal use in connection with the course you are enrolled in. It is not for distribution or sale. Permission should be obtained from the Organic Chemistry and Natural Products Division for any use other than for what it is intended. ● distinguish aldehydes and ketones using simple chemical tests ● draw the structure of carbohydrates using Fischer projection, Haworth formula and chair conformation ● classify carbohydrates as mono-, oligo- and polysaccharides ● classify monosaccharides based on the number of carbons and type of carbonyl group ● differentiate reducing from non-reducing sugars; and ● correlate properties of carbohydrates with their structures 7.1. ALDEHYDES AND KETONES 7.1.1. General Structure The carbonyl carbon of aldehydes and ketones is bonded to either hydrogen or another carbon atom. A ketone has alkyl or aryl groups attached to the carbonyl carbon whereas an aldehyde has one alkyl or aryl group and a hydrogen atom bonded to the carbonyl compound (Figure 7-1). Figure 7-1. General structures of aldehydes and ketones. The carbonyl carbon is sp2 -hybridized, the three atoms attached to it are in a trigonal planar arrangement and the expected bond angle is around 120o . The double bond between the carbonyl carbon and the carbonyl oxygen is composed of one sigma bond and one pi bond. The sigma bond is formed via the overlap of two sp2 -hybridized orbitals. The pi bond, on the other hand, is formed via the overlap of the carbon p orbital with the unhybridized p orbital of oxygen. 7.1.2. Nomenclature a. Aldehydes In naming aldehydes, the parent chain should include the –CHO group and is named by identifying the corresponding alkane and replacing the –e ending with –al. In numbering the parent chain, the carbonyl carbon is assigned as carbon 1. Consider the example below: Example 7-1
CHEM 40: Basic Organic Chemistry Module 7: Aldehydes. Ketones, and Carbohydrates 3 This module is intended only for your personal use in connection with the course you are enrolled in. It is not for distribution or sale. Permission should be obtained from the Organic Chemistry and Natural Products Division for any use other than for what it is intended. In Example 7-1, the structure drawn in red is the parent chain. The parent chain, numbered such that the carbonyl carbon is assigned as carbon 1, has six carbons and the corresponding alkane name is hexane. The –e ending is replaced with –al and becomes hexanal. A methyl substituent (drawn in black) is located at carbon 5 and the compound is therefore named as 5-methylhexanal. If a C=C or CΞC is present on the chain, the chain is named as an alkene (or alkyne) and the –e ending is replaced with –al. The carbonyl carbon is still assigned as carbon 1. The position number of the alkene (or alkyne) is placed before the name of the parent chain. Consider the following examples: Example 7-2 Example 7-3 In Examples 7-2 and 7-3, the parent chain has 5 carbons and is numbered such that the carbonyl carbon is assigned as carbon 1. The corresponding alkene name of Example 7-2 is 4- pentene, the –e ending is replaced with –al and becomes 4-pentenal. A methyl substituent (drawn in black) is located at carbon 3 and the compound is therefore named as 3-methyl-4-pentenal. On the other hand, the corresponding alkyne name of Example 7-3 is 4-pentyne, the –e ending is replaced with –al and becomes 4-pentynal. A methyl substituent (drawn in black) is located at carbon 3 and the compound is therefore named as 3-methyl-4-pentynal. Other functional groups such as ketone (oxo), –NH2 (amino), –OH (hydroxy), –OR (alkoxy), and –X (halo) have lower priorities than the aldehyde group and are simply treated as substituents. The following examples are variation of Example 7-1 in which the methyl group is replaced by these functional groups: