Question

In which of the following species, intramolecular Hbonding occurs? 1\. Acetate ion 2\. Salicylate ion 3\. Propanoic acid 4\. O-nitrophenol (a) \(1,3,4\) (b) \(1,2,4\) (c) 2,4 (d) 4 only

Short answer

(c) 2,4

Step-by-step solution

Identifying Intramolecular Hydrogen Bonding

Intramolecular hydrogen bonding occurs within a molecule, where a hydrogen atom is shared between two electronegative atoms. Common donors and acceptors for hydrogen bonding include: - Donor: OH, NH groups - Acceptor: Oxygen in carbonyls (C=O), Nitrogen or Halogens We need to identify any possibilities in the given species: acetate ion, salicylate ion, propanoic acid, and o-nitrophenol to check for these criteria.

Analysis of Each Species

1. **Acetate ion**: Lacks an optimal position for intramolecular hydrogen bonding because its oxygen atoms are involved in resonance stabilization rather than bonding with each other. 2. **Salicylate ion**: Contains a hydroxyl group (-OH) and an adjacent carboxylate group, allowing for interaction between them through hydrogen bonding. 3. **Propanoic acid**: Although it contains a hydrogen (H) and a C=O (carbonyl group), the spatial arrangement is not conducive to intramolecular hydrogen bonding. 4. **O-nitrophenol**: Has a hydroxyl group (OH) and a nitro group (NO2) ortho to each other, which can allow intramolecular hydrogen bonding between them.

Determine Which Options Meet Criteria

Based on the analysis, salicylate ion and o-nitrophenol exhibit intramolecular hydrogen bonding. The functional groups are positioned correctly for interaction in these compounds, fulfilling the condition for intramolecular hydrogen bonds.

Key concepts

Hydrogen Bonding

Hydrogen bonding is a special type of intermolecular force that occurs when a hydrogen atom is covalently bonded to a highly electronegative element, such as oxygen, nitrogen, or fluorine. This leads to the hydrogen atom carrying a partial positive charge. It can then interact electrostatically with another electronegative atom having a lone pair of electrons. Hydrogen bonds are fundamental in many chemical processes, having significant effects on the structure and properties of substances.

In the context of the exercise, intramolecular hydrogen bonding specifically refers to hydrogen bonds occurring within the same molecule rather than between different molecules. This can stabilize the structure of the molecule by creating a sort of "ring" through the hydrogen bond. The presence of specific functional groups in proximity, such as hydroxyl groups (-OH) and carbonyl groups (C=O), is key for intramolecular hydrogen bonds to form.

• Donor Groups: Typically contain hydrogen, like -OH (hydroxyl) or -NH (amino) groups.
• Acceptor Units: Often electronegative atoms such as oxygen found in C=O groups, nitrogen in amino groups, or halogens.

This interaction is an essential factor in molecular geometry and stability.

Organic Chemistry

Organic chemistry involves the study of carbon-containing compounds, which are central to biological processes and a vast number of synthetic materials. Carbon's ability to form four covalent bonds enables it to create complex structures with various shapes and functional groups. Functional groups are specific groups of atoms within molecules that determine the characteristic reactions of those molecules.

Understanding the presence and arrangement of these functional groups is critical for predicting the behavior and reactivity of organic molecules. In the exercise, the functional groups play a crucial role in identifying potential hydrogen bond donors and acceptors. For instance, molecules like o-nitrophenol and the salicylate ion have suitable functional group proximity for intramolecular hydrogen bonding.

• Electronegativity and Localization: Electrons tend to be drawn towards more electronegative atoms in a bond, leading to partial charges and potential hydrogen bonding.
• Functional Groups at Play: Hydroxyl (-OH), carboxylate (-COO⁻), and nitro (NO₂) groups influence hydrogen bonding potential.

These principles help understand reaction mechanisms and molecular interactions in organic compounds.

Molecular Geometry

Molecular geometry is the three-dimensional arrangement of atoms in a molecule. This structure determines numerous physical properties and chemical behavior, including the ability to form hydrogen bonds. Geometry affects how close functional groups are to each other, which is crucial for the potential for intramolecular hydrogen bonding. For example, if functional groups are too far apart, even if they are suitable as donors and acceptors, hydrogen bonding may not occur.

The spatial arrangement and resultant molecular geometry can influence a molecule's chemical reactivity and interaction capabilities. In the exercise, molecules like o-nitrophenol and the salicylate ion exhibit a configuration where functional groups are ideally positioned for intramolecular hydrogen bonding.

• Ortho Positioning: Functional groups on adjacent carbons in a benzene ring can lead to effective hydrogen bonding.
• Influence of Bond Angles: The angle between bonds can influence the proximity of groups required for hydrogen bonding.

These spatial considerations are essential when analyzing and predicting the chemical behavior of a molecule in the context of its environment.