Name: alkene addition reactions and redox changes
Uploaded: 2023-04-30T18:28:36.000Z
Duration: 2 min 24 s
Channel: JoVE
Description: Alkene addition reactions show how a carbon-carbon double bond reacts with electrophiles and changes during the process. A simple, unconjugated alkene has a double bond with high electron density, so it can act as a weak base or a nucleophile. Its filled π orbital, called the HOMO, can interact with the empty LUMO of an electrophile.

Simple, unconjugated alkenes are electron-rich and can function as weak bases or nucleophiles. The filled &#960; orbital of the double bond, which is the HOMO, can interact with the LUMO of an electrophile, such as bromine.
An addition reaction begins with the transfer of a pair of electrons from the &#960; bond to the electrophilic center. A &#963; bond is formed between the electrophile and one of the carbons, while the other carbon acquires a positive charge. The carbocation then reacts with a nucleophile to form a &#963; bond, yielding the addition product.
An addition reaction and the corresponding elimination reaction can be represented as a temperature-dependent equilibrium.
In an addition reaction, one &#960; and one &#963; bond are broken and two &#963; bonds are formed. Because &#963; bonds are stronger than &#960; bonds, addition reactions are usually exothermic.
Thus, in the equation for Gibbs free energy change, the enthalpy term is negative. The decrease in the number of molecules indicates that the entropy term is always positive.
Consequently, for low values of T, the value of &#916;G is negative, and addition reactions are thermodynamically favored at low temperatures.
In the halogenation of alkenes, bonds are for

introduction to electrophilic addition reactions of alkenes

Introduction to Electrophilic Addition Reactions of Alkenes

The double bond in a simple, unconjugated alkene is a region of high electron density that can act as a weak base or a nucleophile. The filled &#960; orbital (HOMO) of the double bond can interact with the empty LUMO of an electrophile. A bonding interaction occurs when the electrophile attacks between the two carbons; the electrophile then accepts a pair of electrons from the &#960; bond and undergoes addition across the double bond, yielding a single product.
Addition and elimination reactions can be considered to exist in a temperature-dependent equilibrium, which can be better understood from the change in Gibbs free energy (&#916;G) of the reaction. In addition reactions, one &#960; bond is broken, and two &#963; bonds are formed. These reactions are usually exothermic because &#963; bonds are stronger than &#960; bonds; thus, the enthalpy term (&#916;H) is negative. The entropy term (&#8722;T&#916;S) is always positive: the number of molecules decreases, leading to a negative &#916;S, and T is always positive on the kelvin scale, so the negative of that product is a positive term overall. Consequently, the value of &#916;G is dependent on the temperature of the system, and addition reactions are favored at low temperatures.
When an alkene undergoes halogenation, bonds are formed between carbon and the more electronegative halogens; thus, the carbon atoms are oxidized. Dihydroxylation, halohydrin formation, and epoxidation are also oxidation reactions. Conversely, the addition of hydrogen across the double bond in alkenes is a reduction reaction that yields the corresponding alkanes. In hydration and hydrohalogenation reactions, one of the carbon atoms is oxidized while the other is reduced; as a result, they are not classified as oxidation or reduction reactions. In the hydrobromination of but-2-ene, the acidic proton in HBr accepts a pair of electrons from the &#960; bond. The proton is transferred to one of the carbons in the double bond, while the other carbon acquires a positive charge, resulting in a secondary carbocation intermediate. The bromide ion then reacts with the positive center to yield a racemic mixture of 2-bromobutane.

The double bond in a simple, unconjugated alkene is a region of high electron density that can act as a weak base or a nucleophile. The filled &#960; ...

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Organic Chemistry

Unit 1

Alkene Structure and Reactivity

KEY TERMS AND CONCEPTS

alkene addition reactions and redox changes

Alkene addition reactions show how a carbon-carbon double bond reacts with electrophiles and changes during the process. A simple, unconjugated alkene has a double bond with high electron density, so it can act as a weak base or a nucleophile. Its filled π orbital, called the HOMO, can interact with the empty LUMO of an electrophile.

