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Chapter 7: Problem 152

How many optically active products are obtained on heating lactic acid?

Short Answer

Expert verified
On heating lactic acid, it undergoes a dehydration reaction, forming pyruvic acid as the product. Analyzing the structure of pyruvic acid reveals that there is no chiral center within the molecule. As a result, pyruvic acid is optically inactive. Hence, the number of optically active products obtained on heating lactic acid is 0.

Step by step solution

01

Draw the structures of L- and D-lactic acid

Draw the structural, Fischer projection, of both L- and D-lactic acid, with the chiral center represented by an asterisk: L-(+)-lactic acid: HO-CH\(_3\) *C(OH)-C(O)OH D-(-)-lactic acid: HO-C(O)OH*C(OH)-CH\(_3\)
02

Write the reaction for heating lactic acid

When lactic acid is heated, it undergoes a dehydration reaction, losing a water molecule. C3H6O3 (lactic acid) 鈫� C3H4O2 (pyruvic acid) + H2O
03

Draw the structure of the product, pyruvic acid

The product of the reaction is pyruvic acid, with the chemical formula C3H4O2. Draw the structure of pyruvic acid: Pyruvic acid: CH3-C(O)C(O)OH
04

Analyze the product for optical activity

Look at the product's structure to determine if there is any chiral center (a carbon atom with four different groups/bindings) within the molecule. Observe that pyruvic acid has no chiral center: CH3-C(O)C(O)OH Since there is no chiral center in the product, it is not optically active.
05

Summarize the result

On heating lactic acid, we obtain pyruvic acid as the product. Pyruvic acid lacks any chiral center, making it an optically inactive compound. Therefore, the number of optically active products obtained on heating lactic acid is 0.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lactic Acid
Lactic acid is an organic compound, commonly known in the world of biochemistry and medicine for its role in various metabolic processes. It is a simple carboxylic acid with the chemical formula C\(_3\)H\(_6\)O\(_3\). Lactic acid exists in two optical isomers, L-(+)-lactic acid and D-(-)-lactic acid, due to its chiral center.

Let's break down what makes this compound unique:
  • Lactic acid contains one hydroxyl group (-OH) and a carboxylic acid group (-COOH), which are attached to the central carbon atom.
  • It is commonly found in sour milk products, and it's also produced in muscle tissues during strenuous activity, leading to temporary muscle fatigue.
  • The presence of a chiral center in lactic acid means that it can rotate plane-polarized light, contributing to its optical activity.
Understanding lactic acid is vital in various fields of science and industry, from food preservation to exercise physiology.
Chiral Center
In chemistry, a chiral center is a fascinating aspect of molecular structure that explains a lot about molecular behavior. A chiral center, often marked with an asterisk (*), refers to a carbon atom bonded to four different groups. This unique feature gives rise to molecules that have non-superimposable mirror images, also known as enantiomers.

Here's what to know about chiral centers:
  • A molecule with at least one chiral center can exhibit optical activity, meaning it can rotate plane-polarized light.
  • The presence of a chiral center in lactic acid is what allows it to exist as two enantiomers, L- and D-lactic acid. Each isomer has distinct physiological effects.
  • To identify a chiral center, look for a tetrahedral carbon with four different substituents.
In lactic acid, the chiral center is the key to its optical properties. When lactic acid is transformed into pyruvic acid by heat, the chiral center is lost, affecting its optical activity.
Pyruvic Acid
Pyruvic acid is a crucial molecule in biochemistry, primarily known as the end product of glycolysis and a starting point for various metabolic pathways. With the chemical formula C\(_3\)H\(_4\)O\(_2\), it's a simple alpha-keto acid that arises when lactic acid is heated and dehydrated. Notably, pyruvic acid lacks a chiral center.

Important points about pyruvic acid include:
  • Pyruvic acid does not possess any chiral center, thus it is not optically active.
  • It serves as a pivotal intermediate in several biochemical processes, including fermentation and the citric acid cycle.
  • The conversion of lactic acid to pyruvic acid involves a dehydration reaction, which removes an element of optical activity since the resulting structure lacks the chiral characteristics.
Understanding pyruvic acid deepens one鈥檚 knowledge of how complex biological systems efficiently convert energy and manage metabolic waste.

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Most popular questions from this chapter

Choose the incorrect option(s): (A) (P) is known as Grignard reagent (B) Formation of \((Q)\) is nucleophilic addition reaction (C) Formation of (Q) involves carbanion as intermediate (D) Formation of \((\mathrm{R})\) involves acid base interaction

Total number of reactions in which carboxylic acid is obtained as a product is (a) \(\mathrm{R}-\mathrm{Cl} \frac{\text { (i) } \mathrm{Mg}}{\text { (ii) } \mathrm{CO}_{2}}\) (b) \(\mathrm{R}-\mathrm{Cl} \frac{\text { (i) } \mathrm{KCN}}{\text { (ii) } \mathrm{H}_{3} \mathrm{O}^{+}}\) (c) \(\mathrm{R}-\mathrm{CHO} \frac{\mathrm{CrO}_{3}}{\mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow}\) (d) \(\mathrm{R}-\mathrm{C}-\mathrm{Cl} \stackrel{\mathrm{H}_{3} \mathrm{O}^{+}}{\longrightarrow}\) (e) \(\mathrm{R}-\mathrm{CH}_{2} \mathrm{OH} \frac{\mathrm{CrO}_{3}}{\mathrm{H}_{2} \mathrm{SO}_{4}}\) (f) \(\mathrm{R}-\mathrm{CHO} \stackrel{\mathrm{Ag}_{2} \mathrm{O}}{\longrightarrow}\) (g) \(\mathrm{R}-\mathrm{NC} \stackrel{\mathrm{H}_{3} \mathrm{O}^{+}}{\longrightarrow}\)

For which value of \(n\) compound, \(\mathrm{HO}_{2} \mathrm{C}-\left(\mathrm{CH}_{2}\right)_{\mathrm{n}}-\mathrm{CO}_{2} \mathrm{H}\) undergo only dehydration on heating? (A) \(n=1\) (B) \(n=2\) (C) \(n=3\) (D) \(n=4\)

All acid derivatives on hydrolysis certainly give (A) Carboxylic acid (B) Alcohol (C) Aldehyde (D) Carbon dioxide

Ester can be reduced by: (A) DIBAL-H (B) \(\mathrm{Na}-\mathrm{C}_{2} \mathrm{H}_{2} \mathrm{OH}\) (C) \(\mathrm{NaBH}_{4}\) (D) \(\mathrm{CH}_{3} \mathrm{MgX}\)
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