Tag: Hydrogen Bonds

Introduction

The terms nucleophile and electrophile were coined by Christopher Kelk Ingold in 1933 to replace A. J. Lapworth’s anionic and cationic terminology. The term “electrophile” is a result of merging the words “electro,” denoting electrons, and “philes,” indicating a sentimental attachment. The word nucleophile comes from the combination of the Greek word ‘Philos,’ which means buddy, and the word nucleus. The field of chemistry relies heavily on these two concepts. Many organic reactions rely on the presence of these chemical substances. Electrophiles and nucleophiles, whose opposing behaviour is the impetus for many chemical processes, are well-known entities. Thus, it is clear that these definitions are crucial for a full comprehension of chemical processes.

Overview of Nucleophiles

Chemical species known as nucleophiles are able to give up a pair of electrons. They give up electrons because they are a species with an abundance of electrons. The word nucleophiles can be broken down into its component parts to denote any species that shows a preference for the nucleus. They are referred to be Lewis bases because of their ability to donate the pair of electrons they already possess. Lone-pair-of-electron species and negatively charged species are examples of neutral species. These chemical species are the ones that give up their pair of electrons during a chemical reaction, resulting in the creation of covalent bonds.

Nucleophilicity, which is comparable to the term basicity, describes the degree to which specific nucleophiles can transfer the pair of electrons. The element ammonia is a good example of a nucleophile because it has an unpaired electron.

Examples of Nucleophiles

As nucleophiles are negatively charged or they are species that contain lone pair of electrons. Some examples of nucleophiles can be given as, 

• All the halogen anions,\(B{r^ – },C{l^ – },{I^ – }\)
• Cyanide,\(C{N^ – }\)
• Ammonia, \({NH_3}\)
• Hydroxide ion

Structure of hydroxide ion

Features of Nucleophiles

This section elaborates on some of the key characteristics that nucleophiles must process.

1. There must be a net negative charge on a nucleophile, or it must have a lone pair of electrons if it is an electrically neutral species. Therefore, nucleophiles are typically anions.
2. A decreased electronegativity is required of nucleophiles in order for them to donate electron pairs effectively, so that they can be considered an inventive nucleophile. As a result, nucleophiles are often composed of less electronegative species.
3. The strength of nucleophiles can be affected by the solvent used in a chemical reaction, especially if the solvent is polar or protic and acts upon the nucleophiles.
4. Polar solvents can create hydrogen bonds with nucleophiles’ lone pairs of electrons, decreasing the likelihood that the nucleophiles will donate their electrons to other molecules.
5. The rate of nucleophilic reactions can be slowed if nucleophiles are sterically hindered. 

Overview of Electrophiles

Chemical substances having electron deficiency are called electrophiles. As a result, it attracts electrons towards itself since it has high electronic efficiency.

Two individual words, “electro” and “philes,” make up the phrase “electrophiles.” Electrophiles is a compound term that means “electron-loving species.” These substances might be either positively or neutrally charged chemical species. These compounds will take part in addition and substitution processes involving electrophiles. When they like interacting with a partner electron, electrophiles are referred to be Lewis acids. For this reason, the creation of a covalent bond is contingent upon the presence of these chemical species, which are able to accept a pair of electrons as part of a chemical reaction.

Examples of Electrophiles

Features of Electrophiles

We’ll go through what makes a good electrophile, and what makes a bad one, in more depth below.

1. In order to accept electrons from reacting nucleophiles, an electrophile must be positively charged or have an unoccupied orbital.
2. To attract electrons, an electrophile needs to have a weak link, hence electrophiles typically have weak polar bonds.
3. Because of steric hindrance, electrons cannot be transferred to electrophiles if they are too close to other electrophiles. Thus, an electrophile should not be sterically hindered. 

Difference Between Electrophiles and Nucleophiles

Some of the differences between electrophiles and nucleophiles are tabulated in the following table.

Summary

Chemical reactions take place by the donation and acceptance of electrons from one species to another species. Electrophiles and nucleophiles are two important chemical species that are necessary to undergo a chemical reaction. Electrophiles are the species that are positively charged or it a container back in the orbital to acceptive electrons. While nucleophiles are the chemical species that negatively charge lone pair of electrons so that they can donate this pair of electrons to another species. Some of the examples of electrophiles are \({BF_3}\) ,\({AlCl_3}\)

etc. And examples of nucleophiles are, \(C{N^ – },O{H^ – }\), etc. The important features of electrophiles and nucleophiles are affected by factors such as charge, electronegativity, steric hindrance, etc.

 

Frequently Asked Questions

1. Which of the following is the most powerful nucleophile in a nonpolar solution: I, Br, Cl, or F? 

Ans. Since the strength of a nucleophile increases with increasing electronegativity in nonpolar solutions, fluorine (F) is the most potent nucleophile in such a medium. As far as electronegativity goes, fluorine is the winner. That’s why it’s the strongest nucleophile there is.

