All structures given below are of vitamin $C$ Most stable of them is :
Show Hint
Resonance stabilization is a key factor in determining the stability of molecules. Look for structures with the greatest delocalization of electrons. For Ascorbic acid, the enediol system adjacent to the carbonyl group is responsible for stability.
The Correct Option is A
Solution and Explanation
Step 1: Analyze the Structures
All four structures represent ascorbic acid (vitamin C), but they differ in the position of the double bond within the ring and the configuration of the hydroxyl groups.
Step 2: Consider Resonance Stabilization
The most stable structure will be the one with the greatest resonance stabilization. Structure (1) has the most resonance structures possible because the double bond is conjugated with the carbonyl group, allowing for delocalization of electrons. This delocalization stabilizes the structure more than the other structures. Also, the hydroxyl group on C2 will donate electron density to the carbonyl group at C1, whereas in structure 2 the carbonyl group will pull electrons making it unstable.
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Concepts Used:
Hydrogen Bonding
Hydrogen bonding implies the formation of hydrogen bonds which are an attractive intermolecular force. An example of hydrogen bonding is the bond between the H atom and the O atom in water.
A special type of intermolecular attractive force arises only in the compounds having Hydrogen atoms bonded to an electronegative atom. This force is known as the Hydrogen bond. For instance, in water molecules, the hydrogen atom is bonded to a highly electronegative Oxygen.
The conditions for hydrogen bonding are:
- The molecule must contain a strongly electronegative atom that is bound to the hydrogen atom. The higher the electronegativity, the more polarized is the molecule.
- The electronegative atom must be small. The smaller the size, the greater the electrostatic magnetism.
Effects of Hydrogen Bonding on Elements:
Association: The molecules of carboxylic acids exist as dimer because of the hydrogen bonding. The molecular masses of such compounds are found to be double than those calculated from their simple formula.
Dissociation: In aqueous solution, HF dissociates and gives the difluoride ion instead of fluoride ion. This is due to hydrogen bonding in HF. The molecules of HCl, HBr, HI do not form a hydrogen bond. This explains the non-existence of compounds like KHCl2, KHBr2, KHI2.
Types of Hydrogen bonding
- Intramolecular Hydrogen bonding: When hydrogen bonding takes place between different molecules of the same or different compounds, it is called intermolecular hydrogen bonding.
- Intermolecular hydrogen bonding: The hydrogen bonding which takes place within a molecule itself is called intramolecular hydrogen bonding.
- Symmetrical Hydrogen bonding: The symmetric hydrogen bond is a type of a three-centre four-electron bond.