Problem 15 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is known as leavulose sugar? (a) glucose (b) fructose (c) surcose (d) arabinose

Step-by-Step Solution

Answer

Fructose is known as leavulose sugar.

Step 1: Understand the Terminology

The term encountered here is 'leavulose'. To understand the exercise, first recognize that 'leavulose' is another name for a specific type of sugar. It refers to the same substance we need to identify in the given options.

Step 2: Match Terminology with Options

Next, compare the term 'leavulose' with the options provided: (a) glucose, (b) fructose, (c) sucrose, (d) arabinose. Leavulose is an alternative name for fructose, frequently used because fructose is a ketohexose with a specific arrangement that makes it "left-rotating" optically, hence the name 'leavulose'.

Step 3: Verify and Confirm

Finally, support the connection between 'leavulose' and fructose. Fructose is well-known in scientific and culinary contexts as 'fruit sugar', sweet and found in various fruits and honey. By verifying these facts, we confirm that fructose is indeed the correct answer.

Key Concepts

Understanding Leavulose

Leavulose is an interesting term that might not be as widely recognized as some other sugar names. It's actually an older term used to describe fructose, one of the sugars you're likely familiar with from fruits and honey. Let's delve into why fructose is called leavulose.

The name "leavulose" comes from the way fructose interacts with polarized light. When a solution of fructose is placed between polarizing plates, it causes the light to rotate to the left, which in scientific terms is known as levorotation. This unique optical activity is why fructose earns the name "leavulose". Remember, this leftward rotation is a defining characteristic, setting it apart from other sugars like glucose, that don't share this property.

So next time you hear "leavulose", you'll know it's just another name for the sweet fructose, mainly because of its optical properties.

Defining Ketohexose

Ketohexose is a particular group of sugars, and fructose fits right into this category. To understand what a ketohexose is, let's break down the word: "keto" refers to a ketone group, and "hexose" signifies a six-carbon sugar. This means that ketohexoses are a type of carbohydrate that has a ketone group positioned along one of its carbon chains.

Fructose, being a ketohexose, boasts six carbon atoms in its structure. These are arranged in such a way that there is a ketone functional group, differentiating it from an aldose, which would have an aldehyde group instead.

Ketohexoses like fructose are unique because their structures allow them to be very sweet. This explains why fructose is commonly found in many fruits, adding that delightful sweetness. Understanding its ketohexose structure helps explain why fructose can be both a sugar source and an energy provider.

The Role of Optical Isomerism

Optical isomerism is a fascinating concept affecting sugars like fructose. It refers to the ability of a molecule to exist in two forms that are mirror images of each other, much like left and right hands.

This phenomenon occurs due to the presence of chiral centers, which are carbon atoms bonded to four different groups. Fructose exhibits optical isomerism, having more than one chiral center, and thus it can have multiple optical isomers. These isomers are known as enantiomers, with levorotatory (left-rotating) and dextrorotatory (right-rotating) forms.

For fructose, the naturally occurring form is levorotatory, leading to its alternate name, leavulose. Optical isomerism not only affects how molecules like fructose are named but also influences how they react in biological systems, impacting their sweetness and how they're metabolized by organisms.