2. What is the effect of solvent on nucleophilicity of a molecule?

Ans. Nucleophilic replacements benefit from more polar solvents since the nucleophile is generally an ionic molecule and needs to be dissolved in a polar solvent. Ions may be more stable in polar solvents than in others.

3. Why is \({BH_3}\) an electrophile?

Ans. \({BH_3}\) is an electrophile since the boron atom has an empty p orbital and an electron deficiency. Thus it easily acts as an electrophile. 

Introduction

Among the several intermolecular forces that exist, Van der Waals forces are notable. Johannes Diderik van der Waals, a Dutch scientist, proposed them in 1873 and so they bear his name. When compared to other intermolecular forces like hydrogen bonding and ionic bonding, Van der Waals forces are weak. Nonetheless, they continue to play a significant role in numerous branches of chemistry and physics.

In contrast to covalent and ionic bonding, which are both based on shared electrostatic repulsion between atoms, weak interactions are facilitated by correlations between the wildly varying polarisations of neighbouring particles (a consequence of quantum dynamics).

What are Van Der Waals forces?

Van Der Waals forces refer to the attractive and repulsive interactions that act between molecules and between atoms. The polarisation variations of neighbouring particles create these bonds, setting them apart from covalent and ionic interactions.

As a result of transient dipoles formed by the unequal distribution of electrons, molecules are attracted to one another via Van der Waals forces. This may occur due to the proximity of two molecules or the presence of a persistent dipole in one of the molecules. Because of the dipoles, the molecules are drawn to each other via a van der Waals force.

Characteristics 

• Covalent bonds involve electron sharing, while ionic bonds require one or both atoms to give up an electron. They’re both attracted to each other with a force that’s orders of magnitude stronger than Van Der Waals’.
• Multiple independent interactions compose them, making them cumulative.
• These forces do not have a direction and are thus impossible to fully exhaust.
• They do not vary with variations in temperature. This is because the amplitude of these forces is greatest when the interacting molecules or atoms are in close proximity to one another, and they only act across a short distance.

Types of Van Der Waals Forces

London Dispersion Forces

When the electrons in two neighbouring atoms are in locations that cause the atoms to form temporary dipoles, an attractive attraction known as the London dispersion force is produced. An induced dipole-induced dipole attraction is another name for this force.

Dipole-Dipole interaction

Two polar molecules attract one another due to the attraction forces of their constant dipoles. These dipoles are formed because of the disparities in electronegativity between neighbouring atoms.

Hydrogen Bonds

These are unique dipole-induced dipole interactions between hydrogen atoms and highly electronegative atoms such as oxygen, nitrogen and fluorine. 

Debye forces

These forces emerge when attractive Coulomb forces between permanent dipoles are outweighed by the strength of interactions between the permanent dipoles and other atoms/molecules.

Factors affecting Van Der Waals forces

Nature of element

The nature of an element or a non-metal is determined by the strength of its Van Der Waals forces. Elements or non-metals found in a liquid or gaseous state rely on these forces, whereas some metals use cohesive forces.

Electron count in an atom/molecule

In a periodic table, the atomic radius and the number of electrons held by each nucleus both grow as one descends from group to group There are more opportunities for transient dipoles to occur when the number of electrons is high. When there are many dipoles in a solution, the Van Der Waals force between them becomes greater.

Shape of molecule

The chemical structure of a molecule—whether it is branched or unbranched—can affect the strength of intermolecular forces, which in turn affects boiling points. 

Size of an atom

Attractive bonds have different strengths depending on the sizes of the atoms involved. The intermolecular interactions between atoms strengthen as the size of an atom grows.

Shape of an atom

The strength of an atom’s intermolecular forces depends on the shape of its molecules. Thin molecules have more potential to develop temporary dipoles than short, fat ones.

Applications of Van Der Waals forces

• Van Der Waals forces aid in protein folding and further solidify the protein in its final structure.
• They also facilitate the bonding of graphenes within graphite by acting as lubricants.
• Research and development in fields like supramolecular chemistry, nanotechnology, and polymer synthesis.
• For the most part, they are responsible for keeping the inert gases in a solid or liquid form.
• Due to the attracting force exerted at the ends of their feet, geckos can quickly and easily scale smooth surfaces.
• Spiders are similar in structure.

Summary

Molecules are attracted to one another by forces known as van der Waals forces. The two most common kinds of van der Waals forces are the weak London Dispersion Interactions and the larger dipole-dipole forces. They are influenced by many different things, such as the elements themselves, the molecular and atomic structures they are made of, and the sizes and shapes of their constituent parts.

Frequently asked questions

1. How do Van de Waal forces affect the viscosity of a substance?

Ans. Van de Waal forces can increase the viscosity of a substance by increasing the attraction between molecules, which makes it more difficult for them to move past each other.

2. Write the equation of Van Der Waals forces.

Ans. (P+n2a/V2) (V-nb) ＝ nRT

The above equation demonstrates the main two kinds of properties present – the volume of both elements and the attractive forces between them.

3. What is the use of the Van Der Waals equation?

Ans. The Van Der Waals equation is helpful in calculating an actual value in the case of non-ideal gases.