Olestra is a calorie-free fat substitute. The core of the...

Olestra is a calorie-free fat substitute. The core of the olestra molecule (Figure $\mathrm{P} 20.83$ ) is a disaccharide that has reacted with a carboxylic acid; this results in the conversion of hydroxyl groups on the disaccharide into the depicted structure. a. What is the name of the disaccharide core of the olestra molecule? b. What functional group has replaced the hydroxyl groups on the disaccharide? c. What is the formula of the carboxylic acid used to make olestra? (FIGURE CAN'T COPY)

Olestra is a calorie-free fat substitute. The core of the olestra molecule (Figure $\mathrm{P} 20.83$ ) is a disaccharide that has reacted with a carboxylic acid; this results in the conversion of hydroxyl groups on the disaccharide into the depicted structure.
a. What is the name of the disaccharide core of the olestra molecule?
b. What functional group has replaced the hydroxyl groups on the disaccharide?
c. What is the formula of the carboxylic acid used to make olestra?
(FIGURE CAN'T COPY)

Key Concepts

Disaccharide Core

A disaccharide is a carbohydrate composed of two monosaccharide units linked by glycosidic bonds. In this context, the core disaccharide used in olestra is sucrose—a molecule made up of a glucose and a fructose unit. Sucrose is widely used in synthetic modifications due to its multiple hydroxyl groups which can undergo esterification.

Esterification Reaction

Esterification is a chemical reaction in which an alcohol (–OH group) reacts with a carboxylic acid (–COOH group) to form an ester (–COOR) and water. In the formation of olestra, the hydroxyl groups on the sucrose molecule are converted into ester groups by reacting with carboxylic acids.

Carboxylic Acid Functional Groups

Carboxylic acids are organic compounds that contain the –COOH group. They serve as acyl donors in esterification reactions. In the context of olestra, a fatty acid (a long-chain carboxylic acid) reacts with the hydroxyl groups of sucrose to form ester linkages, resulting in a non-digestible sugar polyester.

Fatty Acids

Fatty acids are long-chain carboxylic acids that are key components of lipids. They feature a hydrophobic alkyl chain and a hydrophilic carboxyl group. In the synthesis of olestra, a specific fatty acid—commonly a C18 fatty acid like oleic acid, with the formula C18H34O2—is used to esterify the sucrose, contributing to the molecule’s fat-like properties while remaining non-caloric.

Transcript

00:01 We're given a molecule of olestra, as shown here, and we're asked three different questions about it.

00:07 This structure may look large and intimidating at first, but when we break it down to its essential components, it will become more clear to us.

00:14 Part a of this problem asks, what is the central disaccharide present in this molecule? when we hear disaccharide, we should be looking for this bond, which joins the two hydroxyl groups together, to link these two monomers.

00:30 These two structures should look very familiar to us as the one on the left is glucose, and the one on the right is fructose.

00:41 We can better visualize this when we look at glucose and fructose as they are normally as monomers.

00:48 We see that for each of them they have these oh groups, and both of those are still present in the molecule of olestra, except the h has been removed in a condensation reaction to be joined with all of these carboxylic acid groups.

01:07 But we can still see that the main framework of this central disaccharide is the monomers of glucose and fructose linked together.

01:20 And we know that glucose and fructose, the disaccharide that those two monomers form is sucrose.

01:29 And so that is the central disaccharide in alestra, and therefore the answer to part a.

01:38 For part b, we want to know these oh groups, what functional group have they been replaced with after that condensation reaction with the carboxylic acids? well, these are the functional groups that have been formed as a result of those condensation reactions.

01:59 And all we have to do is identify what that functional group is.

02:02 If we recall from our general list of different functional groups, that corresponds to esters.

02:16 And in case you forgot, an ester is just this general structure where r is a general side chain...

Please give Ace some feedback