Alkene Addition Reactions and Redox Changes

alkene-addition-reactions-and-redox-changes

regioselectivity of electrophilic additions to alkenes: markovnikov's rule

regioselectivity-electrophilic-additions-to-alkenes-markovnikov-s

Markovnikov Addition Paths in Alkenes

Markovnikov addition in alkenes explains why one product often forms in greater amount during hydrohalogenation. When an unsymmetrical alkene reacts, two haloalkane constitutional isomers are possible. In most cases, hydrogen adds to the vinylic carbon with more hydrogens, and the halide part adds to the more substituted carbon. This preference is called regioselectivity. Regioselective reactions favor bond formation at one site over another, so one constitutional isomer becomes the major...

structure and bonding of alkenes

Alkene Bonding, Properties, and Uses

Alkenes are unsaturated hydrocarbons with one or more carbon-carbon double bonds. They are also called olefins, and they are broadly divided into alkenes and cycloalkenes. The general formula for an alkene is CnH2n. The carbons in a double bond are sp2 hybridized. This gives each carbon a trigonal planar shape. The double bond has two parts: a sigma bond from overlap of hybrid orbitals and a pi bond from side-by-side overlap of unhybridized 2p orbitals. Each carbon also bonds to two hydrogen...

nomenclature of alkenes

IUPAC Rules for Alkene Naming

IUPAC rules for alkene naming show how to name carbon chains with a double bond. A simple alkene changes the alkane suffix -ane to -ene. The double bond must be part of the parent chain, which is the longest carbon chain that contains the maximum number of double bonds. The chain is numbered so the doubly bonded carbon atoms get the lowest possible numbers. The location of the double bond is given by the number of its first carbon atom. In branched alkenes, the double bond takes priority over...

degree of unsaturation

Counting Rings and Double Bonds in Molecules

Degree of unsaturation helps count rings and double bonds in an organic molecule. It is also called the index of hydrogen deficiency, or IHD. The idea is based on comparing a compound with the acyclic alkane that has the same number of carbon atoms. Each double bond or ring removes two hydrogen atoms compared with a saturated analog. That loss equals one degree of unsaturation. For hydrocarbons, the formula is U = (2C + 2 - H) / 2, where C is the number of carbon atoms and H is the number of...

isomerism in alkenes

Cis, Trans, and E/Z Alkene Forms

Alkene isomers can differ in both bond position and spatial arrangement. 1-butene and 2-butene are constitutional isomers because the double bond is in a different place. 2-butene also shows stereoisomerism, which means its atoms are connected the same way but arranged differently in space. In 2-butene, the two methyl groups can sit on the same side of the double bond or on opposite sides. When the methyl groups are on the same side, the compound is called cis-2-butene. When they are on...

relative stabilities of alkenes

Alkene Stability: Heat and Structure

Alkene stability depends on heats of hydrogenation and on the structure around the double bond. A lower heat of hydrogenation means the alkene is more stable. Three main factors help explain these differences: the number of substituents on the double-bond carbons, hyperconjugation, and double-bond stereochemistry. Substitution across the double bond has a strong effect on stability. An alkene with two smaller substituents is more stable than its isomer with one large substituent. For example,...

Alkene addition reactions show how a carbon-carbon double bond reacts with electrophiles and changes during the process. A simple, unconjugated alkene has a double bond with high electron density, so it can act as a weak base or a nucleophile. Its filled π orbital, called the HOMO, can interact with the empty LUMO of an electrophile.

key terms and concepts

Learn how alkene double bonds react with electrophiles, why addition is favored at low temperatures, and how these reactions connect to oxidation and reduction.

Alkene Addition Reactions and Redox Changes | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Alkene Addition Reactions and Redox Changes

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