Electron-deficient atoms/molecules

In the Lewis acid-base definition, an acid is any species that accepts a lone pair to form a new bond in an adduct. Thus, there are many more Lewis acids than other types. Lewis adds include molecules with electron-deficient atoms, molecules with polar multiple bonds, and metal cations. 

Charge-Transfer Forces. An electron-rich atom, or orbital, can form a bond with an electron-deficient atom. Typical examples are lone pairs of electrons, eg, in nitrogen atoms regularly found in dyes and protein and polyamide fibers, or TT-orbitals as found in the complex planar dye molecules, forming a bond with an electron-deficient hydrogen or similar atom, eg, —0 . These forces play a significant role in dye attraction. 

Electrophiles, the most common type of reactive intermediate, are molecules with an electron-deficient atom, so having a full or partial positive charge. 

The oxyanion produced in the first step can help stabilize the electron-deficient BH3 molecule by adding to its empty p orbital. Now we have a tetravalent boron anion again, which could transfer a second hydrogen atom (with its pair of electrons) to another molecule of aldehyde. 

Nucleophile An ion or molecule that donates a pair of electrons to an electron-deficient atom so that a new covalent bond is formed. 

The octet rule is a useful guide for most molecules with Period 2 central atoms, but not for every one. Also, many molecules have central atoms from higher periods. As you ll see, some central atoms have fewer than eight electrons around them, and others have more. The most significant octet rule exceptions are for molecules containing electron-deficient atoms, odd-electron atoms, and especially atoms with expanded valence shells. 

The Lewis acid-base definition focuses on the donation or acceptance of an electron pair to form a new covalent bond in an adduct, the product of an acid-base reaction. Lewis bases donate the electron pair, and Lewis acids accept it. Thus, many species that do not contain El are Lewis acids. Molecules with polar double bonds act as Lewis acids, as do those with electron-deficient atoms. Metal ions act as Lewis acids when they dissolve in water, which acts as a Lewis base, to form an adduct, a hydrated cation. Many metal ions function as Lewis acids in biomolecules. 

Understanding bond polarity is critical to understanding how organic reactions occur, because a central rule that governs the reactivity of organic compounds is that electron-rich atoms or molecules are attracted to electron-deficient atoms or molecules. Electrostatic potential maps (often simply called potential maps) are models that show how charge is distributed in the molecule under the map. Therefore, these maps show the kind of electrostatic attraction an atom or molecule has for another atom or molecule, so you can use them to predict chemical reactions. The potential maps for LiH, H2, and HF are shown below. 

Electron-rich atoms or molecules are attracted to electron-deficient atoms or molecules. 

In essence, organic chemistry is about the interaction between electron-rich atoms or molecules and electron-deficient atoms or molecules. It is these forces of attraction that make chemical reactions happen. From this follows a very important rule that determines the reactivity of organic compounds Electron-rich atoms or molecules are attracted to electron-deficient atoms or molecules. Each time you study a new functional group, remember that the reactions it undergoes can be explained by this very simple rule. 

Therefore, to understand how a functional group reacts, you must first learn to recognize electron-deficient and electron-rich atoms and molecules. An electron-deficient atom or molecule is called an electrophile. An electrophile can have an atom that can accept a pair of electrons, or it can have an atom with an unpaired electron and, therefore, is in need of an electron to complete its octet. Thus, an electrophile looks for electrons. Literally, electrophile means electron loving (phile is the Greek suffix for loving ). 

All compounds with a particular functional group react similarly. Due to the cloud of electrons above and below its TT bond, an alkene is an electron-rich molecule, or nucleophile. Nucleophiles are attracted to electron-deficient atoms or molecules, called electrophiles. Alkenes undergo electrophilic addition reactions. The description of the step-by-step process by which reactants are changed into products is called the mechanism of the reaction. Curved arrows show which bonds are formed and which are broken and the direction of the electron flow that accompany these changes. 

Basicity is a measure of how well a compound shares its lone pair with a proton. Nucleophilicity is a measure of how readily a compound is able to attack an electron-deficient atom. In comparing molecules with the same attacking atom or with attacking atoms of the same size, the stronger base is a better nucleophile. If the attacking atoms are very different in size, the relationship between basicity and nucleophilicity depends on the solvent. In protic solvents, stronger bases are poorer nucleophiles because of ion-dipole interactions between the ion and the solvent. 

The component 6 of solubility parameter includes dispersive interactions energy and dipole bonds interaction energy and the component 6 - hydrogen bonding interaction and the interaction energy between an electron-rich atom of one molecule (donor) and an electron-deficient atom of another molecule (acceptor), which requires a certain orientation of these two molecules. In such treatment there is no need to introduce a separate component for interaction between polar molecules description. 

Electrophile An electron-deficient atom, ion, or molecule that has an affinity for an electron pair, and will bond to a base or nucleophile. In general, electrophiles (literally electron-lover) are positively charged or neutral species that participate in a chemical reaction by accepting an electron pair in order to bond to a nucleophile. Because electrophiles accept electrons, they are Lewis acids. 

Electron counting works for most atoms, yet special cases exist where atoms have less or more than the noble gas configuration you re aiming for. Atoms with less electrons, commonly seen with boron and aluminum, are known as electron-deficient. Atoms with more electrons, such as certain sulphur, phosphorus, silicon, iodine, and xenon molecules, aire known as hypervalent or... 

If the acid-base reaction is written with the electron pairs and the arrows, as shown for water and HCl, the Lewis base definition is quite useful. The electron-rich molecule is the base, and the electron-rich atom donates two electrons. The molecule bearing the electron-deficient atom (hydrogen) is the acid. For reactions of organic molecules, it is essential to identify electron-rich and electron-poor components of molecules, to understand the electron flow, and to understand how to predict the products. That process begins with making the transition to thinking in terms of Lewis bases/Lewis acids rather than Br0nsted-Lowry acids and bases. 

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